FR3057708A1 - PROCESS FOR MANUFACTURING A LITHIUM BAG BATTERY, AND ASSEMBLY COMPRISING A CLOSED BAG COMPRISING ELECTRODES, FOR FILLING WITH A LIQUID ELECTROLYTE - Google Patents

Abstract

The invention relates to a method for filling a liquid electrolyte in a bag (3) intended to form the outer casing of a lithium battery in a bag, the method comprising introducing the electrolyte in a set (20) comprising the closed bag (3) containing electrodes, the introduction being carried out via a cannula (30) sealingly traversing a functional edge (26) of the bag (3) formed by two end of bag (3 ') superimposed and heat-welded, the cannula (30) being interposed between the two bag ends (3') and heat-welded thereto. The invention also relates to such a set (20), as well as to a manufacturing method implementing this set.

Description

Holder (s): COMMISSIONER OF ATOMIC ENERGY AND ALTERNATIVE ENERGIES Public establishment.

Extension request (s)

Agent (s): BREVALEX Limited liability company.

METHOD FOR MANUFACTURING A SACHET LITHIUM BATTERY, AND ASSEMBLY COMPRISING A CLOSED SACHET CONTAINING ELECTRODES, INTENDED TO BE FILLED WITH A LIQUID ELECTROLYTE.

FR 3 057 708 - A1

The invention relates to a method for filling a liquid electrolyte in a sachet (3) intended to form the outer envelope of a lithium battery in a sachet, the method comprising introducing the electrolyte into an assembly (20) comprising the closed bag (3) containing electrodes, the introduction being carried out by means of a cannula (30) sealingly crossing a functional edge (26) of the bag (3) formed by two ends of bag (3 ') superimposed and heat-sealed, the cannula (30) being interposed between the two ends of bag (3') and heat-welded thereto.

The invention also relates to such an assembly (20), as well as to a manufacturing process using this assembly.

PROCESS FOR MANUFACTURING A LITHIUM BATTERY IN A BAG,

AND ASSEMBLY COMPRISING A CLOSED BAG CONTAINING ELECTRODES, FOR FILLING WITH A LIQUID ELECTROLYTE

DESCRIPTION

TECHNICAL AREA

The present invention relates to the field of manufacturing a lithium battery in a sachet, also known as a flexible sachet battery or a battery in a flexible envelope, or also a “Pouch Cell” battery.

It relates to lithium batteries in sachets comprising a liquid electrolyte.

In particular, the invention relates to the manufacture of a lithium-ion battery.

STATE OF THE PRIOR ART

Conventionally, a lithium battery is produced from a bag closed at all of its edges, except for one edge which remains open for the subsequent introduction of the liquid electrolyte. The bag is formed from a film, the ends of which are heat-sealed to obtain the welded edges.

Before the electrolyte is introduced into the partially closed bag, it is equipped with the battery electrodes, as well as one or more separators. For the introduction of the liquid electrolyte, a volumetric pipette is introduced, for example, introduced into the sachet, through the open edge. Once the filling has been carried out, a vacuuming operation is carried out before presenting the filled bag under the heating jaws of a heat-sealing tool, in order to seal the edge which has remained open.

However, the reliability of this waterproof closure remains perfectible. Indeed, during the filling of the liquid electrolyte and / or during the evacuation, there may be splashing or an ascent of electrolyte on the internal face of the flexible bag. This proves to be problematic during the subsequent step of thermo-welding the edge that remains open, since electrolyte particles are then liable to mix with the layer of molten film. It can thus create localized faults with bubbles, or even non-welded zones which may eventually generate privileged leak paths, capable of causing a loss of tightness during the life cycle of the battery.

STATEMENT OF THE INVENTION

To address this problem, the invention firstly relates to a method for filling a liquid electrolyte in a bag intended to form the outer envelope of a lithium battery in a bag, said method comprising the introduction of the electrolyte in an assembly comprising the closed sachet containing electrodes, the introduction being carried out by means of a cannula sealingly crossing a functional edge of the sachet formed by two superimposed and heat-sealed sachet ends, the cannula being interposed between the two ends of the bag and thermo-welded to them.

Thus, the invention cleverly provides for filling with a cannula integrated into the closed bag, which greatly limits the risks of leakage encountered in the prior art. Indeed, the bag being already closed at the time of filling, the risks of projection or rise of electrolyte are reduced to nothing. After filling, it then suffices to close the cannula to ensure complete sealing of the bag forming the outer envelope of the battery.

Preferably, the introduction of the liquid electrolyte is carried out by connecting an electrolyte supply device to one end of the cannula arranged outside said sachet, preferably via a syringe interposed between this end of the cannula and the delivery device. electrolyte supply.

The invention also relates to a method for manufacturing a lithium battery in a sachet, comprising the following steps:

- Production of an assembly comprising a closed bag containing electrodes, then implementation of the method for filling a liquid electrolyte in the closed bag; and

- obturation of the cannula, preferably in its portion outside said functional edge of the bag.

Preferably, after the implementation of the filling process and before the obturation of the cannula, the electrolyte supply device is disconnected and a step of electrical formation of the battery is carried out during which, and / or after which, gases generated by the reaction between the electrolyte and at least one of the electrodes during electrical formation, are stored in said syringe. The recovery of the gases before the final closure of the battery makes it possible to improve the overall electrochemical behavior of the battery, and to gain in reliability as well as in service life.

Preferably, the manufacturing process comprises a step of recovering the gases stored in the syringe, implemented using a purge device connected to said syringe.

Preferably, the step of closing the cannula is preceded by a step of cutting the latter. Alternatively, the step of closing the cannula is concomitant with a step of cutting the latter.

Preferably, the step of cutting the cannula is carried out so that the remaining end protrudes from the functional edge, over a length greater than 6 mm. Such a length makes it possible to reopen and then close the cannula during the life cycle of the battery, in order to carry out a gas purge and / or a new filling of liquid electrolyte. However, a shorter length could be chosen, for example between 1 and 6 mm. In this regard, it is indicated that closing the cannula in an area outside the functional edge makes it possible not to weaken the latter. This advantage is particularly advantageous when the obturation of the cannula is carried out by heat-welding, since the heat provided during this operation does not deteriorate the heat-welded connection between the two ends of the bag forming the functional edge.

Preferably, the step of producing the assembly includes forming the functional edge of the sachet, by placing the cannula between the two ends of the sachet, then by heat-sealing these three elements using a tool comprising heated jaws fitted with recesses for housing the cannula and parts of the bag ends in contact with this cannula during the heat sealing.

The invention also relates to an intermediate product defined by an assembly comprising a closed sachet containing electrodes, said assembly being intended for the manufacture of a lithium battery in sachet and said sachet being intended to be filled with a liquid electrolyte , the closed bag comprising a functional edge crossed in leaktight fashion by a cannula, said functional edge of the bag being formed by two superimposed and heat-sealed bag ends, and the cannula being interposed between the two bag and heat-sealed ends at these.

Preferably, the closed bag also contains at least one electrode separator.

Preferably, the closed bag is produced from a laminated film comprising an aluminum foil coated on its outer surface with a polyamide layer and coated on its inner surface with a polypropylene layer.

Preferably, the closed bag is produced from a film with a thickness of the order of 90 μm to 130 μm.

In order to best guarantee the seal between the cannula and the ends of the sachet during heat sealing, this cannula has an outside diameter less than or equal to five times the thickness of the film forming the closed sachet.

Finally, the cannula is flexible, preferably made of polypropylene.

Other advantages and characteristics of the invention will appear in the detailed non-limiting description below.

BRIEF DESCRIPTION OF THE DRAWINGS

This description will be made with reference to the accompanying drawings, among which;

- Figure 1 shows a schematic perspective view of a lithium battery in a bag, intended to be obtained by the implementation of a manufacturing method according to the invention;

- Figure 2 is a partially exploded view similar to that of Figure 1;

- Figure 3 is a sectional view of the film used for the production of the battery bag; and

FIGS. 4 to 12 schematize different stages of a method according to a preferred embodiment of the invention, aimed at the manufacture of the battery shown in FIGS. 1 and 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Firstly with reference to Figures 1 and 2, there is shown a lithium-ion battery in a bag, designated by the reference numeral 1. This battery 1, corresponding to an electrochemical cell, therefore comprises a flexible bag 3 which forms the outer shell of this battery. At its periphery, the bag is sealed. It contains an anode 2 which is extended by an anode connector 4 projecting outside the bag, as well as a cathode 6 which is extended by a cathode connector 8 also projecting outside the bag 3. The latter also contains a separator 10 and a liquid electrolyte 12.

As can be seen in FIG. 3, the bag 3 is produced from a laminated film comprising a screen in the form of aluminum sheet 14 coated on its outer surface with a polyamide layer 16, and coated on its inner surface of a polypropylene layer 18. The thickness of this film is of the order of 90 to 130 μ. The presence of polypropylene makes it possible to seal the ends of the sachet to form the edges of the latter, by heat welding. Indeed, by applying a temperature of the order of 180 to 190 ° C for a period of 3 to 5 seconds, it is possible to melt the polypropylene layer of the two ends of the sachet, since the melting point of the polypropylene is in the range of 150 to 165 ° C. At the same time, the polyamide outer layer is preserved since its melting temperature is of the order of 210 to 220 ° C.

The principle of thermo-welding the ends of the bag is used for the production of the assembly 20 shown in FIG. 4, this assembly constituting an intermediate product in the manufacture of the battery 1 shown in FIGS. 1 and 2. This assembly 20 includes the flexible bag 3 which is closed at its four edges and which encloses the separator and the electrodes. The assembly 20 is intended to be filled later with the liquid electrolyte, as will be detailed below. It has two edges 22 conventionally heat-welded, an edge 24 fitted with anode and cathode connectors 4, 8, as well as a functional edge 26 specific to the present invention.

Indeed, this functional edge 26 is equipped with a or a cannula 30 which passes through it in a sealed manner so as to protrude on the one hand outside the bag, and on the other hand inside the defined volume by the bag in which the electrodes are located as well as the separator. The outer part of the cannula has a mechanical connector 30a, intended to be subsequently connected to a syringe.

The cannula 30 is preferably flexible, made of polypropylene so as to ensure good chemical compatibility with the ends of the sachet, during heat sealing. It has for example an internal diameter of the order of 0.25 mm and an external diameter of the order of 0.52 mm. To limit the risks of vacuum between the ends of the bag and the outside surface of the cannula, the outside diameter of the latter is preferably less than or equal to five times the thickness of the film mentioned above.

The formation of the functional edge 26 of the bag is shown diagrammatically in FIGS. 4a and 4b. First, the cannula 30 is placed between the two ends of the bag 3 '. These two ends 3 'are in contact with each other outside their zone which marries the cannula 30. Junction zones reveal empty spaces 32 between the cannula and the two ends of the bag 3', these spaces being subsequently filled in during the heat-sealing step shown diagrammatically in FIG. 4b. For the implementation of this, a tool is used comprising heating jaws 34, supported externally on the outer layers of the two ends of the bag 3 '. To make the aforementioned spaces 32 disappear, the jaws 34 include recesses 36 for housing the cannula 30 and parts of the bag ends 3 ′ in contact with this cannula. The recesses 36 have a shape substantially complementary to that of the cannula.

Thus, when the jaws 34 are heated to a temperature of the order of 180 to 190 ° C., the shape of the recesses 36 makes it possible to fold the ends of the bag 3 'against the cannula at the level of the initial spaces 32, so as to create zones of molten material 40 ensuring the seal between the two superimposed ends 3 ′, and the cannula 30 interposed between these two ends. The chemical compatibility between the cannula and the ends of the bag 3 'makes it possible to obtain a high-performance thermal welding between these three elements, leading to a satisfactory seal.

Once the assembly 20 has been produced, a method of filling the closed bag 3 of this assembly is implemented, as shown diagrammatically in the figure.

5.

To do this, a plunger syringe 42 is mechanically connected to the connector 30a of the cannula 30, and the opposite end of the syringe is connected to a device 44 for supplying liquid electrolyte. During filling, the electrolyte flow rate through the cannula 30 is controlled, and fixed according to the capacity of the battery and the internal diameter of this cannula. The electrolyte leaving the inner end of the cannula is located directly in the volume defined by the closed bag 3, so that there is no risk of projection or significant rise of electrolyte in an area sensitive as in the prior art.

In this regard, it is noted that the introduction of the liquid electrolyte can be carried out in excess, so as to have a volume of electrolyte waiting in the syringe. This makes it possible, if necessary, to have additional injection during the subsequent stage of electrical training.

Preferably, after this step of introducing the electrolyte, the supply device 44 is disconnected from the syringe 42, which is temporarily closed using a plug 46 shown in FIG. 6. The closed end corresponds to the opposite end to that connected to the cannula connector 30a.

The plug 46 is held in place during the next stage of electrical formation of the battery, shown diagrammatically in FIG. 7. The electrical formation corresponds to the first electrical cycle of charge / discharge of the battery, carried out by connecting the connectors 4, 8 of the battery on a bench 50, in the same way as for a conventional battery. During this step, gases are generated generated by a reaction between the electrolyte and at least one of the electrodes, in particular the outer surface of the anode. The formation of these gases observed during the first hours of electrochemical operation of the battery are of the CO2, CO, CHU, C2H4, DMC, EC, DEC, etc. type. The presence of the syringe 42 thus makes it possible to constitute a reservoir in which these gases can be stored after having passed through the cannula 30, thus avoiding the risks of swelling generally generating an increase in the thickness of the battery as well as mechanical stresses at level of the edges of the bag. Once the electrical formation stage has been completed and the gases stored in the body of the syringe 42, a gas recovery stage is implemented using a purging device 52 shown in FIG. to do this, the stopper 46 is removed and the purge device 52 is fluidly connected to the end of the syringe released by this same stopper 46.

Then, a step of closing the cannula 30 is carried out as well as a step of cutting the latter, these two steps preferably being carried out concomitantly, using a tool with heating tongs 56 such as that shown in FIG. 10, intended to cut the cannula 30 at the fictitious line 58 represented in FIG. 9. Of course, the method can be implemented so that the step of cutting the cannula is carried out before the sealing step, without departing from the scope of the invention. In all cases, a heat-sealing operation is preferably carried out to close the cannula 30.

After the heated cutting of the cannula, the latter is closed in a sealed manner, as has been shown in FIG. 11 with the interior line 60 schematically showing the initial wall of opening of the cannula 30. At this stage, the the sachet thus becomes completely leaktight thanks to its heat-sealed edges and the closed cannula. In this regard, it is noted that the battery has been represented in an overall form of quadrilateral, but that other shapes can be adopted as an overall circular shape, without departing from the scope of the invention.

After cutting, the remaining end 30 ′ of the cannula projects from the functional edge 26 over a length “L” greater than 6 mm. A lower value could however be retained, even if the value of 6mm makes it possible to envisage, during the life cycle of the battery, to reopen then to close this cannula. Such a reopening can be implemented for example to carry out an additional purge of gases produced inside the sachet. It can also be envisaged for an addition of electrolyte, if necessary. In all cases, these additional gas purging and electrolyte addition operations are carried out according to the principles described above.

Of course, various modifications can be made by those skilled in the art to the invention which has just been described, only by way of nonlimiting examples.

Claims (15)

1. A method of filling a liquid electrolyte (12) in a bag (3) intended to form the outer envelope of a lithium battery in a bag (1), said method comprising the introduction of the electrolyte into a assembly (20) comprising the closed bag (3) containing electrodes (2, 6), the introduction being carried out by means of a cannula (30) sealingly crossing a functional edge (26) of the bag (3 ) formed by two bag ends (3 ') superimposed and heat-sealed, the cannula (30) being interposed between the two bag ends (3') and heat-welded thereto. 2. Method according to claim 1, wherein the introduction of the liquid electrolyte (12) is effected by connecting a device (44) for supplying electrolyte to one end (30a) of the cannula (30) arranged externally said bag (3), preferably via a syringe (42) interposed between this end of cannula (30a) and the electrolyte supply device (44). 3. Method for manufacturing a lithium battery in a sachet (1), comprising the following steps: - Production of an assembly (20) comprising a closed bag (3) containing electrodes (2, 6), then implementation of the method for filling a liquid electrolyte (12) in the closed bag (3), according to any of claims 1 and 2; and - obturation of the cannula (30), preferably in its portion external to said functional edge (26) of the sachet. 4. Method according to claim 3, characterized in that after the implementation of the filling method according to claim 2 and before the obturation of the cannula, the electrolyte supply device (44) is disconnected and it is carried out a step of electrical formation of the battery during which, and / or after which, gases generated by the reaction between the electrolyte (12) and at least one of the electrodes during electrical formation, are stored in said syringe (42). 5. Method according to claim 4, characterized in that it comprises a step of recovering the gases stored in the syringe, implemented using a purge device (52) connected to said syringe (42). 6. Method according to any one of claims 3 to 5, characterized in that the step of closing the cannula (30) is preceded by a step of cutting the latter. 7. Method according to any one of claims 3 to 5, characterized in that the step of closing the cannula (30) is concomitant with a step of cutting the latter. 8. Method according to claim 6 or claim 7, characterized in that the step of cutting the cannula (30) is carried out so that the remaining end protrudes from the functional edge (26), over a length (L ) greater than 6 mm. 9. Method according to any one of claims 3 to 8, characterized in that the step of producing the assembly (20) comprises forming the functional edge (26) of the sachet, by placing the cannula (30) between the two bag ends (3 '), then by heat-sealing these three elements using a tool comprising heating jaws (34) equipped with recesses (36) for housing the cannula (30) and parts of the bag ends (3 ') in contact with this cannula during heat sealing. 10. An assembly (20) comprising a closed sachet (3) containing electrodes (2, 6), said assembly being intended for the manufacture of a lithium battery in a sachet (1) and said sachet (3) being intended to be filled with a liquid electrolyte (12), characterized in that the closed bag (3) comprises a functional edge (26) crossed in a sealed manner by a cannula (30), said functional edge of the bag being formed by two ends of the bag (3 ') superimposed and heat-sealed, and the cannula (30) being interposed between the two ends of the bag (3') and heat-welded thereto. 11. An assembly according to claim 10, characterized in that the closed bag (3) also contains at least one electrode separator (10). 12. The assembly of claim 10 or claim 11, characterized in that the closed bag (3) is made from a laminated film comprising an aluminum foil (14) coated on its outer surface with a polyamide layer (16) and coated on its inner surface with a polypropylene layer (18). 13. An assembly according to any one of claims 10 to 12, characterized in that the closed bag (3) is produced from a film with a thickness of the order of 90 μm to 130 μm. 14. An assembly according to any one of claims 10 to 13, characterized in that the cannula (30) has an outer diameter less than or equal to five times the thickness of the film forming the closed bag (3). 15. Assembly according to any one of claims 10 to 14, characterized in that the cannula (30) is flexible, preferably made of polypropylene. S.61302