Device and method for thermal monitoring of a battery

Abstract

A device for monitoring a battery (30), in particular a lithium-ion battery, to prevent thermal runaway, comprising the battery (30) having a plurality of cells (6) arranged next to one another within a housing (16) under a prestress in a transverse direction (8), wherein a measuring arrangement (36) is provided for detecting an expansion of at least one of the cells in the transverse direction (8), and the measuring arrangement (36) has a plurality of sensors (12) and an evaluation unit (18, 34), characterized in that the sensors (12) are each arranged between two cells (6) adjacent in the transverse direction (8) and are connected to the evaluation unit (18, 34), so that an expansion of one of the cells (6) in the transverse direction (8) is detected by the measuring arrangement (36) and monitored with regard to exceeding a critical value for the expansion, wherein the critical value indicates a potential occurrence of a thermal runaway,characterized in that a detection unit (40) is provided for detecting a current operating temperature of the battery (30) and the evaluation unit (18, 34) is arranged such that the critical value is set as a function of the current operating temperature.

Description

The invention relates to a device and a method for thermally monitoring a battery, in particular a lithium-ion battery, in order to avoid a so-called "thermal runaway".In rechargeable batteries, especially lithium batteries and in particular in high-voltage vehicle batteries, which are used for an electric traction motor, the problem of so-called "thermal runaway" is known. This is an exothermic chemical reaction within a battery cell, in which overheating as far as explosion of the cell or a fire occurs due to a self-boosting and heat-producing chemical process. Such a thermal runaway starts within a cell of a battery, for example due to an overload or a short circuit. If the temperature increased as a result exceeds a limit temperature, the self-boosting chemical process begins, which further heats the temperature of the cell until the cell is exploded or burned. This also influences adjacent cells which, owing to the higher heat, can likewise begin to burn. The propagating fire can then propagate very quickly to the entire battery and, in the case of a vehicle battery, to the vehicle.DE 10 2009 034 854 A1 and WO 2019 146 960 A1 disclose methods and devices for monitoring a state of charge of a battery.DE 10 2009 034 854 A1 provides for this purpose to record the change in at least one non-electrical physical variable of the battery as a measure of the state of charge. In particular, a volume change or a changing pressure is detected. In this case, lithium batteries with graphite as active material are monitored in particular, in which a change in the state of charge leads to a change in volume. To detect the change in volume, a housing delimiting a cell stack is provided, for example, with a plate which is movable on one side and forms an electrode. In the event of a change in volume, the distance to a second electrode changes by displacement of the movable plate. A change in capacitance caused thereby is detected.WO 2019,146,960 A1 describes a pressure sensor in various embodiments which is applied to the outside of a battery and detects a pressure change due to a change in volume.DE 10 2015 211 598 A1 discloses the arrangement of force sensors between two adjacent cells of a battery for battery monitoring.According to US 2006 / 0 246 345 A1, a piezoelectric sensor is arranged for detecting a pressure change between the cells of a battery.US 2017 / 0 324 110 A1 describes the arrangement of capacitive elements between the cells in order to detect expansions.Proceeding from this, the object of the invention is to specify a device and a method for monitoring a battery, especially a rechargeable battery (rechargeable battery) and in particular a lithium-ion battery, in order to avoid thermal runaway.The object is achieved according to the invention by a device having the features of claim 1 and by a method having the features of claim 13.The device has a rechargeable battery (rechargeable battery), in particular a lithium-ion battery, which has a plurality of, in particular, cuboidal cells, which are arranged next to one another within a housing under a bias voltage in a transverse direction. The device further comprises a measuring arrangement for detecting an extension of at least one of the cells in the transverse direction. For this purpose, the measuring arrangement has a plurality of, in particular capacitive, sensors and an evaluation unit. The sensors are each arranged between two cells adjacent in the transverse direction and are connected to the evaluation unit. When one of the cells extends in the transverse direction, a change in distance from the sensors and the evaluation unit is detected by this measuring arrangement. When using capacitive sensors, a change in capacitance is caused by the change in distance, which is evaluated by the evaluation unit.With this measuring arrangement, the battery is monitored with regard to the formation of a thermal runaway. As soon as a critical extent or distance change between two adjacent cells is detected which exceeds a critical value, this critical value being characteristic of the potential occurrence of a thermal runaway, a corresponding countermeasure is initiated. One such option is, for example, to reduce the load on the battery or to disconnect the battery from the rest of the (on-board) network, especially of a motor vehicle. The device, especially the evaluation unit, is designed and configured altogether for carrying out these steps.The critical value for the change in distance is generally greater than a change customary in operation as a result of normal, operationally dependent temperature fluctuations within an admissible operating temperature range.This measure therefore ensures overall predictive detection of a potentially occurring thermal runaway and reliably prevents such a thermal runaway from occurring. A particular advantage of the measuring arrangement is that the sensor, which is capacitive in particular, in each case performs an individual measurement between two cells adjacent in the transverse direction, so that each cell can therefore be individually monitored. This is of particular importance.The batteries considered here, especially vehicle batteries, are constructed in such a way that a plurality of cells are combined to form a cell module. Within a cell module, the individual cells are typically connected to one another in series, such that the voltage of the cell module results from the sum of the voltages of the individual cells. The cell module itself typically has a module housing. The individual cells combined in a cell module are typically held braced against one another within the module housing. Thus, a certain pressure is already exerted on the individual cells in the initial state. This achieves the highest possible packing density of the individual cells and overall a compact structure of the battery. A plurality of such cell modules are in turn interconnected to form the entire battery and are typically combined within a battery housing. The individual cell modules are typically also connected in series to achieve the desired battery voltage. Depending on the field of application, especially in a battery for supplying a motor vehicle's electric traction motor, the battery voltage and the corresponding supply voltage for the electric traction motor is typically several 100 volts, typically greater than 300 volts and, for example, in the range between 300 and 1,000 volts.If "cell" is mentioned here, this is to be understood as meaning both a single (galvanic) individual cell which has a (single) cathode and a (single) anode and a separator arranged therebetween. In addition, "cell" is also understood to mean the common arrangement of a plurality of such individual cells, in which the cathode-separator-anode layer structure is thus repeated periodically. If a plurality of such individual cells are used for the construction of a cell, the individual cells contained therein are preferably connected in parallel. The cell therefore has the voltage of a respective individual cell. A single cell typically has a voltage in the range of a few volts, for example in the range between 1 and 5 volts. Typical values for a lithium single cell are between 2 and 4.5 volts, depending on the materials used. In the present case, "cell" is understood to mean, in particular, an individual cell.The housing of a cell, also referred to below as a cell housing, consists, for example, of an inherently rigid and dimensionally stable, typically cuboidal, volume body. Alternatively, the housing of the cell is made of a flexible material, for example a (metal) foil.In the present case, "cell module" is understood to mean, in particular, a cell module in which, for example, 4 to 20, and in particular 4 to 14, cells are connected and arranged in series with one another.The individual monitoring of a respective cell by measuring the change in distance between two cells adjacent in the transverse direction has the particular advantage of a high sensitivity with respect to a malfunction of an individual cell, i.e. with respect to a potential occurrence of a thermal runaway within a cell. In contrast to monitoring systems as are known from the prior art, in which, for example, only the extent of the entire cell module (composite of cells) is determined in order to monitor the state of charge, the sensitivity is significantly higher. Only in this way is a reliable and reliable predictive detection of a thermal runaway ensured before it arises.In an expedient embodiment, a respective sensor and the evaluation unit are configured to detect a change in distance between two cells in the range between 1 μm and 100 μm and in particular between 1 μm and 50 μm. This ensures a high sensitivity and even very small expansions as a result of an increasing temperature can be detected reliably.If "change", for example a measured value of the sensor or a variable derived therefrom, such as the distance, is referred to here, the term "change" always refers to a base value or reference value in an initial state of the battery. Such an initial state is in particular a load-free state at a reference temperature of in particular 20°, for example. This reference or base value is detected and stored in particular by a calibration measurement. Such a calibration measurement is carried out, for example, for each individual battery or alternatively only on the basis of a reference battery to which the respective battery is structurally identical. Specifically, therefore, only a relative measurement or relative change is carried out / determined by the sensor and / or the evaluation unit without an exact absolute determination being necessary or being carried out.The sensor furthermore has a thickness, as viewed in the transverse direction, in the range from 150 μm to 500 μm and in particular a thickness in the range between 200 and 400 μm and especially a thickness of 300 μm. As a result, the required installation space for the cell module is only slightly increased and a compact design is furthermore ensured.The sensors are preferably planar, capacitive sensors. The area of the sensors corresponds, for example, to more than 5%, preferably more than 20%, of a base area of the respective cells which is oriented perpendicularly to the transverse direction.In a preferred embodiment, a sensor is arranged between each pair of cells, so that a sensor is arranged between each pair of cells. In general, the distance between two adjacent cells of a cell module is thus monitored with the aid of the measuring arrangement.In general, the evaluation unit is designed to compare the measured values, i.e. specifically the (capacitance) changes of the various sensors, with one another. Furthermore, the evaluation unit is designed to monitor these measured values of the sensors with regard to an uneven change (with respect to the aforementioned base value), wherein an uneven change of the measured values is evaluated as exceeding the critical value and a corresponding countermeasure is initiated.The individual measured values of the sensors are therefore compared relative to one another. This is based on the consideration that, for example, a strong change in a sensor indicates that a cell adjacent to this sensor is defective. In contrast, sensors which are assigned to cells which are not defective would experience a significantly smaller change, so that a conclusion can therefore be drawn from this relative comparison as to a defective cell. If a "non-uniform change" is mentioned here, this is understood to mean that the changes between two sensors deviate from one another by more than an admissible tolerance range, wherein the tolerance range is, for example, 10%, 20% or 30% with respect to the change.By individually evaluating the individual sensors, a localization of the defective cell is also possible and is preferably also carried out by the evaluation unit.According to the invention, a detection unit, in particular a temperature sensor, is additionally arranged for detecting a current operating temperature of the battery. The evaluation unit is furthermore configured such that the critical value is set as a function of the current operating temperature. The at least one temperature sensor is placed at a suitable measurement point directly on or in the battery. Preferably, a plurality of temperature sensors are provided and, in this case, a value derived from the plurality of measured temperatures, for example an average value, is determined as the current operating temperature.The consideration of the current operating temperature and the setting of the critical value, i.e. the value for the permissible change of the measurement value of the sensor with respect to its reference value, is based on the fact that the individual cells experience a permissible expansion during operation as a result of normal, operationally dependent temperatures. Thus, typically high load states, especially during the charging process, lead to temperature increases and corresponding expansions of the individual cells. These are therefore already taken into account by the analysis unit changing the critical value. In the case of high temperatures, higher values are permissible for expansion overall, i.e. the critical value for the permissible change with respect to the reference value increases with increasing operating temperature. Thus, for example, a change by 20%, based on the reference value, may already be caused solely by a customary operating temperature. However, if a change of 20% occurs in a "cold" state of the battery, this can already be an indication of a defective cell. Accordingly, a higher value is therefore set for the critical value as the operating temperature increases, from which the exceeding thereof predictively concludes that a fault has occurred.In an expedient embodiment, a respective sensor is designed as a differential capacitor with two opposite base electrodes and with a measuring electrode arranged therebetween. This embodiment enables a high sensitivity even in the case of very small distance changes.Expediently, the base electrodes and the measuring electrodes are designed as planar electrodes and are arranged parallel to one another.In an alternative embodiment, the base electrode and the measuring electrode are arranged in a Z-shape. Such a configuration of a Z-shaped differential capacitor is described, for example, in WO 2006 / 015565 A1.In an expedient embodiment, the base electrodes are at ground potential (ground) and the measuring electrode is connected to a measuring terminal of the evaluation unit. Generally, such a differential capacitor is formed by two capacitors connected in series. As a result, the capacitance and thus the sensitivity are increased overall. Due to the measure that the opposing, outer base electrodes are at ground potential, shielding by these base electrodes is achieved at the same time.The parallel arrangement of the electrodes described above is the preferred embodiment. This allows a particularly compact construction and even very small expansions of a cell and the resulting increase in pressure, which leads to minimal compression of the sensor, can therefore be detected reliably.The evaluation unit has in particular an oscillator, specifically an RC oscillator. Its resonant frequency shifts as a result of a change in capacitance of the capacitor formed by the sensor, so that accurate detection of a change is thus ensured.In a preferred embodiment, an elastic dielectric layer (made of a non-gaseous material) is arranged between the base electrode and the measuring electrode. This simultaneously defines an insulating spacer between the two electrodes and permits compression as a result of a thermally induced expansion of the cells.The dielectric layer preferably has a thickness in the range from 100 μm to 200 μm.By selecting the thickness and / or density of the dielectric layer, the properties of the capacitor (sensor) are influenced and can be adjusted as required.The electrodes, in particular the base electrodes, are formed by metal foils, in particular by copper foils. These have in particular a thickness in the range of only 50 to 80 μm.In a preferred embodiment, the evaluation unit is furthermore arranged within a module housing which surrounds the plurality of cells which are combined to form a cell module. This integral arrangement within the module housing achieves direct monitoring. The individual evaluation units of the respective cell modules of the battery are in particular connected to a central unit, for example a battery management system. This is also a central evaluation unit, which is typically arranged directly on the battery or integrated into the latter.Exemplary embodiments of the invention are explained in more detail below with reference to the figures. These are each shown in simplified representations. FIG. 1 shows a cell module with a plurality of cells integrated within a module housing with sensors arranged therebetween, FIG. 2 shows a battery with several of the cell modules shown in FIG. 1, FIG. 3 shows a measuring arrangement with a first variant of a capacitive sensor, and FIG. 4 shows a measuring arrangement with a second variant of a capacitive sensor.In the figures, parts with the same effect are represented by the same reference numerals.The cell module 2 shown in FIG. 1 has a module housing 4, within which a plurality of cells 6 are arranged. The cell module 2 extends in a transverse direction 8 and the individual cells, which are preferably approximately square-shaped, are arranged next to one another in this transverse direction 8. The module housing 4 has side walls 10, as viewed in the transverse direction 8, which clamp the cells 6 between them in the transverse direction.Viewed in the transverse direction 8, a sensor 12 is arranged in each case between two adjacent cells 6. This capacitor is designed in particular as a capacitive sensor and especially as a differential capacitor, as is described in more detail in different variants to FIGS. 3 and 4.The individual sensors 12 are therefore clamped between two adjacent cells 6. By the pressure exerted by the module housing 4, a pressure represented by first arrows 14 is exerted on the sensors 12.In the exemplary embodiment, a total of four cells 6 are shown. Each cell 6 has a housing 16. A respective sensor 12 is therefore arranged and clamped between walls of adjacent housings 16.The respective sensor 12 has a thickness of preferably 300 μm when viewed in the transverse direction 8. This thickness corresponds at the same time to a distance a between adjacent cells 6Within the respective module housing 4 there is furthermore arranged an evaluation unit 18, which is connected to each of the sensors 12 in order to record its measurement values. FIG. 1 schematically shows an evaluation circuit for the central sensor 12 which has an RC oscillator. The respective sensor 12 is connected to a measurement connection 20 of the evaluation unit 18 in each case. In the case of a change in the distance a, a change in the capacitance of the sensor is caused. Such a system changes the frequency of a periodic, for example sinusoidal, alternating voltage signal of the oscillator.In FIG. 1, the sensor 12 is designed as a differential capacitor with two opposing, flat base electrodes 22, a measuring electrode 24 arranged between them and a dielectric layer 26 arranged between two adjacent electrodes 22, 24, respectively.The base electrodes 22 are planar, foil-like elements which consist of metal, in particular copper. The two base electrodes 22 are at a common base or ground potential. In the exemplary embodiment, the two base electrodes 22 are formed integrally and are formed with one another by a transverse connecting piece 28, which is illustrated in a curved manner in the exemplary embodiment of FIG. 1. When viewed in cross section, the two base electrodes 22 therefore form a "U". The measuring electrode 24 arranged therebetween runs parallel to the two base electrodes 22 and extends along a planar plane perpendicular to the transverse direction 8 and can therefore be regarded as an "I" as seen in cross section. The illustrated sensor 12 is therefore also referred to as a "UI" sensor 12. The dielectric layers 26, like the base electrodes 22, are preferably integrally formed and have a cross-connection. They are therefore also U-shaped when viewed in cross section. Thus, base electrodes 22 and the electrical layers are stacked together as two U-shaped integral structures (as viewed in cross-section).As is shown in FIG. 2, in order to construct a battery 30, a plurality of such cell modules 2 are combined together within a battery housing 32 and are suitably interconnected with one another. The battery 30 has two connection poles 31 for connection, in particular, to a motor vehicle on-board power supply system. A central evaluation unit 34 is assigned to the battery 30, which is preferably arranged within the battery housing 32. This central evaluation unit 34 is in particular a so-called battery management system. This central evaluation unit 34 is in particular connected to the individual evaluation units 18. The individual module-specific evaluation units 18 together with the central evaluation unit 34 thus functionally form an evaluation unit which is designed for monitoring the battery, in particular with regard to premature detection of a thermal runaway.The individual sensors 12 together with the individual evaluation units 18 and optionally together with the central evaluation unit 34 form a measurement arrangement 36 which is designed for predictive detection of an undesired thermal runaway.A thermal runaway arises as a result of a malfunction within an individual cell 6, for example as a result of overload or as a result of an internal short circuit. This leads to thermal heating. If a limit temperature is reached, a chemical reaction occurs within the cell 6, which further heats the cell temperature. Such a reaction is enhanced by the increasing temperature. An impermissible temperature change is indicated by a thermally induced expansion of the cell 6.Such an expansion of a cell 6 leads to an increased pressure or to an expansion in the direction of the second arrows 38, as are shown in one of the cells 6 shown in FIG. 1. This (slight) expansion is detected by this cell 6, referred to below as defective cell 6a. The expansion of this defective cell 6a leads to a reduction of the distance a from the adjacent cells and thus to a compression of the sensors 12 which are present at this defective cell 6a. This compression leads to a change in capacitance, which is detected by the evaluation unit 18, 34.If this change in capacitance and thus the change in distance between two adjacent cells 6 exceeds a critical value, which indicates the potential occurrence of a thermal runaway, the evaluation unit 18, 34 emits a corresponding warning signal in order to initiate a countermeasure. This countermeasure consists, for example, in the disconnection of the battery or at least in a reduction in the load on the battery, for example a reduction in a charging current or a current currently output.The evaluation unit 18, 34 evaluates, in particular in parallel, the measurement results of the individual sensors 12 of a respective cell module 2. The evaluation unit 18, 34 detects here that the critical value is exceeded and initiates the countermeasure if the relative change (change in distance, change in capacitance) of the individual sensors 12 deviate from one another over a tolerance range. The tolerance range is, for example, + / -10%, + / -20% or + / -30%. This takes account of the fact that, in the case of a single defective cell 6 a, initially only this cell 6 aexpproportionally expands (in comparison to the non-defective cells 6) and therefore, in particular, the sensors 12 adjacent to this defective cell 6 aare subjected to excessive compression. Different changes are therefore an indication of the defective cell 6 a. Specifically, it is also localized because the sensors 12 adjacent to it show a disproportionate increase in capacitance.The evaluation unit 18, 34 is furthermore designed to take account of the temperature of the battery 30. For this purpose, at least one temperature sensor 40 is provided, which is shown in FIG. 2 by way of example as a component of the central evaluation unit 34. Alternatively, a temperature sensor 40 is arranged, for example, on or in each cell module 2 or each cell 6.The critical value from which a malfunction is concluded varies in this case as a function of the temperature detected by the temperature sensor 40. That is to say that the evaluation as to whether a defective cell 6 ais present generally takes place as a function of the detected current operating temperature of the battery 30 or at least of the current operating temperature of the respective cell module 2 or of the respective cell 6.Such a battery 30 is designed in particular as a high-voltage battery, specifically for the electrical supply of an electric drive motor (traction motor) of an electric or hybrid vehicle (motor vehicle), and is arranged in such a battery. The voltage of the battery 30 is typically in the range of several 100 volts.FIG. 3 shows in a greatly simplified manner a measuring arrangement 36 with the previously described UI sensor 12 (differential capacitor) with an evaluation unit 18 connected thereto. The two base electrodes 22 and the measuring electrode 24 are designed as flat electrodes and are arranged parallel to one another. The arrows shown illustrate the pressure exerted on the sensor 12. The two base electrodes 22 are connected to ground potential. The measuring electrode 24 is connected to an evaluation circuit. This evaluation circuit emits as an output signal a periodic alternating voltage signal, the period of which depends on the capacitance. When the sensor 12 is compressed, its capacitance increases, which leads to a change in the period.FIG. 4 shows an alternative embodiment of the capacitive sensor 12. In contrast to FIG. 3, the intermediate measuring electrode 24 is arranged not parallel but obliquely, so that the three electrodes are arranged approximately in a Z-shape when viewed in cross section. The base electrodes 22 are electrically decoupled from the measuring electrode 24. That is, the connection piece between the measuring electrode 24 and the two adjacent base electrodes 22 is formed by an electrical insulator.The variant of the UI sensor shown in FIG. 3 is the preferred embodiment, since it-viewed in the transverse direction 8-is of narrower construction and is therefore more suitable for the desired compact arrangement.The present invention is not limited to the described embodiment. Modifications are possible within the scope of the scope defined by the claims. In particular, instead of the capacitive sensors described here, other sensors, especially distance sensors, can also be used. The differential capacitors described here have, however, proved to be particularly suitable and sensitive.List of reference characters2 Cell module 4 Module housing 6 Cells 6 a Fehlerhafte cell 8 Transverse direction 10 Side walls 12 Sensor 14 First arrows 16 Housing 18 Evaluation unit 20 Measurement connection 22 Base electrodes 24 Measurement electrode 26 Dielectric layer 28 Transverse connecting piece 30 Battery 31 Connection pole 32 Battery housing 34 Central evaluation unit 36 Measurement arrangement 38 Second arrows d Thickness a Distance

Claims

Device for monitoring a battery (30), in particular a lithium-ion battery, in order to avoid thermal runaway, having the battery (30), which has a plurality of cells (6) which are arranged next to one another within a housing (16) under a prestress in a transverse direction (8), wherein a measuring arrangement (36) is provided for detecting an extent of at least one of the cells in the transverse direction (8) and the measuring arrangement (36) has a plurality of sensors (12) and an evaluation unit (18, 34), characterized in that the sensors (12) are each arranged between two cells (6) adjacent in the transverse direction (8) and are connected to the evaluation unit (18, 34), such that an extent of one of the cells (6) in the transverse direction (8) is detected by the measuring arrangement (36) and is monitored with regard to the exceeding of a critical value for the extent, wherein the critical value indicates a potential occurrence of a thermal runaway, characterized in that a detection unit (40) is provided for detecting a current operating temperature of the battery (30), and the evaluation unit (18, 34) is configured such that the critical value is set as a function of the current operating temperature.Device according to claim 1, in which a respective sensor (12) and the evaluation unit (18, 34) are designed to detect a change in distance between two cells (6) in the range between 1 μm and 50 μm.Device according to one of the preceding claims, in which the sensor (12) has a thickness (d) in the transverse direction (8) in the range from 150 μm to 500 μm and in particular in the range from 200 μm to 400 μm.Device according to one of the preceding claims, in which a sensor (12) is arranged in each case between each pair of cells (6).Device according to one of the preceding claims, in which the evaluation unit (18, 34) is designed to compare measured values of the sensors (12) with one another, wherein an uneven change in the measured values of the various sensors (12) is evaluated as exceeding the critical value.Device according to one of the preceding claims, in which a respective sensor (12) is designed as a differential capacitor having two opposite base electrodes (22) and having a measuring electrode (24) arranged therebetween.Device according to the preceding claim, in which the base electrodes (22) and the measuring electrode (24) are arranged parallel to one another.The device of claim 6, wherein the base electrodes (22) and the sensing electrode (24) are arranged in a Z-shape.Device according to one of Claims 6 to 8, in which the base electrodes (22) are at ground potential and the measuring electrode (24) is connected to a measurement connection (20) of the evaluation unit (18).Device according to one of Claims 6 to 9, in which an elastic dielectric layer (26) is arranged in each case between a base electrode (22) and the measuring electrode (24).Device according to the preceding claim, in which the dielectric layer (26) has a thickness in the range from 100 μm to 200 μmDevice according to one of the preceding claims, in which the cells (6) are combined to form a cell module (2) and are arranged within a module housing (4), wherein the evaluation unit (18) is arranged within the module housing (4).Method for monitoring a battery (30), in particular a lithium-ion battery (30), in order to avoid thermal runaway, wherein the battery (30) has a plurality of cells (6) which are arranged next to one another within a housing (16) under a bias voltage in a transverse direction (8), and an extent of at least one of the cells (6) in the transverse direction (8) is detected with the aid of a measuring arrangement (36), wherein a respective distance (a) between adjacent cells is monitored for this purpose, and wherein a countermeasure is initiated if a critical value for the extent, which indicates a potential occurrence of thermal runaway, is exceeded, characterized in that a current operating temperature of the battery (30) is detected and the critical value is set as a function of the current operating temperature.

Images