A method and related device for monitoring thermal runaway of battery cells

Abstract

This application discloses a method and related apparatus for monitoring thermal runaway of battery cells. To monitor the state of battery cells in a battery pack and determine whether thermal runaway has occurred, an alternating current signal is injected into the high voltage of the battery pack. The internal resistance of each of the multiple battery cells in the battery pack is monitored to obtain the rate of change of internal resistance for each cell. If the rate of change of internal resistance of a certain cell, such as the first cell, exceeds a first threshold, and the difference between the rate of change of internal resistance of the first cell and the rate of change of internal resistance of other cells, such as the second cell, is greater than a second threshold, it indicates that the internal chemical structure of the first cell may have changed, possibly due to thermal runaway. Therefore, thermal runaway of the first cell is confirmed. This method can effectively detect the internal resistance of the battery cells and use impedance data for thermal runaway monitoring. It can effectively monitor the state of the battery cells, accurately determine whether thermal runaway has occurred, minimize missed or false detections, and reduce the direct and secondary damage caused by thermal runaway.

Description

Technical Field

[0001] This invention relates to the automotive field, and more particularly to a method and related apparatus for monitoring thermal runaway of battery cells. Background Technology

[0002] With the development of new energy vehicles, the requirements for battery packs and battery management systems are becoming increasingly stringent, especially regarding the safety capabilities of power batteries. In power battery systems, thermal runaway transmission within cells is the most typical internal cause of spontaneous combustion in battery packs. To improve the safety performance of battery packs, it is necessary to monitor and provide early warning of cell thermal runaway.

[0003] Currently, monitoring of thermal runaway in battery cells mainly involves monitoring the cell voltage. If the cell voltage drops by more than 25% of the initial voltage, or if the temperature at the monitored point reaches its maximum operating temperature, or if the monitored temperature reaches its maximum operating temperature and the temperature rise rate at the monitored point is ≥1℃ / s and lasts for more than 3 seconds, then thermal runaway in the cell is considered to have occurred. However, this monitoring method is prone to missed or false detections. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a method and related apparatus for monitoring thermal runaway of battery cells. This method can effectively detect the internal resistance of the battery cell and use impedance data for thermal runaway monitoring. It can effectively monitor the battery cell status, accurately determine whether thermal runaway has occurred, and minimize missed or false detections. This allows for early warning before thermal runaway occurs, reducing direct and secondary damage caused by thermal runaway.

[0005] The embodiments of this application disclose the following technical solutions:

[0006] In a first aspect, embodiments of this application provide a method for monitoring thermal runaway of a battery cell, the method comprising:

[0007] An alternating current signal is injected into the high voltage of the battery pack, which includes multiple battery modules, each of which includes multiple battery cells;

[0008] The internal resistance of each cell in the battery pack is monitored to obtain the rate of change of internal resistance of each cell.

[0009] If the rate of change of internal resistance of the first cell in the plurality of cells exceeds a first threshold, and the difference between the rate of change of internal resistance of the first cell and the rate of change of internal resistance of the second cell is greater than a second threshold, it is determined that the first cell has thermal runaway; the second cell is any other cell in the battery pack besides the first cell.

[0010] In one possible implementation, the method further includes:

[0011] If the rate of change of internal resistance of the first battery cell exceeds a first threshold, and the duration for which the difference between the rate of change of internal resistance of the first battery cell and the rate of change of internal resistance of the second battery cell is greater than a second threshold reaches a third threshold, a thermal runaway warning is issued for the first battery cell.

[0012] In one possible implementation, the injection of an AC current signal into the high voltage of the battery pack includes:

[0013] Detect the vehicle's current.

[0014] If the vehicle current is less than or equal to the fourth threshold, the AC current signal is injected into the high voltage of the battery pack.

[0015] In one possible implementation, monitoring the internal resistance of each of the multiple cells in the battery pack to obtain the rate of change of internal resistance of each cell includes:

[0016] Detect the internal resistance of each cell at different times;

[0017] For each cell, the rate of change of the cell's internal resistance is calculated based on the cell's internal resistance at different times.

[0018] In one possible implementation, taking any one of the different times as the target time, and each battery cell as a target battery cell, the method for detecting the internal resistance of the target battery cell at the target time includes:

[0019] By monitoring the AC current signals at both ends of the target cell, the phase difference between the sampled signal and the injected signal at the target time is obtained:

[0020] The internal resistance of the target cell at the target time is calculated based on the phase difference.

[0021] In one possible implementation, calculating the internal resistance of the target cell based on the phase difference includes:

[0022] Extract the signal component of the target frequency from the sampled signal, wherein the target frequency is the frequency of the alternating current signal;

[0023] The internal resistance of the target cell at the target time is obtained by calculating the magnitude and phase difference based on the signal components.

[0024] Secondly, embodiments of this application provide a monitoring device for thermal runaway of battery cells, the device comprising:

[0025] An injection unit is used to inject an AC current signal into the high voltage of the battery pack, wherein the battery pack includes multiple battery modules, and each battery module includes multiple cells;

[0026] The monitoring unit is used to monitor the internal resistance of each of the multiple cells in the battery pack and obtain the rate of change of internal resistance of each cell.

[0027] The determining unit is configured to determine that the first battery cell has experienced thermal runaway if the rate of change of internal resistance of the first battery cell among the plurality of battery cells exceeds a first threshold and the difference between the rate of change of internal resistance of the first battery cell and the rate of change of internal resistance of the second battery cell is greater than a second threshold; the second battery cell refers to the other battery cells in the battery pack besides the first battery cell.

[0028] In one possible implementation, the device further includes:

[0029] The early warning unit is used to issue a thermal runaway early warning for the first battery cell if the rate of change of internal resistance of the first battery cell exceeds a first threshold and the duration of the difference between the rate of change of internal resistance of the first battery cell and the rate of change of internal resistance of the second battery cell being greater than a second threshold reaches a third threshold.

[0030] In one possible implementation, the injection unit is used for:

[0031] Detect the vehicle's overall current.

[0032] If the vehicle current is less than or equal to the fourth threshold, the AC current signal is injected into the high voltage of the battery pack.

[0033] In one possible implementation, the monitoring unit is used for:

[0034] Detect the internal resistance of each cell at different times;

[0035] For each cell, the rate of change of the cell's internal resistance is calculated based on the cell's internal resistance at different times.

[0036] In one possible implementation, any one of the different times is taken as the target time, and each battery cell is taken as the target battery cell. The monitoring unit is used for:

[0037] By monitoring the AC current signals at both ends of the target cell, the phase difference between the sampled signal and the injected signal at the target time is obtained:

[0038] The internal resistance of the target cell at the target time is calculated based on the phase difference.

[0039] In one possible implementation, the monitoring unit is used for:

[0040] Extract the signal component of the target frequency from the sampled signal, wherein the target frequency is the frequency of the alternating current signal;

[0041] The internal resistance of the target cell at the target time is obtained by calculating the magnitude and phase difference based on the signal components.

[0042] As can be seen from the above technical solution, the battery packs used in modern vehicles include multiple battery modules, and each battery module includes multiple cells. To monitor the state of the cells in the battery pack and determine whether thermal runaway has occurred, an AC current signal can be injected into the high voltage of the battery pack. Then, the internal resistance of each cell in the battery pack is monitored to obtain the rate of change of internal resistance of each cell. If the rate of change of internal resistance of a cell, such as the first cell, exceeds a first threshold, and the difference between the rate of change of internal resistance of the first cell and the rate of change of internal resistance of other cells, such as the second cell, is greater than a second threshold, it indicates that the internal chemical structure of the first cell may have changed. This change may be due to thermal runaway, and it can be determined that the first cell has experienced thermal runaway. This method can effectively detect the internal resistance of the cells and use impedance data for thermal runaway monitoring. It can effectively monitor the state of the cells, accurately determine whether thermal runaway has occurred, and minimize missed or false detections, so as to provide early warning before thermal runaway and reduce the direct and secondary damage caused by thermal runaway. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 A flowchart illustrating a method for monitoring thermal runaway of a battery cell, provided in an embodiment of this application;

[0045] Figure 2 This is a schematic diagram of a cell internal resistance detection method provided in an embodiment of this application;

[0046] Figure 3 A flowchart illustrating a method for monitoring thermal runaway of a battery cell, provided in an embodiment of this application;

[0047] Figure 4 This is a structural diagram of a battery cell thermal runaway monitoring device provided in an embodiment of this application. Detailed Implementation

[0048] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0049] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0050] Currently, monitoring of thermal runaway in battery cells mainly involves monitoring the cell voltage. If the cell voltage drops by more than 25% of the initial voltage, or if the temperature at the monitored point reaches its maximum operating temperature, or if the monitored temperature reaches its maximum operating temperature and the temperature rise rate at the monitored point is ≥1℃ / s and lasts for more than 3 seconds, then thermal runaway in the cell is considered to have occurred. However, this monitoring method is prone to missed or false detections.

[0051] To address the aforementioned technical problems, this application provides a method for monitoring thermal runaway of battery cells. This method injects an alternating current signal into the high voltage of a battery pack. Then, the internal resistance of each of the multiple battery cells in the battery pack is monitored to obtain the rate of change of internal resistance for each cell. If the rate of change of internal resistance of a cell, such as the first cell, exceeds a first threshold, and the difference between the rate of change of internal resistance of the first cell and the rates of change of internal resistance of other cells, such as the second cell, is greater than a second threshold, it indicates that the internal chemical structure of the first cell may have changed. This change may be due to thermal runaway, thus confirming that the first cell has experienced thermal runaway. This method can effectively detect the internal resistance of the battery cells and use impedance data for thermal runaway monitoring. It can effectively monitor the cell status, accurately determine whether a cell has experienced thermal runaway, and minimize missed or false detections. This allows for early warning before thermal runaway, reducing the direct and secondary damage caused by thermal runaway.

[0052] For ease of understanding, the monitoring method for thermal runaway of battery cells provided in the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0053] See Figure 1 , Figure 1 A method for monitoring thermal runaway in battery cells is shown, the method comprising:

[0054] S101, Inject AC current signal into the high voltage of the battery pack.

[0055] Modern vehicles use battery packs containing multiple battery modules, each containing multiple battery cells. When a battery cell experiences thermal runaway, regardless of the triggering cause (primarily electrical, mechanical, or thermal), the cell's internal chemical structure undergoes corresponding changes. These changes result in a significant change in the cell's internal resistance within a short period (a sudden increase or decrease). Therefore, in this embodiment, the change in the cell's internal resistance can be used to accurately determine whether a cell has experienced thermal runaway.

[0056] In this embodiment, the battery cell thermal runaway can be monitored using the vehicle's Battery Management System (BMS). To monitor the state of the cells in the battery pack and determine whether thermal runaway has occurred, an AC current signal can be injected into the high voltage of the battery pack to monitor changes in the cell's internal resistance.

[0057] It should be noted that in one possible implementation, injecting an AC current signal into the high voltage of the battery pack requires certain conditions to be met. Therefore, the way to inject an AC current signal into the high voltage of the battery pack is to first detect the vehicle current. If the vehicle current is less than or equal to a certain threshold, such as the fourth threshold I, then inject an AC current signal into the high voltage of the battery pack. Otherwise, there is no need to execute S101, and continue to detect the vehicle current.

[0058] S102. Monitor the internal resistance of each cell in the battery pack to obtain the rate of change of internal resistance of each cell.

[0059] In one possible implementation, the internal resistance of each of the multiple cells in the battery pack is monitored. The rate of change of internal resistance for each cell can be obtained by detecting the internal resistance of each cell at different times, and then calculating the rate of change of internal resistance for each cell based on its internal resistance at different times. The rate of change of internal resistance can be the change in internal resistance per unit time.

[0060] For example, for a target battery cell, the internal resistance of the target battery cell is monitored in real time. If the internal resistance of the target battery cell is detected at time t1 and time t2, the change value of the internal resistance from time t1 to time t2 and the time interval from time t1 to time t2 are calculated. Then, the rate of change of the internal resistance of the target battery cell is calculated based on the change value of the internal resistance and the time interval.

[0061] Next, any time from different times is taken as the target time, and each cell is taken as the target cell. In this embodiment, the method for detecting the internal resistance of the target cell at the target time can be to monitor the AC current signal at both ends of the target cell to obtain the phase difference between the sampled signal and the injected signal at the target time, and then calculate the internal resistance of the target cell at the target time based on the phase difference.

[0062] Specifically, the method for calculating the internal resistance of the target cell based on the phase difference can be to extract the signal component of the target frequency from the sampled signal, where the target frequency is the frequency of the AC current signal; and to obtain the internal resistance of the target cell at the target time based on the magnitude and phase difference calculated from the signal component.

[0063] See Figure 2 As shown, Figure 2 This is a schematic diagram of a cell internal resistance detection method provided in an embodiment of this application. It includes module 1, module 2, ..., module n, a main positive relay, and a main negative relay. A controlled alternating current signal is injected into the high-voltage terminal of the battery pack, and then continuous voltage signal sampling is performed to obtain a sampled signal. The sampled signal is then subjected to a Fast Fourier Transform (FFT) algorithm to extract the signal component with the target frequency f0 (the frequency of the injected alternating current signal) to reduce the influence of other signals. Then, the modulus |Z| and phase difference are calculated based on the corresponding signal components. The internal resistance of the target battery cell at the target time is obtained. For example, it can be determined based on... The corresponding internal resistance is obtained.

[0064] S103. If the rate of change of internal resistance of the first cell in the plurality of cells exceeds a first threshold, and the difference between the rate of change of internal resistance of the first cell and the rate of change of internal resistance of the second cell is greater than a second threshold, it is determined that the first cell has thermal runaway; the second cell is any other cell in the battery pack besides the first cell.

[0065] If the rate of change of internal resistance of the first cell exceeds the first threshold Δr1, then the rate of change of internal resistance of the first cell is compared with the rate of change of internal resistance of other cells in the entire battery pack. If the difference between the rate of change of internal resistance of the first cell and the rate of change of internal resistance of other cells is greater than the second threshold Δr2, then it can be determined that the first cell has experienced thermal runaway, and the first cell can be marked.

[0066] In some cases, if the rate of change of internal resistance of the first cell in a plurality of cells exceeds a first threshold, and the duration for which the difference between the rate of change of internal resistance of the first cell and the rate of change of internal resistance of the second cell is greater than a second threshold reaches a third threshold Δt1, then a thermal runaway warning is issued for the first cell, for example, a thermal runaway warning is output, in order to achieve the goal of BMS safety monitoring.

[0067] As can be seen from the above technical solution, the battery packs used in modern vehicles include multiple battery modules, and each battery module includes multiple cells. To monitor the state of the cells in the battery pack and determine whether thermal runaway has occurred, an AC current signal can be injected into the high voltage of the battery pack. Then, the internal resistance of each cell in the battery pack is monitored to obtain the rate of change of internal resistance of each cell. If the rate of change of internal resistance of a cell, such as the first cell, exceeds a first threshold, and the difference between the rate of change of internal resistance of the first cell and the rate of change of internal resistance of other cells, such as the second cell, is greater than a second threshold, it indicates that the internal chemical structure of the first cell may have changed. This change may be due to thermal runaway, and it can be determined that the first cell has experienced thermal runaway. This method can effectively detect the internal resistance of the cells and use impedance data for thermal runaway monitoring. It can effectively monitor the state of the cells, accurately determine whether thermal runaway has occurred, and minimize missed or false detections, so as to provide early warning before thermal runaway and reduce the direct and secondary damage caused by thermal runaway.

[0068] The following describes a method for monitoring thermal runaway of battery cells provided in this application, using a practical application scenario. (See also...) Figure 3 The method includes:

[0069] S301. Detect whether the vehicle current is less than or equal to the fourth threshold. If so, proceed to S302.

[0070] S302, Inject AC current signal into the high voltage of the battery pack.

[0071] S303. Monitor the internal resistance of each cell in the battery pack to obtain the rate of change of internal resistance of each cell.

[0072] S304. Determine whether the rate of change of the internal resistance of the first cell exceeds the first threshold. If yes, execute S305; otherwise, execute S301.

[0073] S305. Determine whether the difference between the rate of change of internal resistance of the first cell and the rate of change of internal resistance of the second cell is greater than the second threshold. If yes, execute S306; otherwise, execute S301.

[0074] S306. Determine whether the duration has reached the third threshold. If yes, execute S307; otherwise, execute S301.

[0075] S307, output thermal runaway warning.

[0076] based on Figure 1 A corresponding embodiment provides a method for monitoring thermal runaway of a battery cell; this application embodiment provides a device for monitoring thermal runaway of a battery cell. See also... Figure 4 The device includes:

[0077] The injection unit 401 is used to inject an AC current signal into the high voltage of the battery pack, wherein the battery pack includes multiple battery modules, and each battery module includes multiple cells.

[0078] The monitoring unit 402 is used to monitor the internal resistance of each of the multiple cells in the battery pack and obtain the rate of change of the internal resistance of each cell.

[0079] The determining unit 403 is configured to determine that the first battery cell has thermal runaway if the rate of change of internal resistance of the first battery cell among the plurality of battery cells exceeds a first threshold and the difference between the rate of change of internal resistance of the first battery cell and the rate of change of internal resistance of the second battery cell is greater than a second threshold; the second battery cell is any other battery cell in the battery pack besides the first battery cell.

[0080] In one possible implementation, the device further includes:

[0081] The early warning unit is used to issue a thermal runaway early warning for the first battery cell if the rate of change of internal resistance of the first battery cell exceeds a first threshold and the duration of the difference between the rate of change of internal resistance of the first battery cell and the rate of change of internal resistance of the second battery cell being greater than a second threshold reaches a third threshold.

[0082] In one possible implementation, the injection unit is used for:

[0083] Detect the vehicle's overall current.

[0084] If the vehicle current is less than or equal to the fourth threshold, the AC current signal is injected into the high voltage of the battery pack.

[0085] In one possible implementation, the monitoring unit is used for:

[0086] Detect the internal resistance of each cell at different times;

[0087] For each cell, the rate of change of the cell's internal resistance is calculated based on the cell's internal resistance at different times.

[0088] In one possible implementation, any one of the different times is taken as the target time, and each battery cell is taken as the target battery cell. The monitoring unit is used for:

[0089] By monitoring the AC current signals at both ends of the target cell, the phase difference between the sampled signal and the injected signal at the target time is obtained:

[0090] The internal resistance of the target cell at the target time is calculated based on the phase difference.

[0091] In one possible implementation, the monitoring unit is used for:

[0092] Extract the signal component of the target frequency from the sampled signal, wherein the target frequency is the frequency of the alternating current signal;

[0093] The internal resistance of the target cell at the target time is obtained by calculating the magnitude and phase difference based on the signal components.

[0094] As can be seen from the above technical solution, the battery packs used in modern vehicles include multiple battery modules, and each battery module includes multiple cells. To monitor the state of the cells in the battery pack and determine whether thermal runaway has occurred, an AC current signal can be injected into the high voltage of the battery pack. Then, the internal resistance of each cell in the battery pack is monitored to obtain the rate of change of internal resistance of each cell. If the rate of change of internal resistance of a cell, such as the first cell, exceeds a first threshold, and the difference between the rate of change of internal resistance of the first cell and the rate of change of internal resistance of other cells, such as the second cell, is greater than a second threshold, it indicates that the internal chemical structure of the first cell may have changed. This change may be due to thermal runaway, and it can be determined that the first cell has experienced thermal runaway. This method can effectively detect the internal resistance of the cells and use impedance data for thermal runaway monitoring. It can effectively monitor the state of the cells, accurately determine whether thermal runaway has occurred, and minimize missed or false detections, so as to provide early warning before thermal runaway and reduce the direct and secondary damage caused by thermal runaway.

[0095] Those skilled in the art will understand that all or part of the steps of the above method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When the program is executed, it performs the steps of the above method embodiments. The aforementioned storage medium can be at least one of the following media: read-only memory (ROM), RAM, magnetic disk, or optical disk, etc., and other media capable of storing program code.

[0096] It should be noted that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for the device and system embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method embodiments. The device and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of the solution in this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0097] The above description is merely one specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for monitoring thermal runaway of a battery cell, characterized in that, The method includes: An alternating current signal is injected into the high voltage of the battery pack, which includes multiple battery modules, each of which includes multiple battery cells; The internal resistance of each cell in the battery pack is monitored to obtain the rate of change of internal resistance of each cell. If the rate of change of internal resistance of the first cell in the plurality of cells exceeds a first threshold, and the difference between the rate of change of internal resistance of the first cell and the rate of change of internal resistance of the second cell is greater than a second threshold, it is determined that the first cell has thermal runaway; the second cell is any other cell in the battery pack besides the first cell.

2. The method according to claim 1, characterized in that, The method further includes: If the rate of change of internal resistance of the first battery cell exceeds a first threshold, and the duration for which the difference between the rate of change of internal resistance of the first battery cell and the rate of change of internal resistance of the second battery cell is greater than a second threshold reaches a third threshold, a thermal runaway warning is issued for the first battery cell.

3. The method according to claim 1, characterized in that, The injection of AC current signal into the high voltage of the battery pack includes: Detect the vehicle's overall current. If the vehicle current is less than or equal to the fourth threshold, the AC current signal is injected into the high voltage of the battery pack.

4. The method according to any one of claims 1-3, characterized in that, The step of monitoring the internal resistance of each cell in the battery pack to obtain the rate of change of internal resistance of each cell includes: Detect the internal resistance of each cell at different times; For each cell, the rate of change of the cell's internal resistance is calculated based on the cell's internal resistance at different times.

5. The method according to claim 4, characterized in that, The method for detecting the internal resistance of a target cell at a given target time, taking any one of the different times as the target time and each cell as the target cell, includes: By monitoring the AC current signals at both ends of the target cell, the phase difference between the sampled signal and the injected signal at the target time is obtained: The internal resistance of the target cell at the target time is calculated based on the phase difference.

6. The method according to claim 5, characterized in that, The step of calculating the internal resistance of the target cell at the target time based on the phase difference includes: Extract the signal component of the target frequency from the sampled signal, wherein the target frequency is the frequency of the alternating current signal; The internal resistance of the target cell at the target time is obtained by calculating the magnitude and phase difference based on the signal components.

7. A monitoring device for thermal runaway of a battery cell, characterized in that, The device includes: An injection unit is used to inject an AC current signal into the high voltage of the battery pack, wherein the battery pack includes multiple battery modules, and each battery module includes multiple cells; The monitoring unit is used to monitor the internal resistance of each of the multiple cells in the battery pack and obtain the rate of change of internal resistance of each cell. The determining unit is configured to determine that the first battery cell has experienced thermal runaway if the rate of change of internal resistance of the first battery cell among the plurality of battery cells exceeds a first threshold and the difference between the rate of change of internal resistance of the first battery cell and the rate of change of internal resistance of the second battery cell is greater than a second threshold; the second battery cell refers to the other battery cells in the battery pack besides the first battery cell.

8. The apparatus according to claim 7, characterized in that, The device further includes: The early warning unit is used to issue a thermal runaway early warning for the first battery cell if the rate of change of internal resistance of the first battery cell exceeds a first threshold and the duration of the difference between the rate of change of internal resistance of the first battery cell and the rate of change of internal resistance of the second battery cell being greater than a second threshold reaches a third threshold.

9. The apparatus according to claim 7, characterized in that, The injection unit is used for: Detect the vehicle's overall current. If the vehicle current is less than or equal to the fourth threshold, the AC current signal is injected into the high voltage of the battery pack.

10. The apparatus according to any one of claims 7-9, characterized in that, The monitoring unit is used for: Detect the internal resistance of each cell at different times; For each cell, the rate of change of the cell's internal resistance is calculated based on the cell's internal resistance at different times.

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