Electrochemical cell in a sachet

Abstract

An electrochemical cell comprising: - an envelope having a first and a second compartment forming a main compartment when the outer envelope is folded around a folding axis, the first compartment being bounded transversely by a first edge and a second edge and parallel to the folding axis by a third edge; the second compartment being bounded transversely by a fourth edge and a fifth edge and parallel to the folding axis by a sixth edge; - the first and fourth edges being joined by a first heat-sealed junction, - the second and fifth edges being joined by a second heat-sealed junction, - the third and sixth edges being joined by a third heat-sealed junction; at least one of the junctions comprising a first portion of a first thickness and a second portion of a second thickness greater than the first thickness. Figure for the abbreviation: Fig. 2

Description

Title of the invention: Electrochemical cell in a sachet

[0001] The present invention relates to pouch electrochemical cells, also called pouch cells, flexible envelope cells or "Pouch cells" according to Anglo-Saxon terminology.

[0002] In a manner known from the prior art, a Pouch type electrochemical cell comprises an outer envelope or pouch containing an alternating stack of negative and positive electrodes separated from each other by a porous separator film soaked in electrolyte.

[0003] The envelope is most often formed by heat sealing (also called heat bonding) the edges of two multilayer films or strips, each having a thermoplastic layer on its facing inner surfaces. The envelope is hermetically sealed by placing its edges between two heated jaws that melt the surface polymers, thus sealing the cell in a pouch so that only a positive terminal and a negative terminal, connected to the corresponding electrodes, remain exposed.

[0004] In order to reduce the edges to be heat-sealed and, consequently, improve the sealing of the casing, it is also known that the casing may be pre-formed in the form of a double sheet incorporating two identical recesses (or cavities) on either side of a fold line. When folded over each other, the two recesses together form a casing intended to receive the stack of electrodes and the electrolyte.

[0005] The bagged electrochemical cells thus obtained are juxtaposed next to each other in an electric battery module.

[0006] Although these bagged cells offer advantages in terms of flexibility and energy density, their sensitivity to high internal or external pressure is a major drawback, requiring additional precautions in design and assembly to contain any excessive pressure to which a bagged cell of the battery module might be subjected.

[0007] Overpressure can indeed occur due to gases generated during the charging / discharging cycles of a bagged cell or due to excessive or uneven compression and / or deformation of the cell. Overpressure most often leads to thermal runaway, compromising the structural integrity of the bagged cell.

[0008] This thermal runaway phenomenon causes the rupture of the bag cell's outer casing and an uncontrolled release of flammable gases at high temperatures (typically several hundred degrees Celsius). Very serious consequences (such as smoke, flames, or even an explosion of the cells) can therefore result, particularly for parts located near the bagged cells and / or for the passengers of the electric vehicle.

[0009] In this regard, additional structural supports such as rigid frames or compartments are often incorporated into battery modules. However, these measures remain ineffective as long as the current design of bagged cells does not allow for control of ruptures caused by thermal runaway.

[0010] An object of the present invention is to offer cells in sachets allowing better control of their rupture, if it occurs.

[0011] Another object of the present invention is to improve the safety of an electric battery module in the event of thermal runaway.

[0012] For this purpose, an electrochemical cell in a bag is proposed comprising: - a flexible outer casing having a first housing and a second housing, the first and second housing forming a main housing when the outer casing is folded around a folding axis, - at least one negative electrode and one positive electrode separated by an insulating separator and an electrolyte arranged in the main housing; cell in which the first housing is bordered transversely to the folding axis, along a transverse axis, by a first edge and by a second edge opposite to the first edge and parallel to the folding axis by a third edge; cell in which the second housing is bordered transversely to the folding axis, along the transverse axis, by a fourth edge and by a fifth edge opposite to the fourth edge and parallel to the folding axis by a sixth edge; cell in which: - the first edge and the fourth edge are joined together by a first heat-sealed junction, - the second edge and the fifth edge are joined together by a second heat-sealed junction, the third edge and the sixth edge are joined together by a third heat-sealed junction, the first, second and third heat-sealed junctions being intended to hermetically seal the main housing; cell in which at least one of the first, second and third heat-sealed junctions comprises a first heat-sealed junction portion and a second heat-sealed junction portion; - the first portion being of a predetermined first thickness, the second portion being of a second predetermined thickness greater than the first thickness, the first and second thicknesses being measured along a stacking axis perpendicular to the folding axis and the transverse axis; and / or - the first portion being of a first predetermined width, the second portion being of a second predetermined width less than the first width, the first and second widths being measured along an axis perpendicular to the stacking axis and to said at least one of the junctions; and / or - the first portion of heat-sealed joint comprising a predefined number of air bubbles per unit area and the second portion of heat-sealed joint comprising a second predefined number of air bubbles per unit area greater than said first number.

[0013] Various additional features may be provided, alone or in combination: - the second thickness is between 1.1 and 1.5 times the first thickness; - the first width is between 1.1 and 1.5 times the second width; - the first heat-sealed joint portion comprises a first number of sealing lines forming a multi-line sealing strip, the second heat-sealed joint portion comprising a second number of sealing lines less than said first number; - the first portion and the second portion belong to the third heat-sealed junction; - the second portion belongs to the first heat-sealed junction and to the third heat-sealed junction; - the second portion has a second length between 0.1 and 0.5 times a first length of the first portion, the first and second lengths being measured along said at least one of the junctions.

[0014] Other features and advantages of the invention will become clearer and more concrete upon reading the following description of embodiments, which is made with reference to the accompanying drawings in which:

[0015] Figure [Fig.1] schematically illustrates a pre-formed multilayer film in the form of a flexible outer casing for an electrochemical cell;

[0016] Figure [Fig.2] schematically illustrates the flexible outer casing of an electrochemical cell; the detail inset shows at an enlarged scale a heat-sealed edge of this casing according to various embodiments.

[0017] With reference to the accompanying figures, an electrochemical cell 10 in a bag is shown, comprising a flexible outer casing 20. This outer casing 20 has a first housing 21 (or cavity) and a second housing 22 which together form a main housing 23 when the outer casing 20 is folded (as indicated by arrow 14) around a folding axis 7.

[0018] Indeed, the first housing 21 and the second housing 22 have a common edge incorporating the folding axis 7 allowing the first housing 21 to fold down onto the The second housing 22 is thus formed to create the main housing 23, which is designed to receive a stack of electrodes and an electrolyte. In other words, the first housing 21 and the second housing 22 are contiguous along a common edge, incorporating the folding axis 7 that allows the housings 21 and 22 to be folded onto each other. When folded onto each other along the folding axis 7, the two housings 21 and 22 together define or form the main housing 23 for holding a stack of electrodes and an electrolyte.

[0019] The first housing 21 and the second housing 22 are substantially symmetrical with respect to the folding axis 7. The edges of the two housings 21, 22 align perfectly when these two housings 21, 22 are folded one onto the other. These edges refer to the outer limits of dwellings 21, 22 or to the peripheral area immediately around the two dwellings 21, 22. The substantially rectangular profile of dwellings 21, 22 is only for illustrative purposes and is in no way limiting.

[0020] The first housing 21 is bordered transversely to the folding axis 7, along the transverse axis 8, by a first edge 1 and by a second edge 2 opposite to the first edge 1 and parallel to the folding axis 7 by a third edge 3.

[0021] The second housing 22 is bordered transversely to the folding axis 7, along the transverse axis 8, by a fourth edge 4 and by a fifth edge 5 opposite to the fourth edge 4 and parallel to the folding axis 7 by a sixth edge 6.

[0022] A stack of electrodes and an electrolyte (not shown) are arranged in the main housing 23. More generally, the outer casing 20 incorporates at least one negative electrode and one positive electrode separated by an insulating separator and an electrolyte.

[0023] In one embodiment, the flexible envelope 20 is formed of a multilayer film comprising, from the outside to the inside of this flexible envelope 20, an electrically insulating protective outer layer (for example, made of plastic), an intermediate metallic layer (in particular, made of aluminum or an aluminum-based alloy) and an inner layer made of thermoplastic material (for example, made of polypropylene).

[0024] The electrochemical cell 10 in a sachet is closed by heat sealing so that only two electrical terminations (not shown) protrude from the flexible envelope 20, connected to the electrodes of opposite polarities of the stack to form the terminals of the electrochemical cell 10 in a sachet.

[0025] The first edge 1 and the fourth edge 4 are joined by a first heat-sealed joint 11. The second edge 2 and the fifth edge 5 are joined by a second heat-sealed joint 12. The third edge 3 and the sixth edge 6 are joined together by a third heat-sealed junction 13. These heat-sealed junctions 11, 12, 13 hermetically seal the main housing 23.

[0026] At least one of the heat-sealed junctions 11, 12, 13 comprises a first heat-sealed junction portion 31 having a first sealing impression and a second heat-sealed junction portion 32 having a second sealing impression different from the first sealing impression. In other words, at least one of the heat-sealed junctions 11, 12, 13 is non-uniform or irregular.

[0027] In one embodiment, the first portion 31 has a first predetermined thickness and the second portion 32 has a second predetermined thickness greater than the first thickness. The first and second thicknesses are measured along a stacking axis 9 perpendicular to the folding axis 7 and to the transverse axis 8, as illustrated by dimension 33 in [Fig.2].

[0028] This difference in thickness is manifested, in particular, in terms of resistance to a force tending to break the heat-sealed joint 11, 12, 13. In this case, the second portion 32 of the heat-sealed joint is less resistant than the first portion 31 to a pressure tending to break this joint.

[0029] Advantageously, this difference in thickness between the first portion 31 and the second portion 32 creates a weak point where the heat-sealed junction 11,12,13 can break in the event of a thermal runaway of the electrochemical cell 10 so as to be able to control / direct the release of gases and avoid the risks of an uncontrolled rupture.

[0030] In one embodiment, the second layer is between 1.1 and 1.5 times the thickness of the first layer. Such a ratio ensures airtight insulation of the main housing 23 and guarantees that the second portion 32 will rupture first in the event of thermal runaway of the electrochemical cell 10.

[0031] In another embodiment, the first portion 31 has a first predetermined width and the second portion 32 has a second predetermined width less than the first width. The first and second widths are measured along an axis perpendicular to the stacking axis 9 and to the heat-sealed junction 11, 12, 13 comprising the first and second portions 31, 32, as illustrated by dimension 34 in [Fig. 2].

[0032] In another embodiment, the first portion 31 of heat-sealed joint comprises a first number of sealing lines (for example, two or three lines) forming a multi-line sealing strip, while the second portion 32 of heat-sealed joint comprises a second number of sealing lines less than the first number (respectively, one or two lines).

[0033] Being less wide than the first portion 31, the second portion 32 has lower mechanical resistance, making it more susceptible to breaking. before the first section 31 in the event of thermal runaway of the electrochemical cell 10. The first width is, in one embodiment, between 1.1 and 1.5 times the second width. Such a ratio ensures airtight insulation of the main housing 23 and guarantees that the second section 32 will rupture first in the event of thermal runaway of the electrochemical cell 10.

[0034] In another embodiment, the first portion 31 of the heat-sealed junction comprises a predetermined number of air bubbles per unit area. In contrast, the second portion 32 of the heat-sealed junction comprises a higher concentration, with a predetermined number of air bubbles per unit area greater than that of the first portion 31.

[0035] This difference in concentration of air bubbles gives the second portion 32 less resistance to internal or external pressure exerted on the electrochemical cell 10 in the bag.

[0036] More generally, the second portion 32 is a specific section of the edge of the outer casing 20 where the heat-sealed joint is deliberately designed to be less resistant than on the rest of the edge. This target section allows for controlled failure in the event of excessive pressure on the flexible outer casing 20, ensuring that the rupture occurs at a predetermined location. This results in a controlled rupture of the outer casing 20, preventing more critical unforeseen damage.

[0037] A non-uniform (or irregular) heat-sealed junction 11, 12, 13 at the level of the second portion 32 (for example, having a greater thickness, a lesser width, or incorporating air bubbles) can be obtained using a sealing tool with a profiled heated jaw, allowing a different pressure to be applied to the first portion 31 and the second portion 32.

[0038] In one embodiment, the first portion 31 and the second portion 32 belong to the third heat-sealed junction 13. Such an arrangement of the second portion 32 allows, in the event of thermal runaway of the electrochemical cell 10, the gas release to be directed in a predefined direction opposite to the folding axis 7.

[0039] In another embodiment, the second portion 32 belongs to the first heat-sealed junction 11 and the third heat-sealed junction 13. In other words, the second portion 32 is at least partially contained within a corner of the flexible outer casing 20. Indeed, when pressure, particularly internal pressure, is applied to the electrochemical cell 10, the resulting forces are not distributed uniformly and are often greater at the corners. The at least partial presence of the second portion 32 within a corner promotes its initial rupture in the event of thermal runaway of the electrochemical cell 10.

[0040] More generally, the second portion 32 has a concave shape oriented towards the inside of the outer casing 20. This configuration is particularly advantageous because it acts as a point of convergence or a guide for internal pressure within the outer casing 20. By concentrating the forces at this second portion 32, its concave shape facilitates the rupture of the heat-sealed joint at this specific location, thus providing a controlled rupture mechanism in the event of thermal runaway of the electrochemical cell 10.

[0041] To ensure rapid escape of gases from the electrochemical cell 10 in the event of thermal runaway, while minimizing risks to surrounding elements near this electrochemical cell 10, it is preferable that the length of the second portion 32 be between 0.1 and 0.5 times the length of the first portion 31. This proportion allows the gases to be efficiently directed towards the intended rupture zone, thus ensuring controlled and safe depressurization. The lengths of the first and second portions 31, 32 are measured along the heat-sealed junction 11, 12, 13 integrating these two portions 31, 32, as illustrated by dimension 35 in [Fig. 2].

Claims

1. Demands Electrochemical cell (10) in a sachet comprising: - a flexible outer casing (20) comprising a first housing (21) and a second housing (22), the first and second housings (21, 22) forming a main housing (23) when the outer casing (20) is folded around a folding axis (7), - at least one negative electrode and one positive electrode separated by an insulating separator and an electrolyte arranged in the main housing (23); cell (10) in which, the first housing (21) is bordered transversely to the folding axis (7), along a transverse axis (8), by a first edge (1) and by a second edge (2) opposite to the first edge (1) and parallel to the folding axis (7) by a third edge (3); cell (10) in which, the second housing (22) is bordered transversely to the folding axis (7), along the transverse axis (8), by a fourth edge (4) and by a fifth edge (5) opposite to the fourth edge (4) and parallel to the folding axis (7) by a sixth edge (6); cell (10) in which: - the first edge (1) and the fourth edge (4) are joined together by a first heat-sealed junction (11), - the second edge (2) and the fifth edge (5) are joined together by a second heat-sealed junction (12), - the third edge (3) and the sixth edge (6) are joined together by means of a third heat-sealed junction (13), the first, second and third heat-sealed junctions (11,12,13) ​​being intended to hermetically seal the main housing (23); cell (10) in which at least one of the first, second and third heat-sealed junctions (11,12,13) ​​comprises a first heat-sealed junction portion (31) and a second heat-sealed junction portion (32); the first portion (31) being of a first predetermined thickness, the second portion (32) being of a second predetermined thickness greater than the first thickness, the first and second thicknesses being measured along an axis (9 ) stacking perpendicular to the folding axis (7) and the transverse axis (8); and / or the first portion (31) being of a first predetermined width, the second portion (32) being of a second predetermined width less than the first width, the first and second widths being measured along an axis perpendicular to the stacking axis (9) and to said at least one of the heat-sealed junctions (11,12,13); and / or the first portion (31) of heat-sealed junction comprising a predetermined number of air bubbles per unit area and the second portion (32) of heat-sealed junction comprising a second predetermined number of air bubbles per unit area greater than said first number.

2. Electrochemical cell (10) in a sachet according to the preceding claim, characterized in that the second thickness is between 1.1 and 1.5 times the first thickness.

3. Bag electrochemical cell (10) according to claim 1 or 2, characterized in that the first width is between 1.1 and 1.5 times the second width.

4. Electrochemical cell (10) in a bag according to any one of the preceding claims, characterized in that the first portion (31) of heat-sealed junction comprises a first number of sealing lines forming a multi-line sealing band, the second portion (32) of heat-sealed junction comprising a second number of sealing lines less than said first number.

5. Electrochemical cell (10) in a sachet according to any one of the preceding claims, characterized in that the first portion (31) and the second portion (32) belong to the third heat-sealed junction (13).

6. Bag electrochemical cell (10) according to any one of the preceding claims, characterized in that the second portion (32) belongs to the first heat-sealed junction (11) and to the third heat-sealed junction (13).

7. A sachet electrochemical cell (10) according to any one of the preceding claims, characterized in that the second portion (32) has a second length between 0.1 and 0.5 times a first length of the first portion (31), the first and the second length being measured along said at least one of the junctions (11,12,13).

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