Method for managing the pressure applied to lithium-ion batteries
Patent Information
- Application Number
- FR2021013874
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2021-12-17
- Publication Date
- 2025-03-14
- Estimated Expiration
- 2041-12-17
Smart Images
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Abstract
Description
Title of the invention: Method for managing the pressure applied to lithium ion batteries
[0001] The present invention relates to a method for managing the pressure applied to lithium ion batteries.
[0002] When charging the Li-ion battery, the lithium will form silicon alloys of the formula LixSi with the silicon. The formation of these alloys leads to 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 LixSi alloys are delithiated, thus leading to 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 during 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 be electronically isolated from the percolating network of the electrode.These phenomena will then lead to a degradation of the battery's performance. In addition, parasitic reactions will occur, generating an irreversible increase in volume, and therefore premature aging of the battery.
[0003] Application DE102009035482 A1 describes a lithium-ion electric battery for a motor vehicle comprising a plurality of battery cells fixed between two end plates and forming a cell stack. More particularly, the lithium-ion battery comprises several battery cells, inserted between two plates thus forming a cell stack. A unit makes it possible to apply a pressure load to the cell stack, in a stacking direction by means of a spring and using an active actuator. The actuator is controlled as a function of the characteristic lifetime / pressure diagram, or as a function of the measured temperature and / or pressure values in the cell stack, said values depending on the charge / discharge cycles.
[0004] A method according to the invention makes it possible to monitor the volume variations of the Si particles during the various charging and discharging cycles of an electric battery, by applying an optimized pressure at each instant. As a result, the performance of the Li-ion battery is preserved over time, and the aging of said battery is significantly slowed down.
[0005] The subject of the invention is a system for applying variable pressure to a electric battery comprising at least one electrochemical cell, inserted between a first end plate and a second end plate parallel to each other.
[0006] According to the invention, the system comprises a first assembly comprising a first actuating wall extending parallel to the two end plates and located opposite the first end plate, said first assembly comprising at least one first spring inserted between the first actuating wall and the first end plate, said first actuating wall being able to move towards or away from the first end plate to exert pressure on said first plate, under the effect of the movement of a connecting rod extending parallel to the first actuating wall and moved by an actuator, said connecting rod being connected to said first actuating wall by at least one cam, a first end of which is mounted in rotation on the connecting rod, and a second end of which is mounted in rotation about an axis of rotation secured to a fixed wall parallel to the first actuating wall,said second end being in abutment against the first actuating wall. The principle of a method according to the invention is to be able to exert a homogeneous pressure on one of the two end plates of the electric battery by means of at least one spring, which can be more or less compressed depending on the movement of the link. Indeed, the movement of the link in one direction will cause a movement of said at least one cam in a first direction, which will bring the first actuating wall closer to the first end plate, causing a compression of said at least one spring which will then exert an increased pressure on said first end plate. A movement of the link in an opposite direction will cause a movement of said at least one cam in a second direction, which will move the first actuating wall away from the first end plate,causing a relaxation of said at least one spring which will then exert less pressure on this first end plate. Preferably, the connecting rod is a straight and elongated rod, and the actuator is configured to allow this rod to be moved in translation along a longitudinal axis of said rod, and this, in both directions. In a system according to the invention, the first actuating wall is inserted between the connecting rod and the first end plate, and said at least one cam is inserted between the connecting rod and the first actuating wall. Preferably, the first system comprises a plurality of springs, the number of which is greater than five, and a plurality of cams, the number of which is greater than five. According to a particular embodiment, there are as many cams as there are springs.
[0007] According to a possible characteristic of the invention, the connecting rod is an elongated rod, the actuator moving said connecting rod in translation along a longitudinal axis of this link. The movement of the link under the effect of the actuator, is carried out along an axis which is parallel to the first actuating wall and to the first end plate, and the movement of the first actuating wall relative to the first end plate is carried out along an axis which is perpendicular to the axis along which the link moves.
[0008] According to a possible characteristic of the invention, each cam comprises a rod connecting the first end to the second end, said second end comprising an elongated segment, which is placed around the axis of rotation. The second end materialized by the elongated segment is fixed relative to the rod of the cam. The axis of rotation is placed at one end of the elongated segment, so that the rod of the cam is located on one side of this axis of rotation and the elongated segment is located on the other side of said axis of rotation. A movement of the connecting rod will cause a rotation of the rod of the cam, which will then cause a rotation of the elongated segment due to the presence of the axis of rotation. Since this elongated segment is in contact with the first actuating wall, the rotation of the elongated segment of the cam will cause a movement of the actuating wall in one direction or the other depending on the direction of rotation of the elongated segment.
[0009] According to a possible characteristic of the invention, the system comprises a computer intended to control the actuator to move the link in the desired direction and with the desired amplitude, so as to place the first actuating wall at a given distance from the first end plate, with the aim of compressing each first spring more or less to exert the desired pressure on said first end plate. This computer is programmed so as to essentially take into account a charging or discharging phase of the electric battery. Depending on said phase, the computer will trigger the actuator at a precise moment, which will cause a movement of the first actuating wall via the link and the cam, to increase or decrease the pressure exerted by said at least one first spring on the first end plate.
[0010] According to a possible characteristic of the invention, the system comprises a second assembly comprising a second actuating wall extending parallel to the two end plates and located opposite the second end plate, said second assembly comprising at least one second spring inserted between the second actuating wall and the second end plate, the direction of the forces exerted by said at least one second spring being parallel to the direction of the forces exerted by said at least one first spring, said second actuating wall bearing against a fixed wall which is parallel to said second actuating wall. This second assembly makes it possible to homogenize the general pressure exerted on the electric battery by the springs, thanks to the presence of the two assemblies each capable of exerting pressure on each side of the electric battery.
[0011] According to a possible characteristic of the invention, the system comprises twelve first springs inserted between the first actuating wall and the first end plate and twelve second springs inserted between the second actuating wall and the second end plate.
[0012] According to a possible characteristic of the invention, the first springs are aligned along an axis which is parallel to the end plates and the second springs are also aligned along an axis which is parallel to said end plates. In this way the first actuating wall and the second actuating wall will exert a homogeneous pressure respectively on the first end plate and on the second end plate.
[0013] According to a possible characteristic of the invention, each first spring and each second spring are constituted by Belle Ville washers. Alternatively, other types of spring can be used, such as for example spiral springs or compression foam.
[0014] According to a possible characteristic of the invention, the system comprises a fixed frame enclosing the electric battery, the first actuating wall, the second actuating wall, said at least one first spring, said at least one second spring, the second actuating wall being in contact with a second flat wall of the frame and said at least one axis of rotation around which the second end of said at least one cam is mounted being secured to a first flat wall of the frame which is parallel to said second flat wall, the connecting rod being located behind said first flat wall of the frame while being placed outside of said frame.
[0015] Another subject of the invention is a method of using a system according to the invention during a cycle comprising a charging phase then a discharging phase of a Li-ion electric battery.
[0016] According to the invention, the method comprises the following steps: - a starting step for which the cells are at dimension xl and the system exerts a force Fl, - a charging stage of the electric battery for which the force exerted by the system increases up to a value F2 which is greater than Fl, because the battery cells have expanded during the charging phase and are now at a dimension x2 which is greater than xl, - a step of starting a discharge of the battery comprising a step of prior activation of the system controlled by the computer for which the connecting rod is translated in a direction causing a rotation of the cams in a first direction which will bring the first actuating wall closer to the first end plate, said system then instantly exerting a force F3 on the battery, which is greater than the force F2, - a battery discharge end stage for which the system applies a force F4 to the battery which is less than the force F3, this force F4 applied at the end of discharge being due to the cells which have lost volume during this discharge phase, - a step of activating the system controlled by the computer for which the connecting rod is translated in an opposite direction causing a rotation of the cams in a second direction which will move the first actuating wall away from the first end plate, said system then instantly exerting a force Fl on the battery, which is less than the force F4, to return the cells to their pre-charge pre-stressed state.
[0017] It is understood that the step of charging the electric battery can be triggered for any initial state of charge of the battery, which is not necessarily zero. Similarly, the step of discharging the battery can cease regardless of the state of discharge of the battery, which is not necessarily zero.
[0018] A detailed description of a preferred embodiment of a variable pressure application system according to the invention is given below with reference to the following figures:
[0019] [Fig.l] represents a schematic view of a system for applying variable pressure to an electric battery according to the invention, the cells being at the side of xl and the system exerting a force Fl,
[0020] [Fig.2a] represents a diagram illustrating an example of the force applied to the cells of an electric battery over time, during a charging and then discharging phase of said battery,
[0021] [Fig.2b] represents a diagram illustrating an example of a variation of the width of a cell of a battery over time, during a phase of charging then discharging of said battery,
[0022] [Fig.3] represents a schematic view of a system according to the invention while the electric battery is at the end of charging, the cells being at the dimension x2 > xl and the force exerted is the force F2 > Fl due to the dimensioning of the cells,
[0023] [Fig.4] represents a schematic view of a system according to the invention for which we exert a force F3 > F2 on the cells, which are at the x2 coast, while these are at the beginning of discharge,
[0024] [Fig.5] represents a schematic view of a system according to the invention while the electric battery is at the end of discharge, the cells having returned to the xl rating and said system exerting a force F4,
[0025] [Fig.6] represents a schematic view of a system according to the invention for which the actuator decreases the pressure on the cells while they are at the beginning of load, said cells being at the dimension xl and the system applying a force Fl,
[0026] [Fig.7a] represents a diagram illustrating an example of the force applied to the cells of an electric battery over time, during a charging and then discharging phase of said battery, said cells having widened through aging, to be at the size x3 instead of xl,
[0027] [Fig.7b] represents a diagram illustrating an example of a variation of the coast of the cells of a cell of a battery over time, during a phase of charging then discharging of said battery, said cells having widened through aging, to be at the size x3 instead of xl,
[0028] [Fig.8] represents a schematic view of a system according to the invention while the electric battery is at the start of charging, the cells being at the x3 rating and a force of Fl is exerted,
[0029] [Fig.9] represents a schematic view of a system according to the invention while the electric battery is at the end of charging, the cells being at the x4 dimension greater than x3 the force then exerted is the force F2 greater than Fl due to the taking of dimension of the cells,
[0030] [Fig. 10] represents a schematic view of a system according to the invention for which a force F3 greater than F2 is exerted on the cells, which are at the x4 dimension, while these are at the beginning of discharge,
[0031] [Fig. 11] represents a schematic view of a system according to the invention while the electric battery is at the end of discharge, the cells having returned to the rating of x3 and said system exerting a force F4,
[0032] [Fig. 12] represents a schematic view of a system according to the invention for which the actuator reduces the pressure on the cells while these are at the start of charging, said cells being at the x3 dimension and the system applying a force Fl,
[0033] An electric battery 2 is made up of a series of several Li-ion cells 3 which are perfectly aligned while being in contact with each other. This electric battery 2 comprises a first end plate 4 and a second end plate 5 enclosing the cells 3 of said electric battery 2. Schematically, these two end plates 4, 5 have substantially the same dimensions as those of the cells 3, said cells 3 being inserted between these two end plates 4, 5 while being parallel to said end plates 4, 5.
[0034] A system 1 for applying variable pressure according to the invention is capable of applying pressure to the first end plate 4 and to the second end plate 5, and comprises: -a frame 6, -a first assembly 7 comprising a first actuating wall 8, several cams 9, several first springs 10, a connecting rod 11, an actuator 12 capable of moving said connecting rod 11 and a computer 13 intended to control said actuator 12 in depending on the phase in which the battery 2 is located, namely charging or discharging phase, and start of life until end of life of the battery - a second assembly 40 comprising a second actuating wall 14 and several second springs 15.
[0035] The connecting rod 11 is represented by an elongated rectilinear rod, and the actuator 12, depending on the instruction it receives from the computer 13, is able to move said connecting rod 11 in translation along a longitudinal axis of said connecting rod 11, in one direction or the other.
[0036] Each cam 9 comprises a first end 16 which is mounted articulated on the connecting rod 11, and a second end 17 comprising an elongated segment, said first end 16 and said second end 17 being connected by a connecting rod 18. The second end 17 is connected to the connecting rod 18 in a fixed manner, so that the elongated segment is inclined relative to said connecting rod 18. The elongated segment of the second end 17 of each cam 9 passes around a connecting axis which is secured to a first wall 19 of the frame 6, which is parallel to the first actuating wall 8 and to the first end plate 4 of the electric battery 2.
[0037] The first actuating wall 8 is planar and is arranged parallel to the first end plate 4 of the battery 2 and opposite it. A series of several first springs 10 is inserted between the first end plate 4 of the electric battery 2 and the first actuating wall 8, said first springs 10 possibly being twelve in number, for example. These first springs 10 are aligned along the first actuating wall 8 and along the first end plate 4 of the battery 2. The connecting rod 11 extends parallel to the first actuating wall 8 and to the first end plate 8 of the electric battery 2, so that said first actuating wall 8 is placed between said connecting rod 11 and said first end plate 4.
[0038] The second actuating wall 14 is planar and is arranged parallel to the second end plate 5 of the electric battery 2 and opposite it. A series of several second springs 15 is inserted between the second end plate 5 of the battery 2 and the second actuating wall 14, said second springs 15 possibly being twelve in number, for example. These second springs 10 are aligned along the second actuating wall 14 and along the second end plate 5 of the electric battery 2. Under the effect of the second springs 15 the second actuating wall 14 is pressed against a second wall 20 of the frame 6 which is parallel to the first wall 19 of the frame 6 on which the rotation axes of the cams 9 are fixed. This second wall 20 of the frame 6 is parallel to the second actuating wall 14 and to the second end plate 5 of the battery 2. In other words, the second actuating wall 14 is inserted between the second wall 20 of the frame 6 and the second end plate 5 of the battery 2.
[0039] The first springs 10 and the second springs 15 may for example be constituted by Belleville washers. The first springs 10 exert forces in a direction which is perpendicular to the planes of the first actuating wall 8 and the first end plate 4, and the second springs 15 exert forces in a direction which is perpendicular to the planes of the second actuating wall 14 and the second end plate 5.
[0040] The cams 9 are mounted in a system 1 according to the invention, so that their second ends 17 comprising the elongated segment bear against the first actuating wall 8.
[0041] The operating principle of such a system is that a computer 13 to which the actuator 12 is connected will send to this actuator 12 instructions in the form of signals, to move the connecting rod 11 in one direction or the other. The connecting rod 11 is then translated along its longitudinal axis in a given direction and with the desired amplitude, thus causing the cams 9 to pivot. The rotation of the connecting rod 18 of each cam 9 causes the second end 17 of said cam, which is fixed to said rod 18 due to the presence of the rotation axis secured to the first wall 19 of the frame 6, the pivoting of this second end 17 bringing the first actuating wall 8 closer to or further away from the first end plate 4 of the electric battery 2. The first springs 10 will then either compress or relax, to apply a more or less significant pressure on said first end plate 4.The second assembly 40 will then react in the same way as the first component 7, that is to say that if the first springs 10 compress under the effect of the pivoting of the cams 9, the second springs 15 will also compress and if they relax, said second springs 15 will also relax. The second assembly 40 plays a relay role to balance the pressure exerted on the battery 2 by the first assembly 7.
[0042] Referring to Figures 1 to 6, when the cells of the battery 2 are not aged, a method of using a system 1 according to the invention during a complete cycle comprising a charging phase followed by a discharging phase of said battery 2, comprises the following steps: -Referring to figures 1 and 2a, a starting stage for which the cells are at dimension xl and system 1 exerts a force Fl, - Referring to Figures 2a, 2b and 3, a charging step of battery 2 for which the force exerted by system 1 increases to a value F2 which is greater than Fl, because the cells of battery 2 have expanded during the charging phase and are now at a dimension x2 which is greater than xl. This force F2 is the force re- resultant exerted by system 1 at the end of the load, -Referring to figures 2a and 4, a step of starting a discharge of the electric battery 2 comprising a step of prior activation of the system 1 controlled by the computer 13 for which the connecting rod 11 is translated upwards causing a rotation of the cams 9 in a direction which will bring the first actuating wall 8 closer to the first end plate 4. During this step of prior activation, the system 1 then instantaneously exerts a resultant force F3 on the battery 2, which is greater than the force F2, -Referring to figures 2a, 2b and 5 an end of discharge step for which the cells have regained a dimension xl, and the system applies a resulting force F4 on the battery 2 which is less than the force F3, this force F4 applied at the end of discharge being due to the cells which have lost volume during this discharge phase, -Referring to figures 2a and 6, an activation step of the system 1 controlled by the computer 13 for which the connecting rod 11 is translated downwards causing a rotation of the cams 9 in a direction which will move the first actuating wall 8 away from the first end plate 4. The system 1 then instantly exerts a force Fl on the battery 2, which is less than the force F4. We are then in the ready position for charging
[0043] Referring to Figures 7 to 12, when the cells of the battery 2 are aged, they tend to increase their volume over time, this phenomenon being irreversible. The use of a system 1 according to the invention during a complete cycle of a charging phase followed by a discharging phase of said aged battery follows the following steps: -Referring to Figures 7a, 7b and 8, a starting stage for which the cells are at a dimension x3 which is greater than the initial dimension xl when the cells are not aged, and system 1 exerts a resultant force Fl, -Referring to Figures 7a, 7b and 9, a charging step of battery 2 for which the force exerted by system 1 increases to a value F2 which is greater than Fl, because the aged cells of battery 2 have expanded during the charging phase and are now at a dimension x4 which is greater than x3. This force F2 is the force exerted by system 1 at the end of charging, -Referring to figures 7a and 10, a step of starting a discharge of the electric battery 2 comprising a step of prior activation of the system 1 controlled by the computer 13 for which the connecting rod 11 is translated upwards causing a rotation of the cams 9 in a direction which will bring the first actuating wall 8 closer to the first end plate 4. During this step of prior activation, the system 1 then instantly exerts a force F3 on the battery 2, which is greater than the force F2, -Referring to figures 7a, 7b and 11, an end of discharge stage for which the cells have regained a dimension x3 at the end of discharge, and the system applies a force F4 on battery 2 which is lower than the force F3, this force F4 applied at the end of discharge being due to the cells which have lost volume during this discharge phase, -Referring to figures 7a and 12, a step of activation of the system 1 controlled by the computer 13 for which the connecting rod 11 is translated downwards causing a rotation of the cams 9 in a direction which will move the first actuating wall 8 away from the first end plate 4. The system 1 then instantly exerts a force Fl on the battery 2, which is less than the force F4.
[0044] The different steps of the pressure management process when the battery cells have been aged are identical to those of the pressure management process when they have not been aged, only their initial dimension x3 is greater than the initial dimension xl of the cells which have not been aged, due to an initial increase in the volume of these aged cells.
[0045] It should be noted that the step of charging the battery 2 is not carried out only when the state of charge thereof is zero, but from any state of charge. Similarly, the discharging step is not systematically carried out until the state of charge of the battery has a value of zero. It can be interrupted at any time while the state of charge of the battery is not zero.
Claims
Claims
1. System (1) for applying variable pressure to an electric battery (2) comprising at least one electrochemical cell, inserted between a first end plate (4) and a second end plate (5) parallel to each other, characterized in that it comprises a first assembly (7) comprising a first actuating wall (8) extending parallel to the two end plates (4, 5) and located opposite the first end plate (4), and in that said first assembly (7) comprises at least one first spring (10) inserted between the first actuating wall (8) and the first end plate (4), said first actuating wall (8) being able to move towards or away from the first end plate (4) to exert pressure on said first plate (4), under the effect of the movement of a link (11) extending parallel to the first wall (8) actuated and driven by an actuator (12),said connecting rod (11) being connected to said first actuating wall (8) by at least one cam (9) of which a first end (16) is mounted in rotation on the connecting rod (11), and of which a second end (17) is mounted in rotation around an axis of rotation secured to a fixed wall (19) parallel to the first actuating wall (8), said second end (17) bearing against the first actuating wall (8).,
2. Pressure application system according to claim 1 characterized in that the connecting rod (11) is an elongated rod, and in that the actuator (12) moves said connecting rod (11) in translation along a longitudinal axis of this connecting rod (11).
3. Pressure application system according to claim 2, characterized in that each cam (9) comprises a rod (18) connecting the first end (16) to the second end (17), and in that said second end (17) comprises an elongated segment, which is placed around the axis of rotation.
4. Pressure application system according to any one of claims 1 to 3, characterized in that it comprises a computer (13) intended to control the actuator (12) to move the connecting rod (11) in the desired direction and with the desired amplitude, so as to place the first actuating wall (8) at a given distance from the first end plate (4) in order to compress each first spring (10) for exerting the desired pressure on said first end plate (4).
5. Pressure application system according to any one of claims 1 to 4, characterized in that it comprises a second assembly (40) comprising a second actuating wall (14) extending parallel to the two end plates (4, 5) and located opposite the second end plate (5), said second assembly (40) comprising at least one second spring (15) inserted between the second actuating wall (14) and the second end plate (5), the direction of the forces exerted by said at least one second spring (15) being parallel to the direction of the forces exerted by said at least one first spring (10), said second actuating wall (14) bearing against a fixed wall (20) which is parallel to said second actuating wall (14).
6. Pressure application system according to claim 5, characterized in that it comprises twelve first springs (10) inserted between the first actuating wall (8) and the first end plate (4) and twelve second springs (15) inserted between the second actuating wall (14) and the second end plate (5).
7. A pressure application system according to any one of claims 5 or 6, characterized in that the first springs (10) are aligned along an axis which is parallel to the end plates (4, 5) and the second springs (15) are also aligned along an axis which is parallel to said end plates (4, 5).
8. Pressure application system according to any one of claims 5 to 7, characterized in that each first spring (10) and each second spring (15) are constituted by Belleville washers.
9. Pressure application system according to any one of claims 5 to 8, characterized in that it comprises a fixed frame (6) enclosing the electric battery (2), the first actuating wall (8), the second actuating wall (14), said at least one first spring (10), said at least one second spring (15), and in that the second actuating wall (14) is in contact with a second flat wall (20) of the frame (6) and said at least one axis of rotation around which the second end (17) of said at least one cam (9) is mounted is secured to a first flat wall (19) of the frame (6) which is parallel to said second flat wall (20), the connecting rod (11) being located behind said first flat wall (19) of the frame (6) while being placed outside said frame (6).
10. Method of using a system according to any one of claims 1 to 9 during a cycle comprising a charging phase then a discharging phase of a Li-ion electric battery, characterized in that it comprises the following steps: - a starting step for which the cells are at dimension xl and the system (1) exerts a force Fl, - a step of charging the electric battery (2) for which the force exerted by the system (1) increases to a value F2 which is greater than Fl, because the cells of the battery (2) have expanded during the charging phase and are now at a dimension x2 which is greater than xl, - a step of starting a discharge of the battery 2 comprising a step of prior activation of the system (1) controlled by the computer (13) for which the connecting rod (11) is translated in a direction causing a rotation of the cams (9) in a first direction which will bring the first actuating wall (8) closer to the first end plate (4), said system (1) then instantly exerting a force F3 on the battery (2), which is greater than the force F2, - a step of ending the discharge of the battery (2) for which the system (1) applies a force F4 to the battery (2) which is less than the force F3,this force F4 applied at the end of discharge being due to the cells which have lost volume during this discharge phase, - a step of activation of the system (1) controlled by the computer (13) for which the connecting rod (11) is translated in an opposite direction causing a rotation of the cams (9) in a second direction which will move the first actuating wall (8) away from the first end plate (4), said system (1) then instantly exerting a force Fl on the battery (2), which is less than the force F4, to make the cells return to their pre-charge pre-stressed state.,