Method for detecting a cell fault state of a battery cell of a battery, detection device and motor vehicle

Abstract

The invention relates to a method for detecting a fault condition (F) of at least one first battery cell (16a) of a battery (18) having a plurality of battery cells (16), the cell voltage (Ul) of the first battery cell (16a) being determined repeatedly in an operating state (22, T) of the battery, in which operating state the change in the battery current (I) over time is less than a predefinable limit value, an electrical cell variable of the first battery cell being determined from the cell voltage of the first battery cell. The cell variable is then compared with a reference value (26a, 26b, U2), which is determined from the cell voltage detected at the respective point in time of the measurement of at least one battery cell different from the first battery cell, the fault condition (F) of the first battery cell being detected at least when the deviation (dl, d2) of the electrical cell variable (24a, 24b, Ul) from the first reference value provided at the same point in time of the measurement exceeds a predetermined first threshold value.

Description

Technical Field

[0001] This invention relates to a method for detecting the fault state of at least one first battery cell in a battery having multiple battery cells, wherein the cell voltage of the first battery cell is repeatedly / repeatedly determined at corresponding measurement times in at least one determined operating state of the battery, wherein the change of battery current over time is less than a preset limit, and an electrical cell parameter of the first battery cell is provided for the corresponding measurement time based on the repeatedly determined cell voltage of the first battery cell. The fault state can then be determined based on this electrical cell parameter. Furthermore, this invention also relates to a corresponding detection device for a motor vehicle and a motor vehicle having such a detection device. Background Technology

[0002] Following various instances of thermal runaway in one or more cells or batteries—such as laptop batteries—every effort has been made in recent years to prevent contamination during the lithium-ion cell manufacturing process. Experience has shown that it is desirable to supply all cells used in the automotive sector with sufficiently good quality lithium-ion batteries. However, in the current large-scale mass production of lithium-ion cells, it is impossible to completely eliminate particles or damage within the cells. All known quality assurance measures to date cannot guarantee 100% identification of cells with particles or other damage before delivery. However, such cells with particles can ultimately lead to battery fires and consequently vehicle fires. For example, such particles can cause damage to separators within the cell and may lead to micro-short circuits or even external short circuits. Accordingly, efforts are made to identify such fault conditions in battery cells as early as possible.

[0003] In this sense, DE 10 2014 204 956 A1 describes a method for identifying anomalies in a battery cell, wherein an event is detected in the signal of the battery cell's terminal voltage by a short-circuit sensor device, the event having successive edges at millisecond intervals, wherein the event detected by the short-circuit sensor device is transmitted to a battery management system, which determines the anomaly of the battery cell based on the detected event. Here, the short-circuit sensor device should particularly be configured to identify micro-short circuits, that is, to detect events having successive edges at intervals of several microseconds. Here, the amplitude of the terminal voltage fluctuates in the millivolt range. The internal current of this micro-short circuit causes a brief drop in the terminal voltage of several millivolts.

[0004] Aging effects can also cause changes in the voltage characteristics of individual cells. The methods described above can only insufficiently distinguish these changes from individual cell fault conditions, such as short circuits or micro-short circuits.

[0005] DE 10 2013 204 539 A1 describes a battery cell device having individual battery cells and a monitoring device for monitoring the battery cells. Here, the current or future state of the battery cells is identified or predicted based on current measurements of physical parameters. The battery state is identified or predicted using model-based analysis of the current measurements of the provided physical parameters. Furthermore, cell voltage, cell current, cell temperature, cell internal pressure, etc., can be detected as physical parameters.

[0006] Furthermore, EP 3 508 867 A1 describes a detection method for detecting micro-short circuits in a battery, wherein the leakage current of the battery is determined for detection. Specifically, this is determined by determining two reference charge capacities of the battery after charging and comparing these two reference charge capacities with each other. Here, the corresponding reference charge capacity is determined based on the difference between two electrical parameters, one representing the electrical parameters of the battery and the other representing the electrical parameters of a reference battery.

[0007] In addition, another drawback of the above method is that the possibility of detecting fault conditions is strongly limited in time, that is, limited to the quiescent phase or the phase after charging, in order to detect, for example, the quiescent voltage or leakage current of the battery or individual cell. Summary of the Invention

[0008] Therefore, the object of the present invention is to provide a method, a detection device, and a motor vehicle for detecting the fault state of a battery cell, which allows for the detection of the fault state of the battery cell as reliably and early as possible.

[0009] This objective is achieved by a method, a detection device, and a motor vehicle having the features according to the respective independent claims. Advantageous embodiments of the invention are the subject of the dependent claims, the description, and the drawings.

[0010] In the method according to the invention for detecting a fault state of at least one first battery cell in a battery having multiple battery cells, in at least one determined operating state of the battery, the cell voltage of the first battery cell is repeatedly determined at corresponding measurement times, wherein the change of battery current over time is less than a preset limit, and an electrical cell parameter of the first battery cell is provided for the corresponding measurement time based on the repeatedly determined cell voltage of the first battery cell. Furthermore, the electrical cell parameter of the first battery cell is compared with a corresponding first reference value for the measurement time, the first reference value being determined based on the cell voltage of at least one battery cell of the battery that is different from the first battery cell detected at the corresponding measurement time, wherein a fault state of the first battery cell is detected if at least one first precondition is met, namely, the deviation of the electrical cell parameter from the first reference value provided at the same measurement time exceeds a predetermined first threshold.

[0011] Therefore, the cell voltage of a single cell, i.e., the first battery cell, can be repeatedly measured, and the measured cell voltage or its associated cell parameter can be compared with a reference value, which in turn is related to the measured cell voltage of at least one other cell. Here, the cell voltages detected at each measurement moment can also be stored for evaluation and comparison at a later time. This invention is based on several understandings: on the one hand, it is possible to detect fault conditions, such as micro-short circuits, associated with specific changes in the cell voltage profile, for example, during charging, but also in other battery states. For example, during charging, the active material of the cell expands, and therefore the pressure in the cell increases near the end of the charging process, which may lead to an effect on the separator or minor damage. Such micro-short circuits do not usually cause cell runaway on their own, but they always damage the separator. For example, such micro-short circuits can therefore be identified in the charging voltage change profile, and a corresponding early response can be made. Therefore, this fault condition can be identified not only in the static state of a battery cell, i.e., when there is no charging current or discharge current flowing due to driving operation, but also in other operating states of the battery, i.e., as long as the change in battery current over time is less than a preset limit. A micro-short circuit can, for example, manifest as a temporary drop / disturbance in the cell voltage. This can be well identified not only in the static state of the battery but also, for example, during the charging process. Furthermore, a fault condition can also be identified if, for example, a particle, although not completely passing through the separator, damages the separator, allowing electrons to flow through the particle and the separator. This is not manifested as a short-term voltage change in the form of a voltage drop, but rather, for example, as a voltage change curve that becomes flatter at the end of the charging process. Generally, the present invention can advantageously identify fault conditions such as micro-short circuits, but it can also identify various defects or damages in the cell that are different from micro-short circuits. For example, damage to the insulation layer or the cell's zellbecher (cell housing) can also be identified earlier. Such damage can also lead to an external short circuit to another cell or bus, and is therefore very critical. However, this invention is primarily based on the understanding that by providing a first reference value based on the cell voltage of at least one other cell that differs from the observed first cell, the aging effect can also be considered, thereby better distinguishing the aging effect from the cell's fault state. The aging effect can also affect the voltage change curves of individual cells. However, because all cells within the battery are subjected to approximately the same aging conditions, such as load, temperature variations, etc., a comparison with other cells can significantly and better identify cell fault states that differ from pure aging effects, such as short circuits, micro-short circuits, or insulation damage. Therefore, this invention advantageously enables the detection of cell fault states in a significantly more reliable manner and, in significantly more cases, particularly earlier.

[0012] The battery is preferably a battery for motor vehicles, especially a power battery, which can be configured as a high-voltage battery, for example. Such a battery typically comprises multiple individual cells, which can also be combined into a battery module or battery pack. However, the battery can also simply be a battery module of such a high-voltage battery, comprising multiple such modules. Here, the individual cells can be provided as circular cells, pouch cells, or prismatic cells, or combinations thereof. The individual cells can be, for example, lithium-ion battery cells. Here, the variation of the battery current over time, below a preset limit, should especially include zero battery current. In other words, this operating state should also include the battery's resting state, in which the battery is unloaded and does not undergo charging or active discharging, for example, due to the battery's operation. However, the operating state can also be a state in which the battery current, i.e., the total battery current, is not zero, for example, during the charging process. Furthermore, another condition regarding the battery's operating state can be that variations in the battery current are only permitted within predetermined boundaries. In other words, the battery current is preferably constant, nearly constant, or at least exhibits only small fluctuations. Furthermore, each measurement moment can be a measurement time window of finite duration. The concept of measurement time here should only be used to illustrate that this measurement time window should be a very short period of time. Furthermore, it is preferable that the repetition rate of the individual cell voltage detection is as high as possible—this repetition rate can also be referred to as the sampling rate—so that the individual cell voltages can be measured quickly enough to detect events that occur only briefly, such as micro-short circuits. For example, this sampling rate can be at most a few milliseconds. In other words, it is preferable to repeatedly detect the individual cell voltage at time intervals of at most a few milliseconds. Therefore, the interval between two measurement times is preferably at most in the single-digit millisecond range.

[0013] Therefore, at the corresponding measurement moment, the cell parameters of the first battery cell can be provided, and the corresponding reference value and cell parameters can be compared with that reference value. If a deviation greater than a predetermined first threshold subsequently occurs, a fault condition can be inferred. However, it can be stipulated that other preconditions must be met before a fault condition can be considered detected. But at least at the time of measurement, a predetermined deviation of the cell parameters from the reference value exceeding the first threshold can also be the sole condition for detecting a fault condition. If a fault condition is detected, a corresponding warning can be issued to the driver of the motor vehicle, or alternatively or additionally, another measure can be initiated.

[0014] In an advantageous embodiment of the invention, a fault condition of the first battery cell is detected if, in addition to the first precondition, at least one second precondition is also met: the deviation of the change in the cell parameter over time from the change in the first reference value over time provided at the corresponding measurement moment exceeds a predetermined second threshold. The cell parameter can be, for example, the cell voltage itself. While the deviation of the cell voltage of the first battery cell from that of other battery cells can indicate a fault condition, it may also have other causes, such as a slight change in the capacity of the cell relative to other battery cells, which can very easily occur during the aging process of the battery cell. This correspondingly leads to a slight change in the charging profile. However, a fault condition of the battery cell, such as a short circuit or micro-short circuit, is strongly manifested by the sudden change in the cell voltage upon the occurrence of such an event, although in some cases it is only slight and / or short-lived. In other words, the deviation of the cell voltage of the first battery cell from that of the remaining battery cells is significantly stronger than usual. This can be advantageously detected by considering not only the cell parameter of the first battery cell but also its change over time. In other words, the voltage gradients of individual battery cells can be compared to detect the fault state of each cell. Therefore, fault states can be distinguished from other events much more easily and reliably. This reduces the number of false triggers caused by incorrectly assumed battery cell fault states and prevents unnecessary warnings from being issued to drivers.

[0015] Here, deviations between individual cell parameters and reference values, as well as deviations between changes in individual cell parameters over time and changes in reference values ​​over time, do not necessarily occur at the same measurement moment, but at least within the same, preferably short, observation period. Furthermore, when the cell voltage is detected at multiple successive measurement moments, especially over longer measurement periods, such as the duration of the charging process and / or the subsequent resting phase, this deviation can also be checked for. The subsequent evaluation allows for a simpler analysis of the cell parameters, particularly the cell voltage curve of the first cell over time.

[0016] In another advantageous embodiment of the invention, the individual parameter represents the individual voltage itself, and the first reference value represents a reference value for the individual voltage; and / or, the individual parameter represents the change of the individual voltage over time, and the first reference value represents the change of the reference value for the individual voltage over time; and / or, the individual parameter represents a higher / higher-order time derivative of the individual voltage (…). (zeitliche Ableitung) The first reference value represents the higher time derivative of the cell voltage reference value. In other words, the cell voltage itself can be considered a cell parameter, but alternatively or additionally, the higher time derivative of the cell voltage can also be considered a cell parameter. The reference value is always chosen as the corresponding parameter, that is, it is also chosen as the cell voltage reference value or the corresponding higher time derivative. It can also be specified here that the cell voltage is not considered at all, but only the higher time derivative, such as the first time derivative, the second time derivative, etc. As already mentioned, the fault state is particularly manifested in the gradient of the cell voltage of the defective cell involved, so it is particularly advantageous to perform such gradient observation.

[0017] In another advantageous embodiment of the invention, a first reference value is provided based on the individual cell voltages of all the battery cells together with the individual cell voltage of the first battery cell, particularly based on the average value of the individual cell voltages of all the battery cells. In other words, for example, if the cell parameter represents the individual cell voltage of the first battery cell, that individual cell voltage can be compared with the average value of all the battery cells. If the cell parameter is, for example, the change in individual cell voltage over time, it can be compared with the change in the average value of all the individual cell voltages over time, and so on. This allows for particularly reliable detection of abnormal behavior of a single cell relative to other cells. Even if a fault voltage is introduced when forming the average value, the average value will not decrease significantly due to the typically large number of battery cells in the battery, especially in the case of hundreds of battery cells. However, the battery can also be simply a battery module of a high-voltage battery. In this case, however, convincing information about the fault state of the battery cell can still be provided by comparing the individual cell voltage or a parameter derived therefrom with the corresponding average value. A significant advantage of considering the observed first battery cell when forming the average value is that the method is preferably implemented similarly for each battery cell. In other words, not only are the individual parameters of the first battery cell compared with this reference value to detect its fault condition, but the corresponding individual parameters of the second battery cell are also compared with the reference value, the individual parameters of the third battery cell are compared with the reference value, and so on. Therefore, the same reference value provided based on the described average value can be used for all battery cells. This greatly simplifies calculations during monitoring, thereby saving computation time and capacity. Therefore, it is not necessary to determine a specific reference value for each battery cell.

[0018] In another advantageous embodiment of the invention, a model-based second reference value is provided for the first battery cell at a corresponding measurement time, particularly independent of the detected cell voltages of other cells. A fault condition in the first battery cell is detected if the deviation of the cell parameter from the second reference value provided at the same measurement time exceeds a predetermined third threshold. In other words, not only can the cell parameter be compared with the corresponding cell parameters of other battery cells to detect fault conditions, such as the average cell voltage mentioned above, but it can also be compared with the model-based second reference value, which is independent of the cell voltages of the remaining battery cells. This cell-based model observation allows for more reliable detection of cell voltage variation curves that are outside the expected range. In particular, short-term and transient micro-short circuits, which manifest as short-term, transient voltage drops, can be reliably detected. This is especially true during the charging process, as the charging voltage curve of a battery cell typically extends very smoothly. Voltage drops can be detected accordingly simply, also independent of the observation of other cell voltages. In addition, considering another reference value as an additional precondition for detecting fault conditions makes fault condition detection more reliable and, in particular, more reliable in avoiding false triggering.

[0019] In another advantageous embodiment of the invention, at least one operating state is a charging state in which the battery is charged with a defined, and in particular, constant, charging current. As already described, this charging process has the significant advantage that large temporal variations in the battery current are typically not recorded. Charging is usually performed with a constant charging current for at least the majority of this charging process. The corresponding voltage curves of the individual battery cells are thus extended sufficiently smoothly, making it particularly easy to detect anomalies caused by faults.

[0020] Furthermore, the focus of monitoring can be placed at the end of the charging process. For example, this allows for more precise monitoring of individual cell parameters, as the probability of micro-short circuits increases due to the continuous expansion of the battery cells during charging.

[0021] In another advantageous embodiment of the invention, at least one operating state is a static state immediately following the charging process for charging the battery, which lasts for a maximum preset duration. This is based on the understanding that micro-short circuits also occur with increased probability shortly after the charging process for charging the battery is completed, for example, within five to ten minutes after the completion of the charging process. Therefore, it is particularly advantageous to monitor the battery for the occurrence of possible fault states within the time range immediately following this charging process—for example, within a maximum of 15 minutes. After the charging process, typically neither charging current nor discharging current flows, thus small voltage changes or anomalies in the individual cell voltage of the first battery cell can be detected particularly well and reliably within this range.

[0022] Nevertheless, it is also possible that at least one operating state represents a discharge state, provided that the conditions regarding battery current described at the beginning are met, i.e., the change of battery current over time is below a predetermined limit. Preferably, when the operating state is a discharge state, it is a state in which a discharge current is drawn from the battery—especially a constant one. For example, some batteries can be used for bidirectional charging. For example, a charged motor vehicle battery can be used to supply energy to other devices, especially those also outside the motor vehicle. This discharge current drawn from the battery is generally also constant, thus this is also a suitable operating state for the battery so that the fault condition of individual battery cells can be reliably detected based on this practice. This can also be a suitable operating state even if the motor vehicle is stopped, for example, at a red light, and therefore a discharge current of at least approximately constant is drawn from the battery used to power the motor vehicle's electrical consumers during that phase.

[0023] In particular, monitoring according to the method can also be performed in all of these suitable operating conditions. This enables comprehensive monitoring of the battery regarding the occurrence of fault states, which in turn enables very early detection of fault states and timely activation of warning measures or other countermeasures.

[0024] Furthermore, the present invention relates to a detection device for detecting a fault state of at least one first battery cell in a battery having multiple battery cells, wherein the detection device is designed to repeatedly determine the cell voltage of the first battery cell at corresponding measurement times in at least one determined operating state of the battery, wherein the change of battery current over time is less than a preset limit, and to provide an electrical cell parameter of the first battery cell based on the repeatedly determined cell voltage of the first battery cell for the corresponding measurement time. Furthermore, the detection device is designed to determine a first reference value based on the cell voltage of at least one battery cell of the battery that is different from the first battery cell detected at the corresponding measurement time, compare the electrical cell parameter of the first battery cell with the corresponding first reference value for the measurement time, and detect a fault state of the first battery cell if at least one first precondition is met, namely, the deviation of the electrical cell parameter from the first reference value provided at the same measurement time exceeds a predetermined first threshold.

[0025] The advantages described in the method and its embodiments according to the invention are applied in the same manner to the detection device according to the invention.

[0026] Furthermore, the present invention also relates to a motor vehicle having a detection device according to the present invention or one of its design schemes.

[0027] Improvements to the detection device according to the present invention also belong to the present invention, and these improvements have the features already described in conjunction with the improvements according to the method according to the present invention. For this reason, corresponding improvements to the detection device according to the present invention will not be described here.

[0028] The motor vehicle according to the invention is preferably designed as an automobile, especially a passenger car or a truck, or as a sedan or a motorcycle.

[0029] The present invention also includes combinations of features of the described embodiments. Therefore, the present invention also includes implementations that, unless described as mutually exclusive, each have a combination of features of multiple embodiments in the described embodiments. Attached Figure Description

[0030] Embodiments of the present invention are described below. For this purpose, it is shown that:

[0031] Figure 1 A schematic diagram of a motor vehicle according to an embodiment of the present invention is shown, the motor vehicle having a detection device for detecting the fault status of individual battery cells of the motor vehicle battery;

[0032] Figure 2A graph showing a comparison between the cell voltage variation curve of a battery cell according to an embodiment of the present invention and a reference voltage used to detect the fault state of the battery cell; and

[0033] Figure 3 A diagram showing a comparison between the cell voltage variation curve of a battery cell during charging and a reference voltage used to detect the fault state of the battery cell, according to another embodiment of the present invention. Detailed Implementation

[0034] The embodiments described below are preferred embodiments of the present invention. In the embodiments, the described parts are various features of the present invention that can be considered independently of each other, and these features also independently improve the present invention. Therefore, this disclosure is intended to include combinations of features of the embodiments other than those shown. Furthermore, the embodiments may also be supplemented by other features of the present invention already described.

[0035] In the accompanying drawings, the same reference numerals denote elements that have the same function.

[0036] Figure 1 A schematic diagram of a motor vehicle 10 according to an embodiment of the present invention is shown, the motor vehicle having a detection device 12 for detecting a fault condition F of a battery cell 16 of a battery 18 of the motor vehicle. Here, the battery 18 may be configured as a high-voltage battery of the motor vehicle 10 or as a battery module of such a high-voltage battery. Here, the battery 18 also includes a plurality of battery cells 16. One of these battery cells 16 is hereby additionally indicated by reference numeral 16a in order to better illustrate and describe the method for detecting the fault condition F of such battery cell 16. Accordingly, the method for detecting the fault condition of such battery cell 16 is explained by means of this first battery cell 16a, but can also be applied in the same manner to all the remaining battery cells 16. If the fault condition F of such battery cell 16 is detected by the detection device 12, a signal S can be output, such as a warning signal to the driver of the motor vehicle or a signal for taking specific measures, such as shutting off the battery, battery cell, etc.

[0037] Impurities and particles in these cells can damage the separator, ultimately leading to battery fire and vehicle fire. Because the active material in the cell expands during charging, causing an increase in pressure within the cell, this can potentially affect or slightly damage the separator towards the end of the charging process. These micro-short circuits do not usually cause cell 16 to run away on their own, but they always damage the separator. However, these micro-short circuits can be identified in the charging voltage variation curve and responded to accordingly, such as by outputting the signal S described above.

[0038] This allows for the advantageous identification of particles that continue to pass through the separator from one charging cycle to another. This may impede charging and can notify the user, allowing cell 16a or battery 18 to be replaced before a fire occurs.

[0039] Here, as assumed in monomer 16a, after the pressure in monomer 16a reaches its peak due to the expansion of the active material at the end of charging, the likelihood of particles damaging monomer 16a, such as separators, monomer cup-shaped shells, etc., is also highest. This damage typically leads to micro-short circuits, which, although not yet causing runaway of monomer 16a, can preemptively damage the separators of monomer 16a, potentially causing them to fail during subsequent operation.

[0040] At the same time, the current change curve, and consequently the voltage change curve during AC or DC charging, is very smooth and uniform, making it easy to quickly and easily identify outliers.

[0041] For particles that have passed through a separator or a single-celled cup-shaped casing but have not yet caused a complete short circuit, the following is typical: Figure 2 and Figure 3 The voltage change curves of each individual cell shown, such as the voltage change curve of cell 16a, can be detected as described below.

[0042] Figure 2 An exemplary illustration is shown of such a current variation curve 20 of the charging current I during the charging process 22 for charging battery cell 16a and the remaining battery cells 16. Here, similar to the voltage variation curve 24a of battery cell 16a, the current variation curve 20 is shown according to the current state of charge (SOC) of the battery 18, which can also be understood as a current variation curve of the battery current. The voltage curve 24a therefore represents the individual cell voltage U1 of battery cell 16a, particularly its variation over time, or as shown in... Figure 2 The curve depicting the change in the state of charge (SOC) of battery 18 is shown below. Furthermore, in... Figure 2 The diagram also shows a reference voltage curve 26a, which in this example illustrates the variation of the reference voltage U2 with respect to the state of charge (SOC) over time. This reference voltage U2 can be provided, for example, as the average cell voltage across all the individual cells 16 of the battery 18. Alternatively or additionally, a model-based voltage variation curve can also be used as a reference.

[0043] To detect fault condition F, it is advantageous to measure the individual cell voltages, such as the cell voltage U1 of the first battery cell 16a here, quickly enough, for example at intervals of only a few milliseconds, and then evaluate the voltage change curve 24a.

[0044] exist Figure 2 In the first case shown, the particle penetrates the separator, and due to the resulting micro-short circuit, the voltage U1 of the cell 16a containing the particle drops briefly, that is, within milliseconds. This voltage drop occurs in... Figure 2 This is indicated by reference numeral 28 in the attached figure. Therefore, the short circuit disappears without consequence, and the cell resumes normal operation. In this case, a brief voltage drop 28 in cell 16a at the end of charging can be detected.

[0045] As in Figure 2 As can be seen, this detection can be performed simply by comparing voltage curve 24a with reference curve 26a at various measurement times. If the comparison has, for example, a deviation greater than a predetermined limit, indicated by reference numeral d1 in the attached figure, it can be evaluated as an indication of a fault state in cell 16a. Furthermore, it is advantageous to evaluate not only the voltage curves 24a and 26a by comparison with each other, but also, for example, their temporal gradient. This allows for a significantly more effective exclusion of effects caused by aging. Figure 2 As can be seen, this voltage drop 28 indicates a short-term and sudden voltage change. Accordingly, it is advantageous to compare the time gradients of the individual cell voltages 16 with each other or with an average value U2, which is formed based on all the individual voltages of the cell 16.

[0046] Figure 3 Similar to Figure 2 Another possible voltage change curve 24b for battery cell 16a is shown, which is also plotted here with respect to the state of charge (SOC). Voltage change curve 24b also relates to the charging process 22. The charging current I is also shown again, which is... Figure 2 The charging current is designed in the same way. This charging current I corresponds to the battery current during the charging process 22. In addition to the voltage curve 24b of the battery cell 16a, a reference voltage curve 26b is also shown here, which can also be provided based on the average value of the individual cell voltages of all battery cells 16.

[0047] In this example, the particle does not completely penetrate the separator of monomer 16a, but damages the separator, allowing electrons to flow through the particle and the separator. This is also known as a soft short circuit. This is manifested in that the voltage of monomer 16a typically begins to level off or even decrease again shortly before the end of charging, compared to all other monomers 16, because monomer 16a discharges through its own particles. Accordingly, this can be detected by the voltage change curve 24b at the end of charging. Thus, it is detected when the voltages of all monomers 16 are close to each other for a long time during charging, and monomer 16a only suddenly transitions to—here indicated by reference numeral 30—a flatter voltage change curve until the end of charging, or, in extreme cases, the monomer voltage decreases again even during charging. The period shortly before the end of charging... Figure 3 This is also indicated by reference numeral 32 in the accompanying drawings. This phenomenon will not occur, for example, in cells 16 that only have different capacities. In other words, the difference between cells with only different capacities and this reference voltage curve 26b in terms of their voltage change curves is that the voltage curve of this cell gradually deviates throughout the charging process 22, but not specifically within the end range 32 of the charging process 22, and not so abruptly. Accordingly, this fault condition can also be detected here by, for example, selecting a limit for this deviation d2. If the voltage curve 24a has a defined interval from the reference curve 26b, and this interval exceeds the threshold, then this again indicates a fault. Additional conditions can also be set here, for example, on the gradient of the voltage change curve 24b, and / or, for example, such that this deviation d2 only occurs within a defined range of the charging voltage curve 24b, but not throughout the entire charging curve and / or especially only within the range of the end of charging 32.

[0048] Here, in response to Figure 2 and Figure 3 Combinations of the two scenarios described are also possible.

[0049] Furthermore, it is also possible that this single-cell defect occurs only after charging process 22. Therefore, it is equally advantageous, for example, to observe the single-cell voltage U1 within a defined time range T, which immediately follows charging process 22. This time range T also includes... Figure 2 and Figure 3 As illustrated in the example. The defect may also occur within this time frame T, and for example, a short, sudden voltage drop may occur, such as in... Figure 2 As described in, or as in Figure 3As described, the decrease in the individual cell voltage U1 may occur within the indicated time range T only after this charging process 22. This can then be detected by appropriate measures, in particular by comparing the individual cell voltage curves 24a, 24b with the corresponding reference curves 26a, 26b, and especially by additionally considering the time gradient.

[0050] In summary, these embodiments demonstrate how impurity particles in lithium monomers can be detected early in a reliable and simple manner during charging and in other operating states.

Claims

1. A method for detecting the fault state of at least one first battery cell (16a) of a battery (18) having a plurality of battery cells (16), wherein, In at least one defined operating state of the battery (18), the cell voltage (U1) of the first battery cell (16a) is repeatedly determined at the corresponding measurement time. In the at least one defined operating state, the change of battery current over time is less than a preset limit. For the corresponding measurement time, the electrical cell parameter of the first battery cell (16a) is provided based on the repeatedly determined cell voltage (U1) of the first battery cell (16a). Its features are, The electrical parameters of the first battery cell (16a) are compared with a corresponding first reference value at a measurement time. This first reference value is determined based on the cell voltage of at least one other battery cell in the battery (18) that is different from the first battery cell (16a) detected at the corresponding measurement time, in order to distinguish the aging effects of all battery cells from the fault state of the first battery cell. A fault state of the first battery cell (16a) is detected if at least one first precondition is met, namely, the deviation of the electrical parameters from the first reference value provided at the same measurement time exceeds a predetermined first threshold. Among them, at least one operating state is a charging state. If, in addition to the first precondition, at least one second precondition is also met, namely, the deviation between the change of the electrical single cell parameter over time and the change of the first reference value provided at the corresponding measurement time over time exceeds a predetermined second threshold, and such deviation only occurs within a certain range of the charging voltage curve but not on the entire charging curve, then a fault state of the first battery cell (16a) is detected.

2. The method according to claim 1, Its features are, The individual parameter represents the individual voltage itself, and the first reference value represents the individual voltage reference value; and / or, the individual parameter represents the change of the individual voltage over time, and the first reference value represents the change of the individual voltage reference value over time; and / or, the individual parameter represents the higher time derivative of the individual voltage, and the first reference value represents the higher time derivative of the individual voltage reference value.

3. The method according to claim 1 or 2, Its features are, A first reference value is provided based on the individual cell voltages of all the individual cells (16) of the battery (18) together with the individual cell voltage of the first individual cell (16a).

4. The method according to claim 3, characterized in that, A first reference value is provided based on the average value of the individual cell voltages of all battery cells (16).

5. The method according to claim 1 or 2, Its features are, For the corresponding measurement time, a model-based second reference value is provided for the first battery cell (16a), wherein if the following third precondition is met, namely, the deviation of the electrical cell parameter from the second reference value provided at the same measurement time exceeds a predetermined third threshold, then a fault state of the first battery cell (16a) is detected.

6. The method according to claim 1 or 2, Its features are, In the charging state, the battery (18) is charged with a defined charging current.

7. The method according to claim 1 or 2, Its features are, At least one operating state is a static state that immediately follows the charging process for charging the battery (18).

8. The method according to claim 7, Its features are, The static state can last for a maximum preset duration.

9. The method according to claim 1 or 2, Its features are, At least one operating state is a discharge state, in which discharge current is drawn from the battery (18).

10. A detection device (12) for detecting the fault state of at least one first battery cell (16a) of a battery (18) having multiple battery cells (16), wherein, The detection device (12) is designed to repeatedly determine the cell voltage of the first battery cell (16a) at corresponding measurement times in at least one determined operating state of the battery (18), wherein the change of battery current over time is less than a preset limit, and to provide the electrical cell parameters of the first battery cell (16a) based on the repeatedly determined cell voltage of the first battery cell (16a) at the corresponding measurement times. Its features are, The detection device (12) is designed to determine a first reference value based on the cell voltage of at least one cell of the battery (18) that is different from the first battery cell (16a) detected at a corresponding measurement time, in order to distinguish the aging effects of all battery cells from the fault state of the first battery cell. The device compares the electrical cell parameters of the first battery cell (16a) with the corresponding first reference value at the measurement time. If at least one first precondition is met—that is, the deviation of the electrical cell parameters from the first reference value provided at the same measurement time exceeds a predetermined first threshold—then a fault state of the first battery cell (16a) is detected. Among them, at least one operating state is a charging state. If, in addition to the first precondition, at least one second precondition is also met, namely, the deviation between the change of the electrical single cell parameter over time and the change of the first reference value provided at the corresponding measurement time over time exceeds a predetermined second threshold, and such deviation only occurs within a certain range of the charging voltage curve but not on the entire charging curve, then a fault state of the first battery cell (16a) is detected.

11. A motor vehicle (10) having a detection device (12) according to claim 10.

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