FR3158387A1 - Pressure application device for an electric battery - Google Patents

Abstract

A pressure application device (9) for an electric battery comprising an electrochemical cell (2), said device (9) comprising a first compression plate (11) and a second compression plate (13), said first and second plates (11, 13) being adapted to be inserted so as to frame the electrochemical cell (2), characterized in that it comprises at least one assembly (15) comprising: - a first notched element (16), - a second notched element (23), and movable in translation in its longitudinal direction, said first and second elements (16, 23) being arranged together so that said second element (23) is held to the first element (16), and - a spring (33) axially oriented in the longitudinal direction of said notched elements, said at least one assembly (15) being able to be installed so that the spring (33) is able to bear between said second notched element (23) and the first or second plate (11, 13), and said spring (33) being sized to manage the volume variations of the cell (2) during a charge and discharge cycle, and to cause said second notched element (23) to mesh with said first notched element (16) in one step after a predetermined number of cycles. Abstract figure: Figure 2

Description

Pressure application device for an electric battery

The present invention relates to a pressure application device for an electric battery comprising at least one electrochemical cell.

When charging a Li-ion battery with a silicon-containing electrode, lithium will form silicon alloys with the formula Li _x Si. The formation of these alloys results in an increase in the volume of the Si particles, which can reach up to 300% of the initial volume of the silicon particles. When discharging the Li-ion battery, the Li _x Si alloys are delithiated, thus causing a decrease in the size of the silicon particles. At the scale of the silicon electrode and the cell, strong, quasi-reversible volume variations, similar to breathing, will therefore occur during the battery charge and discharge cycles. These volume variations over the life of the battery (successive charges and discharges) will cause strong mechanical stresses within the Li-ion battery. The Si particles can fracture, become detached from the current collector and/or become electronically isolated from the percolating network of the electrode. These phenomena will then lead to a degradation of the battery performance.
In addition, throughout the life of the cell, parasitic reactions will occur, generating an irreversible increase in volume this time, and therefore premature aging of the battery, with swelling being observed at the cell level.

Patent application WO2023/046389 A1 describes a device for clamping electrochemical battery cells, comprising deformable materials to form various deformable zones, capable of handling cell volume variations caused by charge/discharge cycles and by cell aging. More particularly, the clamping compression device comprises a clamping body installed around and against the cell assembly, and a fixing body for fixing the clamping body to the battery frame. The clamping device further comprises a clamping joint connecting the clamping body and the fixing body.

The clamping joint is designed so that during cell swelling, the clamping body is moved towards the fixing body and the clamping joint is moved in a defined manner. The clamping joint has two flexible components, one reversible and one irreversible, to manage the volume variations related to battery aging but also to battery charging/discharging. The volume variation related to the battery charging and discharging cycle is also absorbed by the clamping body in a reversible elastic flexibility zone.

However, the device described in this patent application may pose safety problems in that the deformation of the materials may depend on the temperature. In addition, the elements of this device have areas of flexibility which weaken them, so they can break over time. It is therefore necessary to ensure constant monitoring.

In addition, the described deformable device is quite bulky since it requires several different deformation zones to manage the swelling of the cells. This device is also difficult to implement in pre-existing batteries or to adapt according to the number of electrochemical cells.

There is therefore a need for a less bulky, easier to implement clamping compression device compared to the prior art, and not presenting any safety problems.

For this purpose, a pressure application device is proposed for an electric battery comprising at least one electrochemical cell and a frame in which the at least one cell is installed, said device comprising a first compression plate and a second compression plate, said first and second plates being adapted to be inserted between the frame and the at least one electrochemical cell so as to frame the at least one electrochemical cell. The pressure application device comprises at least one assembly comprising:
- a first fixed, elongated notched element, comprising notches arranged in its longitudinal direction,
- a second notched element of elongated shape comprising notches arranged in its longitudinal direction, and movable in translation in its longitudinal direction, said first and second elements being arranged together in their longitudinal directions so that said second element is held to the first element by engagement of at least one of its notches with at least one notch of the second element, and
- a spring axially oriented in the longitudinal direction of said notched elements, said at least one assembly being able to be installed between the frame of the battery and the first plate or the second plate and so that the spring is able to bear between said second notched element and the first or the second plate, and said spring being dimensioned in a predetermined manner to manage the volume variations of the at least one cell during a charge and discharge cycle, and to cause said second notched element to mesh with a gear pitch equal to at least one notch with said first notched element after a predetermined number of charge and discharge cycles of the at least one cell.

This device thus makes it possible to apply (almost) constant pressure to at least one electrochemical cell to limit and compensate for its volume variations.

In fact, the spring is sized to compensate for the variation in volume of the at least one cell during the charge and discharge cycles. The spring therefore compresses slightly when the volume of the at least one cell increases while it relaxes when the volume of the at least one cell decreases.

In addition, the combination of the spring and the first notched element and the second notched element also makes it possible to compensate for the variation in volume, in particular its increase, during the aging of the at least one cell. Although the volume of a cell varies during the charge and discharge cycles, its volume increases irreversibly during its aging. This increase in volume is thus compensated by the second notched element which is meshed with one step in the first notched element after a determined number of cycles. The gearing thus makes it possible to allocate a larger space to the at least one cell.

Preferably, the first notched element has a generally cylindrical and hollow shape, having an open face, the second notched element has a generally cylindrical and hollow shape, having an open face and a stop axially opposite said open face, said second notched element being inserted by force into said first notched element and held in said first element by engagement of at least one respective notch of said first and second notched elements, and the spring being installed inside said second notched element between the open face and the stop of said second element in the axial direction of said second element.

The respective longitudinal direction of a notched element corresponds to the axial direction of its cylindrical shape.

Advantageously, the first notched element has a plurality of internal notches extending in the longitudinal direction of said first element and over at least part of its internal periphery, and,
the second notched element has a plurality of external notches extending in the longitudinal direction of said second element and over at least part of its external periphery, said second notched element being held to said first notched element by engagement of at least one of its internal notches with at least one external notch of said second element.

Preferably, the spring is a compression spring sized according to a predefined stiffness to manage the volume variations of the at least one cell during a charge and discharge cycle, while allowing the meshing between the notched elements to manage the aging cycles.

The parameter relating the applied force to the elongation of the spring is called the stiffness, usually denoted k. This constant k is established according to the number of coils, the diameter of the spring wire, the average diameter of the coils, the length of coils available, and other coefficients linked to the material of the spring wire.

Advantageously, the pressure application device comprises a plurality of said assemblies, preferably distributed symmetrically on either side of the first and second compression plates.

The number of sets used thus depends on the dimensions of the cells. It is chosen so as to absorb the variations in volume of at least one cell along its entire length.

The invention also relates to an electric battery comprising at least one electrochemical cell and a frame in which the at least one cell is installed. The electric battery further comprises a pressure application device as described above.

Advantageously, the first notched element of said assembly is fixed by attachment to said frame.

Preferably, the electric battery comprises a plurality of electrochemical cells stacked between the first plate and the second compression plate substantially parallel to each other, the pressure application device applying pressure in the direction of the stacking.

Advantageously, the at least one electrochemical cell comprises a flexible envelope in which is arranged at least one elementary unit comprising a positive electrode composed of a positive current collector and at least one layer of active materials and a negative electrode composed of a negative current collector and at least one layer of active materials, and a separator between said stacked positive and negative electrodes.

The invention also relates to a motor vehicle comprising at least one electric battery as described above.

Other features and advantages of the invention will emerge from reading the description given below of a particular embodiment of the invention, given for informational purposes but not as a limitation, with reference to the appended drawings in which:

FIG. 1 is a schematic perspective view from the side and from above of an electric battery according to the invention.

FIG. 2 is a schematic, exploded view of elements of the battery according to the invention illustrated in FIG. 1 .

FIG. 3 is an exploded schematic view, detailing a set of certain elements represented in the FIG. 2 .

FIG. 4 is a schematic view, in longitudinal section, illustrating in detail elements of the FIG. 2 in a first situation (start of battery life and charge state at 0%).

FIG. 4 is a schematic view in longitudinal section, illustrating in detail elements of the FIG. 2 in a second situation (start of battery life and 100% charge state).

FIG. 4 is a schematic view in longitudinal section, illustrating in detail elements of the FIG. 2 in a third situation (end of battery life and charge state at 0%).

FIG. 4 is a schematic view in longitudinal section, illustrating in detail elements of the FIG. 2 in a fourth situation (end of battery life and 100% charge status).

There FIG. 1 illustrates an electric accumulator battery 1 comprising a plurality of electrochemical cells 2. The electrochemical cell allows chemical energy to be reversibly converted into electrical energy. The number of cells required depends on the desired battery capacity.

The electrochemical cell 2 is a pouch-type cell. It comprises a flexible envelope 3 called a protective film. The flexible envelope 3 is made of a flexible material so as to tightly envelop the components of the cell. The envelope 3 may be a complex assembly of aluminum layers and polymer layers including at least one thermofusible inner surface polymer layer. In this case, it is closed by thermal welding to fuse the polymer layers.

Inside the envelope 3, the cell 2 comprises at least one elementary unit (not shown in the figures) comprising a positive electrode, a negative electrode and a separator between said stacked positive and negative electrodes. The whole is soaked in an electrolyte allowing ionic conduction. The elementary unit is multiplied as many times as necessary to obtain the desired cell capacity.

The positive electrode, also called cathode, is composed of an electrically conductive material, called positive current collector or cathode current collector, as well as a layer of active, porous materials, made up of electrochemically active materials for energy storage, as well as additive materials allowing electrical conductivity, material cohesion and adequate morphology.

The negative electrode, also called anode, is composed of an electrically conductive material, called negative current collector, or anode current collector, as well as a layer of active, porous materials, made up of electrochemically active materials for energy storage, as well as additive materials allowing electrical conductivity, material cohesion and adequate morphology (electro-active and additives).

The battery 1 further comprises a frame 4 in which the electrochemical cells 3 are installed and a casing 5 so as to close the battery and protect the cells 3. The frame and the casing can be made of a metallic material such as aluminum or of a polymer material.

The battery 1 also includes a positive termination 6 and a negative termination 7 joining the respectively positive and negative terminals of the cells. The ends of the positive 6 and negative 7 terminations are accessible outside the battery 1 through two holes 8 present on the casing 5 so as to be able to electrically connect the battery to an electrical circuit.

The battery 1 also comprises a pressure application device 9 according to the invention capable of applying pressure to the cells 2. This device is held at the frame 4 of the battery 1 by a plurality of screws 10 passing through said frame 4.

As illustrated on the FIG. 2 , the pressure application device 9 comprises a first compression plate 11 and a second compression plate 13 installed on either side of the electrochemical cells, said plates extending in the direction of the length of the cells.
The first and second compression plates 11, 13 have substantially the same dimensions as those of the cells 2.

The cells 2 are thus inserted between the first and second plates 11, 13 while being parallel to the first and second plates 11, 13 so that the first and second plates frame the cells 2.

The device 9 further comprises eight assemblies 15, composed of notched elements and a spring (see FIG. 3 ), distributed symmetrically on either side of the first and second compression plates 11, 13. Four sets are distributed along the first compression plate 11 between the first plate 11 and the frame 4 while the other four sets are distributed along the second compression plate 13 and between said second plate 13 and the frame 4.

However, the number of sets is not limited to eight, it can be chosen according to the dimensions of the cells, in particular their length, or according to the arrangement of the battery for example.

As illustrated on the FIG. 3 , the assembly 15 comprises a first notched element 16, elastically deformable. This first notched element 16 is of elongated shape, generally cylindrical and hollow, and it is fixed in the device. It has an open face 17 and a closed face 18. The closed face 18 rests on the frame 4 while the open face 17 is oriented towards the first or second compression plate 11, 13.

The closed face 18 of said first notched element 16 has an orifice 19 adapted to receive a screw 10 to hold the application device 9 in the frame 4 of the battery 1, more particularly to keep said first notched element 16 fixed.

The first notched element 16 further has a plurality of internal notches 21 arranged along its longitudinal direction (which corresponds to its axial direction), and in particular along its internal circumference. The grooves of the notches are oriented along the internal circular circumference of the cylinder.

Said first notched element 16 comprises a cylindrical wall with a circular section comprising cutouts between which lamellae are formed, improving the elasticity of said wall, which contributes to the elastically deformable character in addition to the fact that said element is hollowed out to confer a certain elasticity to the metal wall.

The plurality of internal notches 21 is distributed on the internal face of said slats.

The assembly 15 also comprises a second notched element 23. The second notched element 23 is of elongated shape and is movable in translation in its axial direction. It is in particular of hollow cylindrical shape with an orifice 25 passing through its center. It has an open face 27 and a stop 29 axially opposite the open face 27.

The second notched element 23 has a plurality of external notches 31 along its longitudinal direction (which is also its axial direction), extending in particular along its external circumference. The plurality of external notches 23 is placed over the entire external circumference according to the example. The grooves between the notches are oriented along the external circular circumference of the cylinder.

The second notched element 23 and the first notched element 16 are arranged together in their longitudinal directions, in other words they are coaxial. The second notched element 23 forms a notched core which is inserted at least partly in particular into the first notched element 16.

The second notched element 23 is held to the first notched element 16 by engagement of at least one of its internal notches 21 with at least one external notch 31 of the second notched element 23.

The number of internal 21 and external 31 notches can be determined according to the characteristics of the cells 2, in particular their size, and more particularly their thickness changes over time.

In the illustrated example, the second element 23 has eight external notches 31 just like the first element 16 which has eight internal notches 21.

The assembly 15 further comprises a compression spring 33. Said spiral spring 33 is axially oriented in the longitudinal direction of the first and second notched elements 16, 23. The spring 33 is installed inside the second notched element 23 between the open face 27 and the stop 29, it is in particular installed against the stop 29.

Such an assembly 15 has a diameter of approximately 100 millimeters, however its size may vary depending on the dimensions of the cells 2. This diameter corresponds to the diameter of the first notched element which is the largest diameter of the assembly.

The spring 33 is dimensioned in a predetermined manner to manage both the variations in cell volume during a charge and discharge cycle, and during “aging”. For this, the stiffness of the spring is defined according to the characteristics of the cells 2.

In reference to the FIG. 4 has FIG. 4 , the spring 33 allows to absorb the variations in the volumes of the cells between their charge and their discharge, at each cycle (similar to a breathing cycle). Thus, it contracts, its turns being almost joined, when the cells are charged as illustrated in the FIG. 4 And FIG. 4 , for which the battery state of charge (SOC) is 100%, and it relaxes, its turns being a little more disjointed, when the cells discharge as illustrated in the FIG. 4 And FIG. 4 for which the battery state of charge (SOC) is 0%.

At the same time, after a predetermined number of charge and discharge cycles of the cells 2, for example 100 cycles defining an aging cycle, the second element 23 will mesh by one step, or by one notch with a notch of the first notched element 16 at each aging cycle, as illustrated between the start of life of the battery in the figures FIG. 4 Or FIG. 4 and the end of battery life in the figures FIG. 4 Or FIG. 4 , after several aging cycles. The FIG. 4 illustrates the assembly 15 mounted between the frame 4 and a compression plate, at the beginning of the life of the cells, the state of charge (SOC) being 0%, while the FIG. 4 illustrates set 15 at the end of cell life, with the state of charge (SOC) at 0%.

Thus, at the start of the battery's life, the first notched element is held by force in the second notched element and by engagement of an internal notch with an external notch, then at the end of a first aging cycle, it is held by two internal notches 21 to two external notches 31, and so on during aging until the end of the battery's life.

The displacement of the second element 23 by one notch is due to the increase in volume of the cells due to their aging. Thus, after a predetermined number of charge/discharge cycles, the increase in volume of the cells will make it possible to obtain sufficient force from the springs 33 against the compression plates to thus push, in axial translation, the notched core 23 into the first notched element 16 and make it mesh by an additional notch with the notches of said first notched element, the elasticity of the wall of said first notched element 16 also allowing the second notched element 23 to move forward by force inside.

For example, after about a hundred charge/discharge cycles (i.e. one aging cycle), each spring has joined turns. The force exerted by the spring on the notched core 23 is then greater than the resistance of the notches already meshed. The notched core 23 then jumps one notch and frees up space for the cells until the next 100 cycles, and so on.

The number of charge/discharge cycles predetermined for advancing a step (equal to one notch) can be chosen according to the characteristics of the cells used for example.

Combining springs with a notched side adjustment mechanism allows the pressure on the cells to be kept almost constant throughout the life of the cells.

The pressure application device 9 thus makes it possible to improve the performance of the cells, in particular their lifespan, in particular by increasing the number of charge/discharge cycles of the cells. It also offers a unique mechanical system to manage the two causes of variation in cell volume, which are respiration and aging. The device can be easily adjusted to a given battery by adjusting the number of assemblies (notched elements, springs). In addition, this mechanical system is advantageously very compact.

Claims (10)

Pressure application device (9) for an electric battery (1) comprising at least one electrochemical cell (2) and a frame (4) in which the at least one cell (2) is installed, said device (9) comprising a first compression plate (11) and a second compression plate (13), said first and second plates (11, 13) being adapted to be inserted between the frame (4) and the at least one electrochemical cell (2) so as to frame the at least one electrochemical cell (2),
characterized in that it comprises at least one assembly (15) comprising:
- a first fixed, elongated notched element (16), comprising notches (21) arranged in its longitudinal direction,
- a second notched element (23) of elongated shape comprising notches (31) arranged in its longitudinal direction, and movable in translation in its longitudinal direction,
said first and second elements (16, 23) being arranged together in their longitudinal directions so that said second element (23) is held to the first element (16) by engagement of at least one of its notches (21) with at least one notch (31) of the second element (23), and
- a spring (33) axially oriented in the longitudinal direction of said notched elements,
said at least one assembly (15) being able to be installed between the frame (4) of the battery (1) and the first plate (11) or the second plate (13) and so that the spring (33) is able to bear between said second notched element (23) and the first or second plate (11, 13), and
said spring (33) being dimensioned in a predetermined manner to manage the volume variations of the at least one cell (2) during a charge and discharge cycle, and to cause said second notched element (23) to mesh with a gear pitch equal to at least one notch with said first notched element (16) after a predetermined number of charge and discharge cycles of the at least one cell (2). Pressure application device (9) according to claim 1, characterized in that:
- said first notched element (16) has a generally cylindrical and hollow shape, having an open face (17),
- said second notched element (23) has a generally cylindrical and hollow shape, having an open face (27) and a stop (29) axially opposite said open face (27), said second notched element (23) being force-fitted into said first notched element (16) and held in said first element (16) by engagement of at least one respective notch (21, 31) of said first and second notched elements (16, 23),
- and said spring (33) being installed inside said second notched element (23) between the open face (27) and the stop (29) of said second element (23) in the axial direction of said second element (23). Pressure application device (9) according to claim 1 or 2, characterized in that said first notched element (16) has a plurality of internal notches (21) extending in the longitudinal direction of said first element (16) and over at least part of its internal periphery, and,
said second notched element (23) has a plurality of external notches (31) extending in the longitudinal direction of said second element (23) and over at least part of its external periphery, said second notched element (23) being held to said first notched element (16) by engagement of at least one of its internal notches (21) with at least one external notch (31) of said second element (23). Pressure application device (9) according to any one of claims 1 to 3, characterized in that the spring (33) is a compression spring sized according to a predefined stiffness to manage the volume variations of the at least one cell (2) during a charge and discharge cycle. Pressure application device (9) according to any one of claims 1 to 4, characterized in that it comprises a plurality of said assemblies (15), preferably distributed symmetrically on either side of the first and second compression plates (11, 13). Electric battery (1) comprising at least one electrochemical cell (2) and a frame (4) in which the at least one cell (2) is installed, characterized in that it further comprises a pressure application device (9) according to any one of the preceding claims. Battery (1) according to claim 6, characterized in that said first notched element (16) of said assembly (15) is fixed by fixing to said frame (4). Battery (1) according to one of claims 6 or 7, characterized in that it comprises a plurality of electrochemical cells (2) stacked between the first compression plate (11) and the second compression plate (13) substantially parallel to each other, the pressure application device (9) applying pressure in the direction of the stacking. Battery (1) according to any one of claims 6 to 8, characterized in that the at least one electrochemical cell (2) comprises a flexible envelope (3) in which is arranged at least one elementary unit comprising a positive electrode composed of a positive current collector and at least one layer of active materials and a negative electrode composed of a negative current collector and at least one layer of active materials, and a separator between said stacked positive and negative electrodes. Motor vehicle comprising at least one electric battery (1) according to one of claims 6 to 9.