DEVICE FOR MEASURING DIMENSIONAL VARIATIONS IN ELECTROCHEMICAL CELLS OF BATTERIES

Abstract

A device for measuring the dimensional variations of electrochemical battery cells during charge and discharge cycles, comprising, along a main axis (A) between a lower plate (2) and an upper plate (4) of a rigidly connected press, a stack including a fixed plate (14) and a movable plate (12) for clamping a cell together by applying an axial force, a sensor for this axial force (26), a sensor for the axial displacement of the movable plate (12), and a hydraulic cylinder (16) comprising, on one side of a piston, a first chamber delivering a first force towards the cell, and on the other side, a second chamber, equipped with a reservoir with a gas pressure accumulator (66), delivering a second pressure control force which is opposed to the first force to ultimately give the axial force applied by the cylinder (16). Figure 1

Description

Title of the invention: DEVICE FOR MEASURING DIMENSIONAL VARIATIONS IN ELECTROCHEMICAL CELLS OF BATTERIES

[0001] The present invention relates to a device for measuring dimensional variations of electrochemical battery cells during charge and discharge cycles, as well as a method for implementing such a device.

[0002] The electrochemical cells of electrical energy storage batteries exhibit volume variations during charge and discharge cycles. In particular, a cycle, reversible or irreversible, of swelling of the cell materials is observed during charging, which increases the external dimensions, and a contraction during discharge with a return to the original state.

[0003] These dimensional variations depend on numerous criteria such as the type of materials used, the cell temperature, and the external force applied to the surfaces. Furthermore, the cells can have different external shapes, in particular cylindrical, prismatic, or variously shaped cells without external protection, called pouch cells. The cells may also be subject to various positioning and fixing constraints within the controlled enclosure of a battery grouping these cells.

[0004] Unforeseen dimensional variations in cells can cause problems of high stress on the internal materials and the cell casing, and damage leading to malfunctions or even accidents such as fires. Accurate knowledge of these variations is important for optimizing battery design, particularly for traction batteries in electric or hybrid vehicles, which require high energy density for a given mass and volume to achieve maximum vehicle range and limited weight, while maintaining a high level of safety.

[0005] A known type of device for measuring the dimensional variations of electrochemical cells, described in particular by US-A1-20230296676, comprises a press including a workspace between a base plate and an upper plate rigidly connected by columns. The base plate receives a stack comprising successively a lower force sensor measuring the vertical force applied to the stack, a cell support plate, the cell, and an upper support plate for this cell. A displacement sensor measures the vertical sliding of the upper support plate.

[0006] The upper plate of the press has vertical screws for applying pressure to a compression plate which, via pressure springs, acts on the upper support plate, compressing the cell. The pressure screws allow the position of the compression plate to be defined, which then determines the available height for the compressed springs pressing on the support plate against the cell.

[0007] A hydraulic cylinder coming above the press can be used to apply a force on the compression plate, compressing the springs below in order to allow effortless adjustment of the tightening of the pressure screws.

[0008] In all cases, a fixed positioning of the compression plate is obtained, which then gives variations in the length of the pressure springs as a function of the swelling of the cell volume during its charging or its retraction during its discharging.

[0009] We can then predict from the outset a minimum level of pressure applied by the springs on an unloaded cell, and study its swelling during electrical charging by measuring both the rise of the upper support plate which compresses the springs, and the increase in the vertical force linked to this compression of the springs, given by the lower force sensor.

[0010] Alternatively, a higher level of pressure applied by the springs on a loaded cell can be provided at the start, and its contraction can be studied during unloading by measuring both the descent of the upper support plate which relaxes the springs, and the decrease in the vertical force.

[0011] In all cases, it is not possible to carry out certain types of measurements during the charging and discharging cycles, such as a measurement of the dimensional variations of the cell under a predefined variable force, or a measurement of the force variations for a predefined distance between the support plate and the upper support plate.

[0012] The present invention is specifically intended to avoid these problems of the prior art.

[0013] To this end, it proposes a device for measuring the dimensional variations of electrochemical battery cells during charge and discharge cycles, comprising, along a main axis between a lower plate and an upper plate of a press rigidly connected, a stack comprising a fixed plate and a movable plate for clamping a cell together by applying an axial force, a sensor for this axial force, and a sensor for the axial displacement of the movable plate, this device being remarkable in that it comprises a hydraulic cylinder comprising, on one side of a piston, a first chamber delivering a first force towards the cell, and on the other side, a second chamber, equipped with a reservoir with a gas pressure accumulator, delivering a second pressure control force which is opposed to the first force to ultimately give the axial force applied by the cylinder.

[0014] One advantage of this device is that the gas pressure accumulator makes it possible in particular to stabilize with high precision the hydraulic pressure in the force control chamber to carry out inflation measurements of the cell subjected to a constant force, or to finely regulate this force delivered by the hydraulic pressure linked to a gas pressure that is easily and precisely controllable.

[0015] In particular, during load cycles, the geometric variations of the cell can be measured by applying a force maintained at a constant value which remains precise, or the force applied to the cell disposed between the two plates which are maintained with a constant gap can be measured.

[0016] In all cases the simultaneous measurement of the displacement of the moving plate, of the axial force applied to it, and the precise modulation of the pressure applied by the cylinder allows a large number of types of measurements on the cell allowing to optimize its design, and that of the secure battery enclosure including the cell fixings, in particular to produce a traction battery for an automobile vehicle.

[0017] The measuring device according to the invention may further comprise one or more of the following characteristics, which may be combined with each other.

[0018] Advantageously, the force application chamber includes a second reservoir with a gas pressure accumulator for controlling the volume of fluid in this chamber.

[0019] Advantageously, the tanks with accumulators each have an adjustable control of their gas volume.

[0020] Advantageously, the reservoirs with accumulators each include an elastomer membrane separating the gas from the hydraulic cylinder fluid.

[0021] Advantageously, the measuring device includes a valve for adjusting the fluid volumes in each of the cylinder chambers.

[0022] Advantageously, the force sensor is arranged above the plates and the hydraulic cylinder below the lower plate.

[0023] The invention also relates to a method for controlling a measuring device comprising any of the preceding characteristics, remarkable in that for a test with constant axial force on the cell it performs in real time a comparison of the pressure in the force application chamber with a setpoint pressure, in order to adjust it by modifying the volume of gas in the first tank with accumulator.

[0024] Advantageously, the method performs a zero axial force test on the cell by balancing the first force given by the first chamber and the second force given by the second chamber.

[0025] Advantageously, the first chamber comprising a fluid volume control reservoir with a gas pressure accumulator, for a test under a constant axial force, when this cell is inflated, giving an increase in the force applied to it, measured by the force sensor, the quantity of gas in this volume control reservoir is decreased to lower the fluid volume of the first chamber, and when the cell is contracted, this quantity of gas is increased.

[0026] Advantageously, the method performs measurements on electrochemical cells of a motor vehicle traction battery.

[0027] The invention will be better understood and other features and advantages will become more apparent upon reading the following description given by way of example, with reference to the accompanying drawings in which:

[0028] [Fig-1] presents a measuring device according to the invention;

[0029] [Fig.2] presents this device in axial section;

[0030] [Fig.3] presents the force sensor of this device;

[0031] [Fig.4] presents the lower plate displacement sensor of this device;

[0032] [Fig.5] shows a view from below of the cylinder of this device;

[0033] [Fig.6] is a diagram of the operation of the cylinder of this device; and

[0034] [Fig.7] presents, as an alternative, a support for a cylindrical cell replacing the trays.

[0035] Throughout the document the upper or top direction is relative to the figures showing the press of the measuring device, which is arranged vertically in this example.

[0036] Figures 1 and 2 show a measuring device comprising a vertical press including, arranged horizontally, a fixed base plate 2 and an upper plate 4, and including two vertical tubes 6 passing through the upper plate, having their lower ends fixed to the base plate, and their upper ends connected to each other by a horizontal tube 8 above this upper plate. Two lateral jacks 10 connect the base plate 2 to the upper plate 4 to effortlessly lift and adjust the height of this upper plate, which is then clamped to form a rigid frame comprising these two parallel plates.

[0037] The measuring device comprises two parallel platforms including an upper support platform 14 suspended under the upper plate 4 by an axial force sensor 26 protected in a hood, and a lower support platform 12 sliding vertically, connected by a cylinder 16 arranged along the vertical axis A to the base plate 2.

[0038] Figure 3 shows the axial force sensor 26 having a machined shape in a metal plate of constant thickness, comprising a horizontal upper arm 40 and a lower horizontal arm 42 which are connected to each other at their opposite ends by passing through a central part 44 so as to form an overall "S" shape. The central part 44 has in its middle a hole 46 comprising two circular parts which meet.

[0039] Each horizontal arm 40, 42 has an axial bore 48 receiving a vertical fixing rod 28, 30. The upper fixing rod 28 is fixed to the upper plate 4, and the lower rod 30 is fitted into a sleeve 34 formed on the top of the upper plate 14, with a horizontal through pin 32 allowing quick disassembly of this connection.

[0040] A strain gauge fixed on the central part 44 of the force sensor 26 measures the stresses applied in the metal during an axial compression between the horizontal arms 40, 42 transmitted by the fixing rods 28, 30, representing the axial compression force applied on the cell disposed between the plates 12, 14.

[0041] The cylinder 16 comprises a body 50 rigidly fixed under the base plate 2, containing a piston 52 fixed to a cylinder rod 54 the upper end of which is fitted into a sleeve 34 formed under the lower plate 12 with a retention by a horizontal pin 32. In this way the two plates 12, 14 can be changed quickly by removing the horizontal pins 32 freeing their sleeves 34 from the cylinder rod 54 or from the lower rod 30 of the axial force sensor 26.

[0042] Each plate 12, 14 has on the surface opposite the other shapes allowing to receive an electrochemical cell, for example cylindrical arranged vertically or horizontally, or any other prismatic shape, so as to apply with the cylinder 16 a vertical axial compressive stress on this cell arranged between them.

[0043] Alternatively, a vertical stack of cells can be arranged between the plates 12, 14, allowing the dimensional variations of this stack to be studied under constraint, which can then form a battery module.

[0044] Fig. 4 shows a vertically arranged displacement sensor 70, comprising a housing 36 fixed to the side of the cylinder rod 18 by a collar surrounding it, and a sliding axis 38 having an upper tip bearing under the base plate 2, for measuring the vertical displacements of the lower plate 12 moving the housing with the cylinder rod relative to this base plate.

[0045] We then obtain a measurement of the variation in distance between the two plates 12, 14, representing along the vertical axis A the variations in the dimension of the cell which is squeezed between these plates.

[0046] The press is arranged in a climatic chamber allowing adjustment of the ambient operating conditions of the cell, in particular the temperature and the composition of the internal gas. The press may include other sensors, in particular temperature sensors of the cell. By applying cycles of charging and discharging electrical energy to the cell, the relationships between axial force, the axial distance between the two plates 12, 14, and other parameters such as the temperature of this cell are studied under different conditions.

[0047] Figures 5 and 6 show the cylinder 16 comprising the lower end of its rod 54 linked to a piston 52 separating a first lower chamber delivering a force to the cell 56, connected to a reservoir controlling its volume 62, from a second upper chamber controlling the force 58 connected to a reservoir controlling its pressure 66. A system of solenoid valves 60 allows each chamber of the cylinder 56, 58 to be supplied with fluid.

[0048] The volume control tank 62 and the pressure control tank 66 each include a gas pressure accumulator comprising a supply 64 of this gas with a controlled pressure, which is separated from the fluid by an elastomer membrane.

[0049] An electronic control device monitors all the operating parameters of the measuring device, including in particular the measurement of the axial force applied to the force sensor 26, the measurement of the displacement of the lower plate 12 given by the displacement sensor 70, the volume of fluid in each chamber of the cylinder 56, 58, and the pressure in these chambers which is related to the gas pressure in their reservoir accumulator 62, 66.

[0050] The control device also monitors the operating parameters of the climate chamber during charge and discharge cycles of the electrochemical cells. The climate chamber also allows for the control of the gases present inside, in particular to prevent fires caused by gases emitted by the deteriorating cell, or internal short circuits.

[0051] During a cell operating cycle in a test under a constant axial force, when the cell inflates, resulting in an increase in the force applied to it (measured by the force sensor 26), the gas volume in the accumulator of the volume control reservoir 62 is decreased to reduce the fluid volume in the lower chamber delivering a force to the cell 56, in order to obtain the set axial force. Conversely, when the cell contracts, the gas volume is increased to add fluid to the lower chamber 56. This avoids measurement errors that could be caused by various parameters such as variations in the viscosity of the fluid in the hydraulic circuit.

[0052] The pressure control reservoir 66 allows the resulting axial force developed on the rod of the cylinder 54 to be stabilized in real time by adjusting the volume of gas in its accumulator, thus providing a control pressure for the second upper chamber 58 delivering a control force which opposes the force delivered towards the cell by the first lower chamber 56, in order to obtain in total the axial force required on this cylinder rod which is directly applied to the cell.

[0053] In particular, for a test with constant axial force on the cell, a real-time comparison of the pressure in the lower chamber 56 with a setpoint pressure is made, in order to adjust it by modifying the volume of gas in the accumulator of the pressure control tank 66. In particular, a zero force can be applied to the cell, giving a free expansion mode of the cell.

[0054] For a test with a variable axial force cycle defined on the cell, the gas volume in the accumulator of the pressure control tank 66 is modified in real time to obtain this variable setpoint force. Tests can also be carried out with a fixed gap between the plates 12, 14, or with a variable gap according to a predefined cycle.

[0055] Figure 7 shows a support for a cylindrical cell 80 replacing the plates 12, 14, comprising a cradle 82 forming a half-cylinder fitted to the shape of the cell, and on the back the sleeve 34 which fits onto the lower rod 30 or the cylinder rod 54. By removing the transverse pins 32 the plates 12, 14 are removed to be replaced by two supports for cylindrical cells 80 in order to distribute the pressure over the entire surface of these cells.

[0056] Alternatively, other shapes of cradles 82 can be provided which fit onto particular cell contours.

[0057] In general, the measuring device according to the invention allows any type of measurement including axial force setpoints on the cell, or distance between the two plates 12, 14, which are precisely controlled in real time during the charging and discharging cycles.

[0058] The measuring device makes it possible to study all types of cells, including in particular new energy storage materials such as silicon or lithium metal with significant volume variations, in order to optimize the envelope of these cells and their installation in the battery in order to meet safety requirements, and to obtain high energy density and optimal aging.

Claims

Demands

1. Device for measuring the dimensional variations of electrochemical battery cells during charge and discharge cycles, comprising along a main axis (A) between a lower plate (2) and an upper plate (4) of a press rigidly connected, a stack comprising a fixed plate (14) and a movable plate (12) for clamping a cell together by applying an axial force, a sensor of this axial force (26), and an axial displacement sensor (70) of the movable plate (12), characterized in that it comprises a hydraulic cylinder (16) comprising on one side of a piston (52) a first chamber delivering a first force towards the cell (56), and on the other side a second chamber (58), equipped with a reservoir with a gas pressure accumulator (66), delivering a second pressure control force which is opposed to the first force to ultimately give the axial force applied by the cylinder (16).

2. Measuring device according to claim 1, characterized in that the first chamber (56) comprises a reservoir with gas pressure accumulator (62) for controlling the volume of fluid in this first chamber (56).

3. Measuring device according to claim 2, characterized in that the tanks with accumulators (62, 66) each have an adjustable control of their gas volume.

4. Measuring device according to claim 2 or 3, characterized in that the reservoirs with accumulators (62, 66) each have an elastomer membrane separating the gas from the fluid of the hydraulic cylinder (16).

5. A measuring device according to any one of the preceding claims, characterized in that it comprises a valve (60) for adjusting the fluid volumes in each of the chambers of the cylinder (56, 58).

6. Measuring device according to any one of the preceding claims, characterized in that the force sensor (26) is disposed above the plates (12, 14) and the hydraulic cylinder (16) below the lower plate (2).

7. A method for testing a measuring device according to any one of the preceding claims, characterized in that, for a test with constant axial force on the cell, it performs in real time a comparison of the pressure in the first chamber (56) with a set pressure, to adjust it by changing the volume of gas in the pressure control tank (66) of the second chamber (58).

8. A control method according to claim 7, characterized in that it performs a zero axial force test on the cell by balancing the first force given by the first chamber (56) and the second force given by the second chamber (58).

9. A method for controlling a measuring device according to any one of claims 1 to 6, the first chamber (56) comprising a fluid volume control reservoir with a gas pressure accumulator (62), characterized in that, for a test under a constant axial force, during an inflation of this cell giving an increase in the force applied to it, measured by the force sensor (26), the quantity of gas in this volume control reservoir (62) is decreased to lower the fluid volume of the first chamber (56), and during a contraction of the cell this quantity of gas is increased.

10. A control method according to any one of claims 7 to 9, characterized in that it performs measurements on electrochemical cells of a motor vehicle traction battery.

Images