DEVICE AND METHOD FOR DETECTING A DEFORMATION OF A BATTERY CELL PACKAGING

Description

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 the packaging of such a cell. STATE OF THE ART

[0002] Currently, small batteries, also called "Smart Cells" in English, are used. This generic term describes a battery cell, such as a lithium-ion or Li-ion battery, equipped with a battery management system (BMS) dedicated to self-measurement, self-diagnosis, and self-balancing of the battery. An important aspect of self-diagnosis is monitoring the cell's safety status. Furthermore, small batteries generally comprise one or more cells housed within an airtight package. For example, the deformation of a Li-ion cell's packaging can be studied by analyzing the signal from a strain gauge applied to its surface.Deformation can, in fact, be a sign of abnormal gas accumulation that can lead to swelling of the packaging, caused, for example, by overloading, excessive discharge, or the onset of thermal runaway, which can cause the packaging to expand. Under nominal cell operating conditions, deformation can be related to the cell's state of charge (SoC) or its state of health (SoH).

[0003] Strain gauges are extremely sensitive to temperature; their signal changes due to both deformation and temperature. The use of so-called self-compensating gauges, designed to drift with temperature to compensate for the thermal expansion of the material they are applied to, is insufficient to eliminate the influence of temperature on the usable signal. This is because a battery cell is a rather heterogeneous object, composed of different metals, electrolyte, and packaging that can be metallic or a thin layer of aluminum coated with polymer on both sides. Furthermore, the self-compensation of these gauges is only effective within a limited temperature range, generally between 10°C and 50°C.However, for battery cells, the temperature can vary from -20°C to 60°C, and it may be useful to know the deformations of the packaging at the limit operating temperatures of a battery.

[0004] 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 hermetically sealed package, because access to the inside of the cell is not possible.

[0005] Another example is the use of two gauges, one of which is a reference gauge. For instance, there are gauges called "dummy gauges," which are essentially 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 the element whose deformation is to be measured. However, dummy gauges are bulky systems.

[0006] To improve strain gauge measurements, measurement systems using high-resolution digital converters (24 bits or higher) can be employed. However, these techniques are primarily intended for laboratory use, mainly because most of these converters are powered by 5 volts from a 220 V high-voltage source. These converters are not suitable for battery power, especially from a small battery providing a 2.5-volt low-voltage supply.

[0007] Examples include Chinese patent application CN112763136A, which discloses a power battery block pressure alarm system, and German patent application DE102017108708A1, which discloses a battery charge state monitoring system based on battery expansion.

[0008] We can also cite systems that use strain gauge signal calibration; for example, US patent application US3130578, which discloses a system comprising a Wheatstone bridge for measuring the signal of a strain gauge equipped with a control circuit operated by switches to short-circuit a resistor in the Wheatstone bridge. However, this system uses control circuits and switches that are complex to implement and, moreover, consume electrical power.

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

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

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

[0012] The Wheatstone bridge includes a variable resistor whose value is controlled by the electronic control unit, and the device includes: a temperature sensor configured to measure a temperature of the packaging; and a memory in which is stored a lookup 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 place the value of the variable resistance to the value associated with the current temperature in the lookup table.

[0014] This provides a device that can detect deformation of a battery cell packaging, eliminating the influence of temperature on detection devices. Such a device is particularly well-suited for integration, along with the battery, into mobile equipment, such as handheld devices.

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

[0016] The process includes: a measurement of a current temperature of the packaging; access to the device lookup table; placement of a value of the variable resistance of the device to a value associated with the current temperature in the lookup table; a measurement of an output voltage of the device's Wheatstone bridge; 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, features and advantages of the invention will become clearer from the detailed description of an embodiment thereof, which is illustrated by the following accompanying drawings in which: There figure 1 schematically represents an embodiment of a device for detecting deformation of a battery cell packaging; The figure 2 schematically represents another embodiment of the detection device illustrated in the figure 1 .

[0018] The drawings are given as examples and are not limiting to the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. DETAILED DESCRIPTION

[0019] Before beginning a detailed review of embodiments and implementations of the invention, optional features that may be used in combination or alternatively are stated below.

[0020] In one example, the electronic control unit is configured to measure packaging deformation from the measured output voltage.

[0021] In one example, the Wheatstone bridge is electrically coupled to the battery cell, and the battery cell provides an excitation voltage for the Wheatstone bridge. A device specifically designed for integration with the battery cell is provided within electrically powered equipment, such as portable devices.

[0022] In one example, the Wheatstone bridge is electrically coupled to the electronic control unit and an excitation voltage for the Wheatstone bridge is supplied by the electronic control unit.

[0023] According to one example, the Wheatstone bridge includes first and second resistors electrically coupled together in series, the variable resistor and strain gauge being electrically coupled together in series and electrically coupled in parallel to the first and second resistors.

[0024] In one example, the first and second resistors are fabricated on the same semiconductor substrate, and the variable resistor is also fabricated on the same semiconductor substrate. This further limits the effect of temperature on the detection device components.

[0025] In one example, the variable resistor has a first terminal electrically connected to one terminal of the strain gauge via a first additional resistor, and a second terminal electrically connected to the strain gauge terminal via a second additional resistor, the value of the second additional resistor being strictly lower than that of the first. Such a device is suitable for strain gauges with a low nominal resistance value, for example, 120 ohms, 350 ohms, or 1000 ohms.

[0026] As an example, the temperatures in the correspondence table range from -20°C to +60°C.

[0027] According to one example, the temperatures in the correspondence table are distinct in pairs by 5°C.

[0028] In one example, the battery is of the lithium-ion type.

[0029] According to one example, the process includes measuring a deformation of the packaging from the measured output voltage.

[0030] According to one example, the process includes, before accessing the lookup table: a creation of the lookup table including, for each temperature in the lookup table: ∘ a placement of the packaging at a temperature corresponding to the temperature in the lookup table; ∘ a measurement of the output voltage of the Wheatstone bridge; ∘ a placement of the value of the variable resistor at 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 recording, in the lookup table, of the value associated with the temperature; and a recording, in the device memory, of the lookup table.

[0031] It is specified that within the framework 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 component between A and B. Thus, these expressions refer to an electrical connection between two elements, this connection being either direct or indirect; 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 along the path connecting A to B, this path being either or not including other electrical equipment.

[0032] Conversely, in the context of the present invention, the term "directly electrically coupled" refers to a direct electrical connection between two elements. This means that between a first device A and a second device B that are directly electrically coupled, no other equipment is present, other than an electrical connection or several electrical connections.

[0033] On the figure 1Figure 1 shows a deformation detection device for a battery cell 30 casing 2. In other words, the battery 30 comprises a casing 2 in which one or more cells 3 are housed. The casing 2 can be cylindrical, for example, prismatic, cylindrical with a circular cross-section, or parallelepiped-shaped. A cylinder, or cylindrical shape, is defined as a solid bounded by an external surface, called the cylindrical surface, 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 is ​​a polygon and the planes are parallel, the cylinder is a prism. A parallelepiped is defined as a solid bounded by six parallelogram faces. In the case of battery cells, the parallelepiped is typically a prism whose directrix is ​​a rectangle. Packaging 2 can be flexible, such as a prismatic or parallelepiped-shaped bag, or semi-rigid, such as a cylindrical, circular, prismatic, or parallelepiped-shaped container. Flexible packaging is defined as packaging that deforms under its own weight. Semi-rigid packaging is defined as packaging that does not deform under its own weight and can deform within 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 flexible enough to allow for deformation. For example, battery 30 is a lithium-ion type. A lithium-ion battery comprises one or more cells 3, called lithium-ion cells. Each cell 3 has two electrodes separated by an electrolyte configured to generate charge carriers, specifically lithium ions.

[0034] Device 1 includes a measuring circuit 4 and an electronic control unit 5. More specifically, the measuring circuit 4 includes a Wheatstone bridge 6. The Wheatstone bridge 6 includes first and second resistors R1, R2, and a strain gauge 7. In particular, the strain gauge 7 is in contact with the battery pack 2 of the battery 30. Furthermore, the Wheatstone bridge 6 includes first and second input terminals EP1, EP2 and first and second output terminals SP1, SP2. The first resistor R1 has its terminals electrically coupled, preferably directly, to the first input terminal EP1 and the first output terminal SP1, respectively. The second resistor R2 has its terminals electrically coupled, preferably directly, to the first output terminal SP1 and the second input terminal EP2, respectively.More specifically, the first and second resistors R1, R2 each have a constant resistance value. For example, the first and second resistors R1, R2 have equal resistance values.

[0035] The strain gauge 7 has a resistance Rx that varies according to the 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 deformation. The resistor Rx of the strain gauge 7 has its terminals electrically coupled, preferably directly, to the first input terminal EP1 and the second output terminal SP2, respectively. The strain gauge 7 emits a signal that changes according to the deformation of the package 2. In particular, the value of the resistance Rx varies according to the deformation of the package 2. Thus, the Wheatstone bridge 6 allows the deformation of the package 2 to be measured by measuring the signal from the strain gauge 7.

[0036] The measuring circuit 4 and the electronic control unit 5 can be printed on a printed circuit board 100, called a "Printed Circuit Board" in English.

[0037] The first and second input terminals EP1 and EP2 are configured to receive an excitation voltage Vexc. This excitation voltage Vexc can be supplied by the board 100. For example, a Vexc excitation voltage of 5V can be provided. Preferably, the board 100 is electrically coupled to battery cell 3, and the excitation voltage Vexc is supplied by battery cell 30. This allows the board 100 and battery 30 to be integrated into the same device. The board 100 and battery 30 assembly is therefore compact. For example, the input terminals EP1 and EP2 are respectively coupled to output terminals 101 and 102 of battery 30 via connections 103 and 104. The excitation voltage Vexc of the Wheatstone bridge 6 can be supplied by battery cell 30.

[0038] Preferably, the voltage supplying the electronic components of device 1, namely the temperature sensor 10, the electronic control unit 5, and the memory 11, comes from 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 to 2.5 V, or 2.2 V, or preferably to 2.048 V, in order to be able to supply the Wheatstone bridge 6 with the voltage supplied by the cell 3. The 2.048 V voltage 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 EP1, EP2 can be coupled to the electronic control unit 5, by connections 113, 114.Thus, the excitation voltage Vexc of the Wheatstone bridge 6 can be supplied by the electronic control unit 5. For example, the electronic control unit 5 can be electrically coupled, by connections not shown for the sake of simplification, to the cell 3.

[0039] Furthermore, the first and second output terminals SP1, SP2 are connected to the electronic control unit 5 via wire 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. In addition, the electronic control unit 5 is configured to detect deformation of the package 2 when the output voltage Vout differs from a reference voltage threshold Vref. Detection is understood to mean the measurement of a parameter representative of a deformation of the package 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 package 2 based on the measured output voltage Vout.

[0040] In particular, the Wheatstone bridge 6 includes 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 change 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, set the value of the variable resistor R3 to a predefined value, or assign a predefined resistance value to the variable resistor R3. The variable resistor R3 is intended to reduce, and in particular correct, the effects of temperature on the detection of deformation of the packaging 2.This means that many factors can contribute to the deformation of the packaging 2, and the detection device 1 can only detect deformation of the packaging 2 due to some of these factors, particularly those that occur during abnormal operation of the cell 3. Generally, deformation of the packaging 2 can result, either during normal operation of the cell 3, from mechanical expansion caused by a temperature rise, or during abnormal operation of the cell 3, from an abnormal accumulation of gas, caused, for example, by overcharging, excessive discharge, or the onset of thermal runaway. The variable resistor R3 will identify any temperature-related deformations when the battery cell 3 is in normal operation and at a specific temperature.A normal operating state is defined as a battery cell 30 with a constant state of charge (SoC) and subjected only to mechanical stresses representative of its environment, i.e., stresses induced under normal operating conditions. In other words, a normal operating state can correspond to 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.

[0041] The variable resistor R3 resets the output signal of the Wheatstone bridge 6 to zero, meaning it ensures an output voltage Vout equal to, or close to, the reference voltage threshold Vref. When the output voltage Vout is equal to, or close to, the reference voltage threshold Vref, the deformation is considered to be zero or negligible, or that the deformation is due to the effects of temperature on the package 2 while the cell 3 is in its normal operating state. This could be due to mechanical expansion of the package 2 caused by a temperature increase. In this case, the cell 3 is not necessarily in an abnormal operating state, and this mechanical expansion is considered normal. Generally, the output voltage Vout depends, in particular, on the values ​​of the variable resistor R3 and 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.

[0042] The strain ε is usually expressed in µm / m. Equations 1 to 4, which relate the strain to the parameters of the Wheatstone bridge 6 and the stresses, are as follows: Rx = Vout × R 3 × R 1 + R 2 + Vexc × R 1 × R 3 Vexc × R 2 − Vout × R 1 + R 2 Or : R1 is the first resistance of the Wheatstone bridge 6 (in Ohms); R2 is the second resistance of the Wheatstone bridge 6 (in Ohms); R3 is the variable resistance (in Ohms); Vout is the output voltage of the Wheatstone bridge 6 (in Volts); Vexc is the excitation voltage of the Wheatstone bridge 6 (in Volts); Rx is the resistance of the strain gauge 7 (in Ohms) subjected to deformation or affected by temperature (or both).

[0043] The deformation ε can be expressed according to the following equation 2: ε = Rx − Rnom Rnom × k Or : Rnom is the nominal value of strain gauge 7 (in Ohm); k is the gauge factor given by the manufacturer (in m / µm), usually k = 2.

[0044] The nominal value Rnom of the resistance Rx corresponds to the upper limit of the measurement range of strain gauge 7. In other words, the resistance Rx of strain gauge 7 can vary from 0 to Rnom.

[0045] 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: Rx = R 1 × R 3 R 2

[0046] Advantageously, we can choose R1 = R2, and we obtain the following equation 4: Rx = R 3

[0047] Thus, when packaging 2 is in an undeformed state, i.e. ε = 0 µm / m, then according to equation 2, we obtain Rx = Rnom.

[0048] Thus, when the value of the variable resistor R3 is changed to obtain an output voltage Vout equal to 0 V, then, according to equation 1, we obtain the relationship Rx = R3 (equation 4). If package 2 is in its undeformed state, then the value of the variable resistor R3 that resulted in the output voltage Vout = 0 V characterizes the undeformed state of package 2. In general, when cell 3 is in its normal operating state, the value of the variable resistor R3 that resulted in the output voltage Vout = Vref characterizes the normal operating state of cell 3. Note that when cell 3 is in its normal operating state, and depending on the temperature of package 2, package 2 may be in a deformed state due to mechanical expansion.

[0049] Furthermore, when the output voltage Vout is equal to the reference voltage threshold Vref, the values ​​of the variable resistor R3 and the resistance Rx are equal. Thus, when cell 3 is in its normal operating state, and the values ​​of the variable resistor R3 and the resistance Rx are equal, the output voltage Vout is equal to the reference voltage threshold Vref. However, when the package 2 is in a deformed state, the value of the resistance Rx changes, and if the variable resistor R3 does not change, the output voltage Vout also changes; that is, the voltage Vout is different from the reference voltage threshold Vref. When the voltage Vout is different from the reference voltage threshold Vref, deformation of the package 2 is detected. The reference voltage threshold Vref can be equal, for example, to 0 V, or for example to Vexc / 2 (where Vexc 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 Vexc can be set to 2.048 V and the reference voltage threshold Vref to 1.024 V, specifically to detect deformation of the package 2 under both compression and stretching. Since the cell 3 can withstand temperatures ranging from -20°C to 60°C, and since the strain gauge 7 is temperature-sensitive, it is useful to consider temperature when detecting deformation of the package 2.

[0050] Thus, the device 1 includes a temperature sensor 10 and a memory 11. The temperature sensor 10 is configured to measure a current temperature Tc of the package 2. In addition, the sensor 10 is coupled to the electronic control unit 5, by a connection 12, to provide the unit 5 with temperature information of the package 2. The temperature sensor 10 can be an NTC type sensor (i.e., with negative temperature coefficient).

[0051] The memory 11 is coupled to the electronic control unit 5 via a connection 13, enabling the exchange of digital data with the unit 5. The memory 11 can be printed onto the card 100. Specifically, the memory 11 is configured to store a lookup table 14 comprising values ​​of the variable resistor R3 associated with temperatures Ti, including temperatures Ti of the package 2. The temperatures Ti correspond to different current temperatures Tc of the package 2 when the package 2 is placed under different temperature conditions. In particular, the values ​​of the variable resistor R3 in the lookup table 14 correspond to temperatures Ti at which the battery cell 30 is in its normal operating state. For example, the temperatures Ti in the lookup table 14 range from -20°C to +60°C.According to another example, the temperatures Ti in the lookup table 14 are distinct in pairs by 5°C.

[0052] The electronic control unit 5 is further configured to determine the current temperature Tc of package 2 from the temperature sensor 10, and to set the value of the variable resistor R3 to the value associated with the current temperature Tc in the lookup table 14. Thus, for a given current temperature Tc, if the measured output voltage Vout is equal to the reference threshold Vref, cell 3 is in normal operating condition. If, on the other hand, the output voltage Vout differs from the reference voltage threshold Vref, then deformation of package 2 is detected. In this case, cell 3 is in abnormal operating condition. Thus, device 1 can detect deformation of package 2 caused by abnormal operation of cell 3.Thus, device 1 enables the detection of deformation in the packaging 2 of a battery cell 30, eliminating the influence of temperature on the measuring instruments, particularly the strain gauge 7. Furthermore, since the deformation ε can be calculated from 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 output voltage Vout, according to equation 1, the electronic control unit 5 is configured to calculate the deformation ε from the output voltage Vout. In other words, the electronic control unit 5 is configured to measure the deformation of the packaging 2 based on the measured output voltage Vout. Advantageously, the additional resistors R1 and R2 are fabricated on the same semiconductor substrate, and the variable resistor R3 is also fabricated on the same semiconductor substrate.

[0053] For example, the resistance Rx of strain gauge 7 might have a nominal value Rnom of 350 ohms. Other strain gauges 7 might have a nominal value Rnom of 120 ohms or 1000 ohms. Generally, the variations in the resistance Rx of strain gauge 7 are on the order of a few milliohms. In this case, the variable resistor R3 is preferably a digital potentiometer with a nominal value equal to that of strain gauge 7, and a sensitivity of a few milliohms.

[0054] On the figure 2Another embodiment of the detection device 1 is shown. In this embodiment, the variable resistor R3 has a first terminal R3a electrically connected 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 connected to the second output terminal SP2, i.e., to a terminal of the strain gauge 7, via a second additional resistor R5. Preferably, the value of the second additional resistor R5 is strictly less than that of the first additional resistor R4. This embodiment is particularly suitable for strain gauge 7 resistances Rx with a nominal value of 350 ohms and a sensitivity of a few milliohms.This embodiment allows for a variable resistance R3 with a higher nominal value, for example equal to 5 kOhms, and therefore better accuracy around the nominal value of the strain gauge 7. If, for example, we imagine having 256 possible adjustments for the variable resistance R3 (equivalent to steps of approximately 19.5 ohms between 0 and 5 kOhms), we can obtain a variable resistance R3 varying from approximately 334 ohms to 358 ohms around the value of 350 Ohms. In this embodiment, we obtain the relationship defined by the following equation 5: . Req = 1 R 3 + R 4 + 1 R 5 − 1 Or : R4 is the first additional resistance of the Wheatstone 6 bridge (in Ohm); R5 is the second additional resistance of the Wheatstone 6 bridge (in Ohm); Req is the equivalent resistance (in Ohm) which replaces the variable resistance R3 in the previous equation 1.

[0055] 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.

[0056] Furthermore, a method for detecting deformation of the packaging 2 of a battery cell 30 can be implemented by the device 1 just described. The method comprises the following main steps: measuring a current temperature Tc of the packaging 2; accessing the lookup table 14 of the device 1; and assigning a value of the variable resistance R3 of the device 1 to a value associated with the current temperature Tc in the lookup table 14.

[0057] The method may further include measuring the output voltage Vout of the Wheatstone bridge 6 of device 1; and detecting deformation of the package 2 when the output voltage Vout differs from the reference voltage threshold Vref. The method may also include measuring the deformation of the package 2 based on the measured output voltage Vout.

[0058] For example, before accessing the lookup table 14, the process includes: creating the lookup table 14 and recording the lookup table 14 in the device's memory 11.

[0059] The creation of the lookup table may include: for each temperature Ti in the lookup table 14: a placement of the package 2 at a temperature corresponding to the temperature Ti in the lookup 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 battery cell 30; and a recording, in the lookup table 14, of the value of the variable resistor R3 associated with the temperature Ti.

[0060] During the creation of the lookup table 14, cell 3 is in its normal operating state. Then, package 2 is placed at different temperatures Ti. That is, package 2 is exposed to several temperatures Ti. Advantageously, a temperature stabilization period is performed at each new temperature Ti. More specifically, the temperature stabilization period is performed before a new measurement of the output voltage Vout. The stabilization period allows the entire cell 3 and battery 30, as well as the electronics of device 1, to be exposed and stabilized at the same temperature as package 2, to closely approximate real-world operating conditions (the electronic components of device 1 can also be affected by temperature).Then, at each temperature Ti, the value of the variable resistor R3 is adjusted to bring the output voltage Vout equal to, or as close as possible to, the reference voltage threshold Vref at which cell 3 is in its normal operating state. The lookup table 14 then records, for each temperature Ti, the temperature Ti measured by the temperature sensor 10 and the adjusted value of the variable resistor 3 associated with that temperature Ti. The recorded adjusted value corresponds to the set value, for example, a value between 0 and 255 when the variable resistor R3 is a digital potentiometer. This results in a lookup table 14 containing a list of temperatures Ti and a list of values ​​of the variable resistor R3 associated with the temperatures Ti in the list.This correspondence table 14 will allow the value of the variable resistance R3 to be modified according to each current temperature Tc measured by the temperature sensor 10.

[0061] 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 eliminated during the step of adjusting the value of the variable resistance R3 from the lookup table 14, which can be considered 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 measurement 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 components, causing deformations of the packaging 2 that we do not wish to detect / measure.In the 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 beginning of thermal runaway.

[0062] Advantageously, the value of the variable resistor R3 can be modified during battery operation and at each measurement of the output voltage Vout, in order to minimize the error in the output voltage measurement due to temperature. The invention described above makes it possible to limit the influence of temperature on the strain gauge and on the device's electronics. Advantageously, the temperature drift of the strain gauge is not calculated, nor is it corrected by calculation; instead, the value of a variable resistor in the Wheatstone bridge is modified to recalibrate the Wheatstone bridge, thus remaining within a measurement range without loss of resolution (there is no decrease in gain). More generally, a self-calibration procedure for a strain gauge is implemented using a device attached to the battery cell.Furthermore, the simple detection of a deformation makes it possible to highlight a battery malfunction that may be due to various parameters, such as gas release or thermal runaway, without having to calculate these.

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 stress 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 to • detect a deformation of the packaging (2) when the output voltage (Vout) is different from a reference voltage threshold (Vref), characterised in that the Wheatstone bridge (6) comprises a variable resistance (R3), the value of which 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 a lookup 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 to - place the value of the variable resistance (R3) at the value associated with the current temperature in the lookup table (14).

2. Device according to claim 1, wherein, the electronic control unit (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 (Vexc) 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 (Vexc) of the Wheatstone bridge (6) is supplied by the electronic control unit (5).

5. Device according to any one of claims 1 to 4, wherein the Wheatstone bridge (6) comprises first and second resistances (R1, R2) electrically coupled to one another in series, the variable resistance (R3) and the stress gauge (7) being electrically coupled to one another in series and electrically coupled in parallel from the first and second resistances (R1, R2).

6. Device according to claim 5, wherein the first and second resistances (R1, R2) are produced on one same semiconductor substrate and the variable resistance (R3) is produced on the same semiconductor substrate.

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

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

9. Device according to any one of claims 1 to 8, wherein the temperatures of the lookup table (14) are distinct in pairs of 5°C.

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

11. Method for detecting a deformation of a packaging (2) containing a battery cell (3), using a detection device according to any one of the preceding claims, characterised in that the method comprises: • a measurement of a current temperature of the packaging (2); • an access to the lookup table (14) of the device; • a placement of a value of the variable resistance (R3) of the device at a value associated with the current temperature in the lookup 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 lookup table (14): - a creation of the lookup table (14) comprising, for each temperature of the lookup table (14): • a placement of the packaging (2) at a temperature corresponding to the temperature of the lookup table (14); • a measurement of the output voltage (Vout) of the Wheatstone bridge (6); • a placement of the value of the variable resistance (R3) at a value associated with the temperature such 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 lookup table (14), of the value associated with the temperature; and - a recording, in the memory (11) of the device, of the lookup table (14).