Device and method for detecting deformation of battery cell packaging

Abstract

Device and method for detecting deformation of a battery cell package. Method for detecting deformation of a package containing a battery cell (3), using a detection device comprising a Wheatstone bridge (6), the method comprising: measuring a current temperature of the package (2); accessing the lookup table (14) of the device; setting a value of the variable resistance (R3) of the device to a value associated with the current temperature in the lookup table (14); measuring an output voltage (Vout) of the Wheatstone bridge (6) of the device; and detecting deformation of the package (2) when the output voltage (Vout) is different from a reference voltage threshold (Vref). Figure for abstract: Fig. 1

Description

Title of the invention: Device and method for detecting deformation of a battery cell packaging Technical field

[0001] The present invention relates to electrical energy storage units, such as a battery cell, in particular a lithium-ion battery, and more particularly to the management of such cells, in particular the detection of deformation of a packaging of such a cell. STATE OF THE ART

[0002] Currently, small batteries, also called "Smart Cell" in English, are used, a generic term which describes a battery cell, for example a lithium-ion or Li-ion battery, equipped with a battery management system, noted "Battery Management System, or BMS" in English dedicated to self-measurement, self-diagnosis, self-balancing of the battery. An important point of self-diagnosis is the monitoring of the safety status of the cell. In addition, small batteries generally comprise one or more cells housed within an airtight package.

[0003] For example, the study of the deformation of the packaging of a Li-ion cell is known by exploiting the signal of a strain gauge applied to its surface. The deformation may, in fact, be the sign of an abnormal accumulation of gas which may cause the packaging to swell, caused for example by an overcharge, an excessive discharge or the start of thermal runaway which may cause the packaging to expand. Under nominal operating conditions of the cell, the deformation may be linked to the state of charge of the cell (denoted SoC) or to the state of health of the cell (denoted SoH).

[0004] Strain gauges are sensors that are extremely sensitive to temperature, meaning that their signal changes as much due to deformation as to temperature. The use of so-called self-compensated gauges, which are supposed to drift in temperature so as to compensate for the thermal expansion of the material to which they are applied, is not sufficient to avoid the influence of temperature on the usable signal, because a battery cell is comparable to a rather heterogeneous object, composed of different metals, electrolyte and a packaging that may be metallic or made of a thin layer of aluminum covered with polymer on both sides. In addition, the self-compensation of the gauges is only valid over a restricted temperature range, generally between 10°C and 50°C. However, for battery cells, the temperature may vary from -20°C to 60°C, and it may be interesting to know the deformations of the packaging at the operating temperature limits of a battery.

[0005] Furthermore, a conventional use of two strain gauges on two opposite faces of an object undergoing opposite deformations is also not possible for a cell housed within a hermetic package, because access to the interior of the cell is not possible.

[0006] We can also cite the use of two gauges, including a reference gauge. For example, gauges called "Dummy gauges" in English, that is to say fictitious gauges. Dummy gauges use a first active strain gauge and a second gauge identical to the first, installed on an undeformed sample of the same material as that of the element whose deformation we wish to measure. But fictitious gauges are bulky systems.

[0007] To improve the measurement of a strain gauge, it is possible to use measurement systems using high-resolution digital converters (greater than or equal to 24 bits). But these techniques are intended for use in the laboratory, in particular because most of these converters are powered by 5 Volts, from a 220 V voltage source, called high voltage. These converters are not suitable for being powered by a battery, in particular a small battery, providing a voltage of 2.5 Volts, called low voltage.

[0008] We can also cite systems using a calibration of the signal of a strain gauge, for example, the American patent application US3130578, which discloses a system comprising a Wheatstone bridge for measuring the signal of a strain gauge equipped with a control circuit controlled by switches, to short-circuit a resistance of the Wheatstone bridge. But this system uses control circuits and switches which are complex to implement, and which are also consumers of electrical energy.

[0009] An object of the present invention is therefore to provide means for improving the detection of deformation of a packaging of a battery cell, and more particularly by overcoming the influence of temperature on the detection devices.

[0010] Other objects, features and advantages of the present invention will become apparent from the following description and accompanying drawings. It is understood that other advantages may be incorporated. SUMMARY

[0011] A device for detecting deformation of a battery cell packaging is proposed, comprising: - a measuring circuit comprising a Wheatstone bridge itself comprising a strain gauge having a resistance varying as a function of a de- packaging formation, and - an electronic control unit configured to: • measure an output voltage of the Wheatstone bridge, and for • detect packaging deformation when the output voltage is different from a reference voltage threshold.

[0012] The Wheatstone bridge comprises a variable resistor whose value is controlled by the electronic control unit, and the device comprises: - a temperature sensor configured to measure a temperature of the packaging; and - a memory in which is stored a correspondence table comprising values ​​of the variable resistance associated respectively with temperatures for which the battery cell is in a normal operating state.

[0013] The electronic control unit is further configured to: - determine a current temperature from the temperature sensor, and to - set the value of the variable resistor to the value associated with the current temperature in the correspondence table.

[0014] Thus, a device is provided for detecting deformation of a battery cell packaging while avoiding the influence of temperature on the detection devices. Such a device is particularly suitable for being installed, with the battery, within mobile equipment, for example portable.

[0015] According to another aspect, a method is proposed for detecting a deformation of a package containing a battery cell, using a detection device as defined above.

[0016] The method comprises: - a measurement of a current temperature of the packaging; - access to the device correspondence table; - a placement of a value of the variable resistance of the device to a value associated with the current temperature in the correspondence table; - a measurement of an output voltage of the Wheatstone bridge of the device; and - detection of packaging deformation when the output voltage is different from a reference voltage threshold. BRIEF DESCRIPTION OF THE FIGURES

[0017] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:

[0018] [Fig.l] [Fig.l] schematically represents an embodiment of a device for detecting a deformation of a packaging of a battery cell;

[0019] [Fig.2] [Fig.2] schematically represents another embodiment of the detection device illustrated in [Fig.l].

[0020] The drawings are given as examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of practical applications. DETAILED DESCRIPTION

[0021] Before beginning a detailed review of embodiments and implementations of the invention, optional features which may possibly be used in combination or alternatively are set out below.

[0022] According to one example, the electronic control unit is configured to measure a deformation of the package from the measured output voltage.

[0023] According to one example, the Wheatstone bridge is electrically coupled to the battery cell and an excitation voltage of the Wheatstone bridge is provided by the battery cell. A device is provided which is particularly suitable for being embedded, with the battery cell, within electrical energy consuming equipment, for example portable equipment.

[0024] According to an example, wherein the Wheatstone bridge is electrically coupled to the electronic control unit and an excitation voltage of the Wheatstone bridge is provided by the electronic control unit.

[0025] According to one example, the Wheatstone bridge comprises first and second resistors electrically coupled together in series, the variable resistor and the strain gauge being electrically coupled together in series and electrically coupled in parallel with the first and second resistors.

[0026] According to one example, the first and second resistors are made on the same semiconductor substrate and the variable resistor is made on the same semiconductor substrate. The effect of temperature on the equipment of the detection device is further limited.

[0027] According to one example, the variable resistor has a first terminal electrically coupled to a terminal of the strain gauge via a first additional resistor, and a second terminal electrically coupled to the terminal of the strain gauge via a second additional resistor, the value of the second additional resistor being strictly less than that of the first additional resistor. Such a device is suitable for strain gauges having a resistance whose nominal value is low, for example 120 Ohms, 350 Ohms or 1000 Ohms.

[0028] According to one example, the temperatures of the correspondence table are between -20°C and +60°C.

[0029] According to one example, the temperatures in the correspondence table are 5°C apart in pairs.

[0030] According to one example, the battery is of the lithium-ion type.

[0031] According to one example, the method comprises measuring a deformation of the package from the measured output voltage.

[0032] According to one example, the method comprises, before accessing the correspondence table: - a creation of the correspondence table comprising, for each temperature of the correspondence table: • placement of the packaging at a temperature corresponding to the temperature in the correspondence table; • a measurement of the output voltage of the Wheatstone bridge; • a placement of the value of the variable resistor to a value associated with the temperature so that the output voltage is equal to a reference voltage threshold corresponding to a normal operating state of the battery cell; and • a record, in the correspondence table, of the value associated with the temperature; and - a recording, in the device's memory, of the correspondence table.

[0033] It is specified that in the context of the present invention, the expression "A coupled to B" or "A electrically coupled to B" is synonymous with "A is in electrical connection with B" and does not necessarily mean that there is no member between A and B. Thus these expressions are understood to mean an electrical connection between two elements, this connection being able or not to be direct, this means that it is possible that between a first device A and a second device B which are electrically connected, a current flows in A, in B, and on the path connecting A to B, this path being able or not to include other electrical equipment.

[0034] Conversely, in the context of the present invention, the term "electrically directly coupled" means a direct electrical connection between two elements. This means that between a first device A and a second device B which are electrically directly coupled no other equipment is present, other than one or more electrical connections.

[0035] In [Fig.l], a device 1 for detecting a deformation of a packaging 2 of a cell 3 of battery 30 is shown. In other words, the battery 30 comprises a packaging 2 within which one or more cells 3 are housed. The packaging 2 can be cylindrical, for example prismatic, cylindrical with a circular cross-section, or parallelepiped. A cylinder, or cylindrical shape, is a solid delimited by an external surface, called cylindrical, and by two planes. The cylindrical surface is described by a straight line of constant direction, called the generating line, moving along a closed curve, called the directrix curve. When a plane is not perpendicular to the generating line, the cylinder is truncated. When a plane is perpendicular to the generating line, the cylinder is right. When the cross-section of the cylinder is circular, the cylinder is said to be circular. A right circular cylinder is called a cylinder of revolution. When the directrix curve is a polygon and the planes are parallel, the cylinder is a prism. A parallelepiped is a solid delimited by six faces which are parallelograms.In the case of battery cells, the parallelepiped is typically a prism whose directrix curve is a rectangle. Packaging 2 can be flexible, such as a prismatic or parallelepiped-shaped bag, or semi-rigid, such as a circular, prismatic, or parallelepiped cylindrical case. Flexible packaging means packaging that can deform under its own weight. Semi-rigid packaging means packaging that does not deform under its own weight and can deform with a radius of curvature without breaking. Semi-rigid packaging is also said to have a Young's modulus strictly greater than that of flexible packaging. Semi-rigid packaging is less flexible than flexible packaging. In the case of semi-rigid packaging, typically produced by stamping thin metal sheets, it remains sufficiently flexible to allow deformation.For example, the battery 30 is of the lithium-ion type. A lithium-ion battery comprises one or more cells 3, called lithium-ion cells. Each cell 3 comprises two electrodes separated by an electrolyte configured to generate charge carriers, in particular lithium ions.

[0036] The device 1 comprises a measuring circuit 4 and an electronic control unit 5. More particularly, the measuring circuit 4 comprises a Wheatstone bridge 6. The Wheatstone bridge 6 comprises first and second resistors RI, R2, and a strain gauge 7. In particular, the strain gauge 7 is placed in contact with the packaging 2 of the battery 30. Furthermore, the Wheatstone bridge 6 comprises first and second input terminals EPI, EP2 and first and second output terminals SP1, SP2. The first resistor RI has its terminals electrically coupled, and preferably directly, respectively to the first input terminal EPI and to the first output terminal SP1. The second resistor R2 has its terminals electrically coupled, and preferably directly, respectively to the first output terminal SP1 and to the second input terminal EP2. More particularly, the first and second resistors RI, R2 each have a constant resistance value. For example, the first and second resistors RI, R2 have equal resistance values.

[0037] The strain gauge 7 has a resistance Rx varying as a function of a deformation of the package 2. The value of the resistance Rx of the strain gauge 7 corresponds to the value observed when the strain gauge 7 is subjected to a deformation. The resistance Rx of the strain gauge 7 has its terminals electrically coupled, preferably directly, respectively to the first input terminal EPI and to the second output terminal SP2. The strain gauge 7 emits a signal which changes as a function of a deformation of the package 2. In particular, the value of the resistance Rx varies as a function of the deformation of the package 2. Thus, the Wheatstone bridge 6 makes it possible to measure the deformation of the package 2, by measuring the signal from the strain gauge 7.

[0038] The measuring circuit 4 and the electronic control unit 5 can be printed on a printed circuit board 100, called “Printed Circuit Board” in English.

[0039] The first and second input terminals EPI, EP2 are configured to receive an excitation voltage Vexe. The excitation voltage Vexe can be provided by the card 100. Thus, an excitation voltage Vexe, for example 5V, can be provided. Preferably, the card 100 is electrically coupled to the battery cell 3 and the excitation voltage Vexe is provided by the battery cell 30. Thus, the card 100 and the battery 30 can be embedded within the same equipment. The card 100 and battery 30 assembly is therefore compact. For example, the input terminals EPI, EP2 are respectively coupled to output terminals 101, 102 of the battery 30, by connections 103, 104. The excitation voltage Vexe of the Wheatstone bridge 6 can be provided by the battery cell 30.

[0040] Preferably, the voltage which supplies the electronic elements of the device 1, namely the temperature sensor 10, the electronic control unit 5 and the memory 11, comes from the cell 3 itself. The lowest voltage of a cell 3 is approximately 2.5 V, for example 2.2 V, which corresponds to a low supply voltage (compared to a voltage of 5 Volts considered high). For example, the excitation voltage of the Wheatstone bridge 6 can be set at 2.5 V, or 2.2 V, or preferably at 2.048 V, in order to be able to power the Wheatstone bridge 6 with the voltage supplied by the cell 3. The voltage 2.048 V has the particularity of being able to be generated directly by a digital / analog converter of a microcontroller of the electronic control unit 5. Alternatively, the input terminals EPI, EP2 can be coupled to the electronic control unit 5, by connections 113, 114.Thus, the excitation voltage Vexe of the Wheatstone bridge 6 can be provided by the unit of . electronic control 5. For example, the electronic control unit 5 may be electrically coupled, by connections not shown for the sake of simplification, to the cell 3.

[0041] Furthermore, the first and second output terminals SP1, SP2 are coupled to the electronic control unit 5, by wired connections 8, 9. The electronic control unit 5 is configured to measure an output voltage Vout of the Wheatstone bridge 6. The output voltage Vout can be taken from the output terminals SP1, SP2 of the Wheatstone bridge 6. Furthermore, the electronic control unit 5 is configured to detect a deformation of the packaging 2 when the output voltage Vout is different from a reference voltage threshold Vref. Detection is understood to mean a measurement of a parameter representative of a deformation of the packaging 2. For example, the representative parameter is the output voltage Vout of the Wheatstone bridge 6. For example, the electronic control unit 5 can be configured to measure a deformation of the packaging 2 from the measured output voltage Vout.

[0042] In particular, the Wheatstone bridge 6 comprises a variable resistor R3 whose value is controlled by the electronic control unit 5. In other words, the electronic control unit 5 is configured to modify the value of the variable resistor R3. It is also said that the electronic control unit 5 can adjust the value of the variable resistor R3 or set the value of the variable resistor R3 to a predefined value, or that the electronic control unit 5 can assign, to the variable resistor R3, a predefined resistance value. The variable resistor R3 is intended to reduce, and in particular to correct, the effects of temperature on the detection of the deformation of the packaging 2.That is to say that many factors can intervene in the deformation of the packaging 2, and the detection device 1 makes it possible to detect a deformation of the packaging 2 only due to some of them, and more particularly those which appear during an abnormal operation of the cell 3. In general, the deformation of the packaging 2 can come either, during normal operation of the cell 3, from a mechanical expansion caused by a rise in temperature, or from an abnormal operation of the cell 3, by an abnormal accumulation of gas, caused for example by an overcharge, an excessive discharge or the start of thermal runaway. The variable resistor R3 will make it possible to identify any deformations due to the temperature when the cell 3 of battery 30 is in a normal operating state and at a specific temperature.Normal operating state means a cell 3 of battery 30 having a constant state of charge SoC and which is only subjected to mechanical stresses representative of its environment, i.e. stresses caused under normal operating conditions. In other words, the normal operating state may cor . respond to battery cell 30 charge states between 0 and 100% within a temperature range recommended by the manufacturer (usually between -20°C and 60°C) for a cell without defects.

[0043] The variable resistor R3 makes it possible to reset the “zero” on the output signal of the Wheatstone bridge 6, that is to say that it makes it possible to obtain an output voltage Vout equal to, or close to, the reference voltage threshold Vref. It is considered that when the output voltage Vout is equal to, or close to, the reference voltage threshold Vref, the deformation is zero or negligible, or that the deformation is due to the effects of the temperature on the package 2 while the cell 3 is in the normal operating state, such as for example a mechanical expansion of the package 2 due to an increase in the temperature of the package 2. In this case, the cell 3 is not necessarily in the abnormal operating state, and this mechanical expansion is considered as natural. Generally speaking, the output voltage Vout is a function, in particular, of the values ​​of the variable resistor R3 and of the resistance Rx of the strain gauge 7.In other words, by changing the value of the variable resistor R3, we change the value of the output voltage Vout.

[0044] The deformation e is usually expressed in pm / m. Equations 1 to 4 which relate the deformation to the parameters of the Wheatstone bridge 6 and the tensions are as follows:

[0045] [Math.l] „ _ Vout'xR3x{Rl+R2)+Vexc^(.RtxR3 X~ VexcxRl-Vmitx ( RI+R2 )

[0046] (equation 1) where: - RI is the first resistance of the Wheatstone bridge 6 (in Ohm); - R2 is the second resistance of the Wheatstone bridge 6 (in Ohm); - R3 is the variable resistance (in Ohm); - Vout is the output voltage of the Wheatstone bridge 6 (in Volts); - Vexe is the excitation voltage of the Wheatstone bridge 6 (in Volts); - Rx is the resistance of the strain gauge 7 (in Ohm) subjected to deformation or affected by temperature (or both).

[0047] The deformation e can be expressed according to the following equation 2:

[0048] [Math.2] _ Rx-Rnom Rnomxk

[0049] (equation 2) where: - Rnom is the nominal value of the strain gauge 7 (in Ohm); - k is the gauge factor given by the manufacturer (in m / pm), generally k = 2.

[0050] The nominal value Rnom of the resistance Rx corresponds to the upper limit of the measuring range of the strain gauge 7. In other words, the resistance Rx of the strain gauge 7 can vary from 0 to Rnom.

[0051] In the case where the reference voltage threshold Vref is equal to 0 V, and when the output voltage Vout is equal to the reference voltage threshold Vref, i.e. equal to 0 V, then according to equation 1, we obtain the following equation 3:

[0052] [Math.3] »

[0053] (equation 3) Advantageously, we can choose RI = R2, and we obtain the following equation 4:

[0054] [Math.4] Rx = R3

[0055] (equation 4)

[0056] Thus, when the package 2 is in an undeformed state, i.e. e = 0 pm / m, then according to equation 2, we obtain Rx = Rnom.

[0057] Thus, when the value of the variable resistor R3 is modified, so as to obtain an output voltage Vout equal to 0 V, then, according to equation 1, the relationship Rx = R3 (equation 4) is obtained. If the package 2 is in the undeformed state, then the value of the variable resistor R3 which made it possible to obtain the output voltage Vout = 0 V characterizes the undeformed state of the package 2. Generally, when the cell 3 is in the normal operating state, the value of the variable resistor R3 which made it possible to obtain the output voltage Vout = Vref characterizes the normal operating state of the cell 3. It will be noted that when the cell 3 is in the normal operating state, and depending on the temperature value of the package 2, the package 2 may be in a deformed state due to mechanical expansion.

[0058] Furthermore, when the output voltage Vout is equal to the reference voltage threshold Vref, the values ​​of the variable resistor R3 and the resistor Rx are equal. Thus, when the cell 3 is in the normal operating state, and the values ​​of the variable resistor R3 and the resistor Rx are equal, the output voltage Vout is equal to the reference voltage threshold Vref. Furthermore, when the package 2 is in a deformed state, the value of the resistor Rx changes, and if the variable resistor R3 does not change, the output voltage Vout also changes, i.e. the voltage Vout is different from the reference voltage threshold Vref. When the voltage Vout is different from the reference voltage threshold Vref, a deformation of the package 2 is detected. The reference voltage threshold Vref may be equal, for example, to 0 V, or for example to Vexc / 2 (where Vexe corresponds to the excitation voltage of the Wheatstone bridge 6).When the reference voltage threshold Vref is equal to Vexc / 2, it is . possible to measure deformations in both directions (stretching and compression). For example, the excitation voltage Vexe can be set to 2.048 V and the reference voltage threshold Vref set to 1.024 V, in particular to be able to detect deformation of package 2 in compression and stretching.

[0059] Since the cell 3 can undergo temperatures between -20°C and 60°C, and since the strain gauge 7 is sensitive to temperature, it is useful to take the temperature into account for the detection of the deformation of the package 2.

[0060] Thus, the device 1 comprises a temperature sensor 10 and a memory 11. The temperature sensor 10 is configured to measure a current temperature Te of the packaging 2. Furthermore, the sensor 10 is coupled to the electronic control unit 5, by a connection 12, to provide the unit 5 with information on the temperature of the packaging 2. The temperature sensor 10 may be a sensor of the NTC type (i.e. with a negative temperature coefficient, or NTC, Negative Temperature Coefficient in English).

[0061] The memory 11 is coupled to the electronic control unit 5, by a connection 13, so as to exchange digital data with the unit 5. The memory 11 can be printed on the card 100. More particularly, the memory 11 is configured to store a correspondence table 14 comprising values ​​of the variable resistor R3 associated respectively with temperatures Ti, in particular with temperatures Ti of the package 2. The temperatures Ti correspond to different current temperatures Te of the package 2 when the package 2 is placed in distinct temperature conditions. In particular, the values ​​of the variable resistor R3, in the correspondence table 14, correspond to temperatures Ti for which the cell 3 of the battery 30 is in the normal operating state. For example, the temperatures Ti of the correspondence table 14 are between -20°C and +60°C.According to another example, the temperatures Ti of the correspondence table 14 are distinct two by two by 5°C.

[0062] The electronic control unit 5 is further configured to determine the current temperature Te of the package 2 from the temperature sensor 10, and to place the value of the variable resistor R3 at the value associated with the current temperature Te in the correspondence table 14. Thus, for a current temperature Te, if the measured output voltage Vout is equal to the reference threshold Vref, the cell 3 is in the normal operating state. If, on the contrary, the output voltage Vout is different from the reference voltage threshold Vref, then a deformation of the package 2 is detected. In this case, the cell 3 is in the abnormal operating state. Thus, the device 1 can detect a deformation of the package 2 caused by an abnormal operation of the cell 3.

[0063] Thus, the device 1 makes it possible to detect a deformation of a package 2 of a cell 3 of battery 30 by freeing itself from the influence of temperature on the measuring devices, in particular on the strain gauge 7. Furthermore, since the deformation e can be calculated from the value of the resistance Rx of the strain gauge 7, according to equation 2, and since the resistance Rx of the strain gauge 7 can be calculated from the value of the output voltage Vout, according to equation 1, the electronic control unit 5 is configured to calculate the deformation e from the output voltage Vout. In other words, the electronic control unit 5 is configured to measure a deformation of the packaging 2 from the measured output voltage Vout.

[0064] Advantageously, the additional resistors RI, R2 are produced on the same semiconductor substrate and the variable resistor R3 is produced on the same semiconductor substrate.

[0065] For example, the resistance Rx of the strain gauge 7 may have a nominal value Rnom equal to 350 Ohms. Other strain gauges 7 may have a nominal value Rnom equal to 120 Ohms or equal to 1000 Ohms. In general, the variations in the resistance Rx of the strain gauge 7 are a few milliohms. In this case, the variable resistor R3 is preferably a digital potentiometer having a nominal value equal to that of the strain gauge 7, and whose sensitivity corresponds to a few milliohms.

[0066] In [Fig. 2], another embodiment of the detection device 1 is shown. In this embodiment, the variable resistor R3 has a first terminal R3a electrically coupled to the second output terminal SP2, i.e. to a terminal of the strain gauge 7, via a first additional resistor R4. Furthermore, the variable resistor R3 has a second terminal R3b electrically coupled to the second output terminal SP2, i.e. to the terminal of the strain gauge 7, via a second additional resistor R5. Preferably, the value of the second additional resistor R5 is strictly lower than that of the first additional resistor R4. This embodiment is particularly suitable for resistors Rx of a strain gauge 7 having a nominal value of 350 Ohms and a sensitivity of a few milliohms.This embodiment makes it possible to obtain a variable resistor R3 having a higher nominal value, for example equal to 5 kOhms, and therefore a better precision around the nominal value of the strain gauge 7. If for example we imagine having 256 possibilities of adjustment of the variable resistor R3 (equivalent to steps of approximately 19.5 ohms between 0 and 5 kOhms), we can obtain a variable resistor R3 by varying from 334 ohms up to approximately 358 ohms around the value of 350 Ohms. In this embodiment, we obtain the relationship defined by the following equation 5: .

[0067] [Math.5] “ ( T / ÔZ / wT + R5 )

[0068] (equation 5) where: - R4 is the first additional resistance of the Wheatstone bridge 6 (in Ohm); - R5 is the second additional resistance of the Wheatstone bridge 6 (in Ohm); - Req is the equivalent resistance (in Ohm) that replaces the variable resistor R3 in the previous equation 1.

[0069] For example, we can choose R4 = 3 kOhms and R5 = 375 Ohms. Thus, we can choose a variable resistor R3 whose resistance value can vary between 0 and 5 kOhms.

[0070] Furthermore, a method for detecting a deformation of the packaging 2 of a battery cell 30 can be implemented by the device 1 which has just been described. The method comprises the following main steps: a measurement of a current temperature Te of the packaging 2; an access to the correspondence table 14 of the device 1; and a placement of a value of the variable resistor R3 of the device 1 at a value associated with the current temperature Te in the correspondence table 14.

[0071] The method may further comprise a measurement of the output voltage Vout of the Wheatstone bridge 6 of the device 1; and a detection of a deformation of the package 2 when the output voltage Vout is different from the reference voltage threshold Vref. The method may also comprise a measurement of a deformation of the package 2 from the measured output voltage Vout.

[0072] For example, before accessing the correspondence table 14, the method comprises: creating the correspondence table 14 and recording, in the memory 11 of the device, the correspondence table 14.

[0073] The creation of the correspondence table may comprise: for each temperature Ti of the correspondence table 14: a placement of the package 2 at a temperature corresponding to the temperature Ti of the correspondence table 14; a measurement of the output voltage Vout of the Wheatstone bridge 6; a placement of the value of the variable resistor R3 at a value associated with the temperature Ti so that the output voltage Vout is equal to the reference voltage threshold Vref corresponding to a normal operating state of the cell 3 of the battery 30; and a recording, in the correspondence table 14, of the value of the variable resistor R3 associated with the temperature Ti.

[0074] When creating the correspondence table 14, the cell 3 is in the normal operating state. Then the package 2 is placed at different temperatures Ti. That is to say that the package 2 is exposed to several temperatures Ti. Advantageously, at each new temperature Ti a stabilization time of the temperature temperature is carried out. More particularly, the temperature stabilization time is carried out before a new measurement of the output voltage Vout. The stabilization time makes it possible to expose and stabilize the entire cell 3 and the battery 30, as well as the electronics of the device 1 at the same temperature as that of the package 2, to be close to the real conditions of use (the electronic components of the device 1 can also be affected by the temperature). Then, at each temperature Ti, the value of the variable resistor R3 is modified in order to bring the output voltage Vout equal to, or as close as possible to, the value of the reference voltage threshold Vref for which the cell 3 is in the normal operating state. Then, for each temperature Ti, the temperature Ti measured by the temperature sensor 10 and the modified value of the variable resistor 3 associated with the temperature Ti are recorded in the correspondence table 14.The modified value recorded corresponds to the value that was set, for example a value between 0 and 255 when the variable resistor R3 is a digital potentiometer. Thus, a correspondence table 14 is obtained comprising a list of temperatures Ti and a list of values ​​of the variable resistor R3 associated respectively with the temperatures Ti in the list. This correspondence table 14 will make it possible to modify the value of the variable resistor R3 according to each current temperature Te measured by the temperature sensor 10.

[0075] By proceeding in this way, the effects of temperature on the detection or measurement of the deformation of the packaging 2 can be reduced or cancelled during the step of adjusting the value of the variable resistor R3 from the correspondence table 14, which can be likened to a calibration step. These effects cover in particular the influence of temperature on the strain gauge, the effect of temperature on the other elements of the measuring electronics, but also the effect of temperature on the cell(s) 3, and on the battery 30 through the natural effects of mechanical expansion of its various constituents causing deformations of the packaging 2 that one does not wish to detect / measure.In a need to detect and measure abnormal deformations of the cell / battery, it is indeed important to target the detection only on abnormal phenomena, for example the sign of an abnormal accumulation of gas caused for example by an overcharge, an excessive discharge or the start of thermal runaway.

[0076] Advantageously, the value of the variable resistor R3 can be modified during use of the battery 30, and at each measurement of the output voltage Vout, in order to minimize the error in the measurement of the output voltage Vout due to the temperature.

[0077] The invention which has just been described makes it possible to limit the influence of temperature on the strain gauge and on the electronics of the device. Advantageously, one does not does not calculate the temperature drift of the strain gauge and it is not corrected by calculation either, but the value of a variable resistance of the Wheatstone bridge is modified to recalibrate the Wheatstone bridge, in order to remain within a measurement range without losing resolution (there is no reduction in gain). More generally, a self-calibration procedure of a gauge is set up by a device attached to the battery cell. In addition, the simple detection of a deformation makes it possible to highlight a malfunction of the battery which may be due to different parameters, such as gas release or thermal runaway, without having to calculate these.

Claims

Claims

1. Device for detecting a deformation of a packaging (2) of a battery cell (3), comprising: - a measuring circuit (4) comprising a Wheatstone bridge (6) itself comprising a strain gauge (7) having a resistance (Rx) varying as a function of a deformation of the packaging (2), and - an electronic control unit (5) configured to: • measure an output voltage (Vout) of the Wheatstone bridge (6), and for • detect deformation of the packaging (2) when the output voltage (Vout) is different from a reference voltage threshold (Vref), characterized in that the Wheatstone bridge (6) comprises a variable resistor (R3) whose value is controlled by the electronic control unit (5), and in that the device comprises: - a temperature sensor (10) configured to measure a temperature of the packaging (2); and - a memory (11) in which is stored a correspondence table (14) comprising values ​​of the variable resistance (R3) associated respectively with temperatures for which the battery cell (3) is in a normal operating state; the electronic control unit (5) being configured to: - determine a current temperature from the temperature sensor (10), and for - set the value of the variable resistor (R3) to the value associated with the current temperature in the correspondence table (14).

2. Device according to claim 1, wherein, the control unit electronics (5) is configured to measure a deformation of the packaging (2) from the measured output voltage (Vout).

3. Device according to claim 1 or 2, wherein the Wheatstone bridge (6) is electrically coupled to the battery cell (3) and an excitation voltage (Vexe) of the Wheatstone bridge (6) is supplied by the battery cell (3).

4. Device according to claim 1 or 2, wherein the Wheatstone bridge (6) is electrically coupled to the electronic control unit (5) and an excitation voltage (Vexe) of the Wheatstone bridge (6) is provided by the electronic control unit (5).

5. A device according to any one of claims 1 to 4, wherein the Wheatstone bridge (6) comprises first and second resistors (RI, R2) electrically coupled together in series, the variable resistor (R3) and the strain gauge (7) being electrically coupled together in series and electrically coupled in parallel with the first and second resistors (RI, R2).

6. Device according to claim 5, in which the first and second resistors (RI, R2) are produced on the same semiconductor substrate and the variable resistor (R3) is produced on the same semiconductor substrate.

7. Device according to any one of claims 1 to 6, wherein the variable resistor (R3) has a first terminal electrically coupled to a terminal of the strain gauge (7) via a first additional resistor (R4), and a second terminal electrically coupled to the terminal of the strain gauge (7) via a second additional resistor (R5), the value of the second additional resistor (R5) being strictly less than that of the first additional resistor (R4).

8. Device according to any one of claims 1 to 7, wherein the temperatures of the correspondence table (14) are between -20°C and +60°C.

9. Device according to any one of claims 1 to 8, in which the temperatures of the correspondence table (14) are distinct two by two by 5°C.

10. Device according to any one of claims 1 to 9, in which the battery is of the lithium-ion type.

11. Method for detecting a deformation of a package (2) containing a battery cell (3), using a detection device according to any one of the preceding claims, characterized in that the method comprises: • a measurement of a current temperature of the packaging (2); • access to the correspondence table (14) of the device; • a placement of a value of the variable resistor (R3) of the device at a value associated with the current temperature in the correspondence table (14); • a measurement of an output voltage (Vout) of the Wheatstone bridge (6) of the device; and • a detection of a deformation of the packaging (2) when the output voltage (Vout) is different from a reference voltage threshold (Vref).

12. Method according to claim 11, comprising a measurement of a deformation of the packaging (2) from the measured output voltage (Vout).

13. Method according to claim 11 or 12, comprising, before accessing the correspondence table (14): - a creation of the correspondence table (14) comprising, for each temperature of the correspondence table (14): • a placement of the packaging (2) at a temperature corresponding to the temperature of the correspondence table (14) • a measurement of the output voltage (Vout) of the Wheatstone bridge (6); • a placement of the value of the variable resistor (R3) at a value associated with the temperature so that the output voltage (Vout) is equal to a reference voltage threshold (Vref) corresponding to a normal operating state of the battery cell (3); and • a recording, in the correspondence table (14), of the value associated with the temperature; and a recording, in the memory (11) of the device, of the correspondence table (14)

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