Method and device for identifying abnormal battery cell of battery pack

Abstract

The invention provides a battery pack abnormal cell identification method and device, and relates to the technical field of battery pack production. The battery pack abnormal cell identification method comprises the following steps: discharging a to-be-identified battery pack based on a discharge current so as to adjust each cell in the battery pack to be in an emptying state; charging the discharged battery pack by using the charging current so as to adjust each battery cell in the battery pack to be in a target state, the target state comprising that the charge state of the battery cell is in a target charge state; performing multi-channel impedance test on all the battery packs with the battery cells in the target state, and determining multi-class impedance values of each battery cell; the multiple types of impedance values comprise at least two of an ohmic impedance value, a charge transfer impedance value and a diffusion impedance value; and identifying the battery cells with any type of impedance values greater than the corresponding threshold value in the multiple types of impedance values as abnormal battery cells. Through the method, the abnormal battery cell in the battery pack can be accurately positioned, and the method is suitable for production detection and operation and maintenance troubleshooting of the battery pack module.

Description

Technical Field

[0001] This disclosure relates to the field of battery pack manufacturing technology, specifically to a method and apparatus for identifying abnormal battery cells in a battery pack. Background Technology

[0002] Battery packs generally adopt an architecture design of "cells connected in series to form modules, and multiple modules combined and integrated" to adapt to the voltage and capacity requirements of terminal devices. However, in actual production and use, due to the "weakest link" effect caused by the initial performance of the cells, the cell with the lowest voltage will reach the discharge cutoff voltage first during discharge, and the cell with the highest voltage will reach the charging cutoff voltage first during charging. These phenomena can cause problems such as large voltage differences and low charging capacity during the aging process of the battery pack. As the battery system is used, the voltage difference problem may further amplify, directly affecting the charging and discharging performance of the entire module, resulting in some waste of battery pack capacity. Moreover, cells that are constantly at their full charge and discharge limits will experience capacity decay earlier than other cells, which may lead to safety issues in severe cases.

[0003] In existing technologies, batteries are typically graded before shipment based on parameters such as open circuit voltage (OCV), capacity, 1000Hz alternating current internal resistance (ACIR), and K-value. Before module or battery pack assembly, the batteries undergo further voltage and AC resistance testing to screen out defective cells. However, this method has limited effectiveness in cell screening, failing to intercept problematic cells before battery pack assembly. This increases the probability of defective batteries, leading to time and cost losses in subsequent production, and even the risk of defective battery packs reaching the end market. Summary of the Invention

[0004] This disclosure addresses the problems existing in the prior art by providing a method and apparatus for identifying abnormal battery cells in a battery pack, which can achieve rapid and accurate identification of abnormal battery cells in a battery pack.

[0005] To achieve the above objectives, the technical solution adopted in this disclosure is as follows: A first aspect of this disclosure provides a method for identifying abnormal cells in a battery pack. The method includes: discharging the battery pack to be identified based on a discharge current to adjust each cell in the battery pack to a discharged state, wherein the discharged state includes the cell's voltage being a preset voltage; charging the discharged battery pack with a charging current to adjust each cell in the battery pack to a target state, wherein the target state includes the cell's state of charge being at a target state of charge; the charging current includes a constant charging current or a non-constant charging current; performing a multi-channel impedance test on the battery pack with all cells in the target state to determine multiple impedance values ​​for each cell; the multiple impedance values ​​include at least two of ohmic impedance, charge transfer impedance, and diffusion impedance; and identifying cells whose impedance values ​​of any one of the multiple impedance values ​​are greater than a corresponding threshold as abnormal cells.

[0006] In some embodiments of this disclosure, the discharge current includes a first current with a preset discharge rate and a second current with a fixed current value, wherein the second current is less than the first current, and the charging current includes a constant charging current. Discharging the battery pack based on the discharge current to adjust each cell in the battery pack to a vented state includes: discharging the battery pack once based on the first current; and discharging the battery pack a second time based on the second current to adjust each cell in the battery pack to a vented state.

[0007] In some embodiments of this disclosure, the preset discharge rate includes any discharge rate in the range of 0.5C to 2C, and the second current includes any current value in the range of 150mA to 180mA.

[0008] In some embodiments of this disclosure, before performing multi-channel impedance testing on the battery pack with all cells in the target state, the method further includes: placing the battery pack with all cells in the target state at a set temperature for a preset time, and connecting the battery pack to the impedance testing device via connectors to establish multiple impedance testing channels for the battery pack.

[0009] In some embodiments of this disclosure, the set temperature includes any temperature within the range of 25±2℃, the preset duration includes any duration within the range of 12h to 24h, and the connector type includes any one of one parallel eight-string, one parallel sixteen-string, two parallel eight-string, and two parallel sixteen-string.

[0010] In some embodiments of this disclosure, a multi-channel impedance test is performed on a battery pack with all cells in a target state to determine multiple impedance values ​​for each cell. This includes: within a preset frequency range, scanning the frequency of each cell in the battery pack in parallel through multiple impedance test channels, sequentially applying multiple perturbation signals of different frequencies, and synchronously acquiring the response signal corresponding to each frequency; obtaining the impedance data of each cell based on the perturbation signal and the corresponding response signal of each impedance test channel at each frequency; and fitting the impedance data of each cell to determine multiple impedance values ​​for each cell.

[0011] In some embodiments of this disclosure, the preset frequency range is selected from any sub-range within the range of 0.01 Hz to 20000 Hz.

[0012] In some embodiments of this disclosure, before identifying a battery cell whose impedance value in any of the multiple impedance values ​​is greater than the corresponding threshold as an abnormal battery cell, the method further includes: determining the corresponding threshold for each type of impedance value based on the median and standard deviation of each type of impedance value, wherein the corresponding threshold includes the sum of the product of the preset coefficient and the standard deviation of each type of impedance value and the median.

[0013] In some embodiments of this disclosure, the target state of charge includes any SOC value within the range of 10% SOC to 15% SOC.

[0014] A second aspect of this disclosure provides a battery pack abnormal cell identification device, the device comprising: The coarse adjustment unit is used to discharge the battery pack to be identified based on the discharge current, so as to adjust each cell in the battery pack to a discharged state, the discharged state including the cell voltage being a preset voltage; The fine-tuning unit is used to charge the discharged battery pack with the charging current in order to adjust each cell in the battery pack to a target state, including the cell's state of charge being at a target state of charge; the charging current includes a constant charging current or a non-constant charging current. The determination unit is used to perform multi-channel impedance testing on all battery cells in the target state of the battery pack to determine multiple types of impedance values ​​for each cell; the multiple types of impedance values ​​include at least two of the following: ohmic impedance value, charge transfer impedance value, and diffusion impedance value; the identification unit is used to identify cells whose impedance values ​​of any type of impedance value are greater than the corresponding threshold as abnormal cells.

[0015] This disclosure also provides an electronic device, comprising: a memory for storing at least one instruction; and a processor for calling the instruction stored in the memory to execute the battery pack abnormal cell identification method in the first aspect and any embodiment thereof.

[0016] This disclosure also provides a computer-readable storage medium storing at least one executable instruction, which is loaded and executed by a processor to implement the battery pack abnormal cell identification method in the first aspect and any embodiment of the first aspect.

[0017] This disclosure also provides a computer program product, which includes computer program code. When the computer program code is run by a computer, it causes the computer to execute the battery pack abnormal cell identification method in the first aspect and any embodiment of the first aspect.

[0018] Compared with the prior art, this disclosure has the following beneficial effects: The battery pack abnormal cell identification method provided in this disclosure can eliminate the influence of different cell capacities on impedance data by adjusting each cell in the battery pack to the target state; by performing multi-channel impedance testing on the battery pack, impedance data of each cell in the battery pack can be quickly obtained; by determining multiple types of impedance values ​​for each cell in the battery pack and introducing evaluation of multiple impedance values, the ability to screen abnormal cells can be improved; by identifying any type of impedance value greater than the corresponding threshold as an abnormal cell, abnormal cells can be accurately screened out. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating a method for identifying abnormal battery cells in a battery pack according to an embodiment of this disclosure; Figure 2 This is a schematic diagram of battery pack impedance data provided according to an embodiment of the present disclosure; Figure 3 This is a schematic diagram of various impedance values ​​and corresponding thresholds of a battery pack according to an embodiment of this disclosure; Figure 4 This is a CT scan image of an abnormal battery cell provided according to an embodiment of this disclosure; Figure 5 This is a technical flowchart of a method for identifying abnormal battery cells in a battery pack according to an embodiment of this disclosure; Figure 6 This is a structural block diagram of a battery pack abnormal cell identification device provided according to an embodiment of the present disclosure. Detailed Implementation

[0020] The present disclosure will now be further described with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present disclosure and should not be construed as limiting the scope of protection of the present disclosure. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application.

[0021] The acquisition, transmission, storage, use, and processing of data in this disclosed technical solution comply with relevant national laws and regulations. In the embodiments of this disclosure, certain existing industry solutions such as software, components, and models may be mentioned. These should be considered exemplary, intended only to illustrate the feasibility of implementing the technical solution of this disclosure, and do not imply that the applicant has already used or necessarily used such solutions.

[0022] All terms used in this disclosure have the same meaning as understood by one of ordinary skill in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and not as idealized or highly formalized, unless expressly defined herein.

[0023] The effect of conducting voltage and AC internal resistance tests on the battery again before the assembly of modules or battery packs is limited. It cannot intercept problematic cells before the battery pack is assembled, increasing the probability of "short-term" batteries, causing time and cost losses in subsequent production, and even the risk of defective battery packs flowing into the end market.

[0024] Electrochemical impedance spectroscopy (EIS) can obtain an AC impedance spectrum composed of the response signals of the battery cells at different frequencies. By fitting different components in the equivalent circuit, it can separate the processes involved in the internal electrochemical reactions of the battery in the frequency domain, thereby identifying different causes of battery abnormalities and significantly improving the screening capability for abnormal cells. However, traditional single-channel impedance testing cannot simultaneously test all cells in a series module, resulting in low testing efficiency; and it is prone to data deviation due to factors such as testing time differences and environmental fluctuations, making the test data incomparable. Multi-channel impedance testing can effectively solve the above drawbacks by synchronously obtaining the impedance data of each individual cell in the battery pack, but it is necessary to ensure the stability and accuracy of the response signal during the impedance testing process and eliminate interference factors in multi-channel impedance testing.

[0025] Based on this, a method for identifying abnormal battery cells in a battery pack is provided. Figure 1 This is a flowchart illustrating a method for identifying abnormal battery cells in a battery pack according to an embodiment of this disclosure. Figure 1 As shown, the battery pack abnormal cell identification method includes steps S111 to S13.

[0026] In this embodiment of the disclosure, the above-mentioned method for identifying abnormal battery cells in a battery pack includes: discharging and charging the battery pack to be identified based on the discharge current and the charging current, respectively, to adjust each cell in the battery pack to a target state. Specifically, the above steps include steps S111 and S112.

[0027] Step S111: Discharge the battery pack to be identified based on the discharge current to adjust each cell in the battery pack to a discharged state.

[0028] It should be noted that the battery pack to be identified in this embodiment is composed of at least two cells connected in series and parallel; the discharged state in this embodiment refers to the electrical state in which the releaseable charge inside the cell is basically removed, at which time the cell voltage drops to a preset voltage, that is, the discharged state may include the cell voltage being the preset voltage.

[0029] In some embodiments of this disclosure, the discharge current includes a first current with a preset discharge rate and a second current with a fixed current value, wherein the second current is less than the first current.

[0030] In some embodiments of this disclosure, adjusting each cell in the battery pack to a discharged state may include: discharging the battery pack once based on a first current; and discharging the battery pack a second time based on a second current, so as to adjust each cell in the battery pack to a discharged state.

[0031] In one possible implementation, the preset discharge rate includes any discharge rate in the range of 0.5C to 2C, the second current is any current value in the range of 150mA to 180mA, and the constant charging current is 0.5C. It can be understood that using a large current discharge with a preset discharge rate of 0.5C to 2C can shorten the discharge time, while using a small current discharge of 150mA to 180mA can finely adjust each cell to achieve a discharged state.

[0032] For example, in one specific embodiment, the battery pack can be coarsely adjusted using a charging / discharging device with a preset discharge rate of 0.5C and a large current (100A × 0.5 = 50A when the current is 100A). Then, a fine-tuning device can be used with a small current of 150mA to fine-tune the battery pack. That is, the adjustment of the cell state within the battery pack uses a combination of "coarse adjustment with charging / discharging device + fine adjustment with equalizer" to initially adjust the cell consistency, and then uses the charging / discharging device to charge to a fixed SOC capacity to adjust the target cell state. Performing the above adjustments on the battery pack can eliminate the influence of different cell capacities on the impedance data.

[0033] Additionally, it should be noted that both the primary and secondary discharge processes described above have cutoff voltages. The condition for discharge cutoff includes that the voltage of any cell in the battery pack reaches the cutoff voltage. This can be understood as follows: The battery pack is discharged once with a first current at a preset discharge rate, for example, 0.5C, with a 2.5V cutoff voltage. When the voltage of one cell reaches the cutoff voltage, the discharge stops. Observing the voltage of each cell reveals that the voltages of the remaining cells are still higher than the cutoff voltage. This indicates that the remaining capacity of each cell is inconsistent. If a fixed SOC is applied, the capacity of each cell will still differ significantly. To further reduce this difference, a secondary discharge using a small current is performed after the initial discharge. For example, the battery pack is discharged a second time using a small current of 150mA with a cutoff voltage of 2.5V. For a module with 16 cells, the equalization capacity of these 16 cells during the secondary discharge is as follows (in Ah): 1.46, 0.96, 0.87, 1.01, 0.77, 0.95, 0.86, 1.11, 1.19, 1.24, 0.92, 0.87, 1.21, 0.98, 6.08, 1.29. It can be seen that a small portion of the capacity can still be released during the secondary discharge using an equalizer. From the equalization capacity of a certain cell being 6.08Ah, it can be directly deduced that a significant amount of capacity remains unreleased after the initial discharge. Therefore, the embodiments of this disclosure adopt the method of "coarse adjustment by primary discharge" + "fine adjustment by secondary discharge" to ensure that each cell in the battery pack is fully discharged, thereby ensuring that the capacity of each cell remains consistent after being charged to a fixed SOC.

[0034] In this embodiment, the voltage of all individual cells in the battery pack is simultaneously balanced and discharged to ensure that the starting conditions of all cells are consistent during the subsequent charging stage.

[0035] Step S112: Charge the discharged battery pack with the charging current to adjust each cell in the battery pack to the target state.

[0036] In some embodiments of this disclosure, the charging current includes a constant charging current or a non-constant charging current. It should be noted that, in these embodiments, the charging current refers to the current input from an external power source to a discharged battery pack via a power conversion unit. Its waveform can be a constant value or can vary according to time or voltage; that is, the charging current can include a constant charging current or a non-constant charging current. The non-constant charging current encompasses step current, pulse current, or dynamic current adjusted in real-time by the polarization voltage, used to shorten charging time and reduce polarization effects.

[0037] In some embodiments of this disclosure, the target state includes the cell's state of charge (SOC) being at a target SOC. In one possible implementation, the target SOC includes any SOC value within the range of 10% SOC to 15% SOC. Since the voltage range of a lithium iron phosphate battery during charging and discharging is 2.5V to 3.65V, and the SOC of 10% to 15% SOC is not within the voltage plateau of the lithium iron phosphate battery's charge-discharge curve, the discharge state can be set to a cell voltage reaching 2.5V, and the target state can be set to a cell capacity within the range of 10% to 15% SOC. For example, in one specific embodiment, the battery pack is coarsely adjusted based on the cutoff condition that each cell in the battery pack discharges to 2.5V, and then finely adjusted so that each cell in the battery pack reaches a discharge state of 2.5V. A constant charging current of 0.5C is used to charge for 18 minutes to bring each cell in the battery pack to the target SOC of 15%.

[0038] Step S12: Perform multi-channel impedance testing on all battery packs with all cells in the target state to determine the multi-type impedance values ​​for each cell.

[0039] It should be noted that the various impedance values ​​include at least two of the following: ohmic impedance, charge transfer impedance, and diffusion impedance. Electrochemical impedance spectroscopy (EIS) tests probe the dynamic processes inside the battery by applying small-amplitude AC signals at different frequencies. Since different processes within the battery have different relaxation times (i.e., different response speeds), they can be separated in the frequency domain into: 1) High frequency: the fastest-responding process, i.e., ohmic conduction; 2) Mid-frequency: the slower-responding charge transfer process; 3) Low frequency: the slowest-responding diffusion process. By analyzing the impedance characteristics within these three frequency ranges, the ohmic resistance, charge transfer resistance, and diffusion impedance of the battery can be obtained, respectively. Ohmic impedance mainly reflects the resistance of the electronic and ionic conduction paths within the battery, including the electronic resistance of the electrode materials themselves, the ionic resistance of the electrolyte, the membrane resistance, and the contact resistance of the current collector and leads. Charge transfer impedance reflects the ease or difficulty of the electrochemical reaction; specifically, it corresponds to the process of charge (electrons or ions) transferring across the electric double layer at the electrode / electrolyte interface. In a battery, this is the resistance to the redox reaction of lithium ions on the electrode surface. Diffusion impedance reflects the resistance encountered by active materials during diffusion in the solid phase of the electrode material or the electrolyte. When the electrochemical reaction rate is fast, the diffusion process may become the controlling step of the entire reaction. In one possible implementation, multiple impedance values ​​are used, including ohmic impedance, charge transfer impedance, and diffusion impedance. These three impedances can be used to separate the processes involved in the internal electrochemical reaction of the battery in the frequency domain, thereby identifying different causes of battery abnormalities and improving the screening capability for abnormal cells.

[0040] Understandably, lithium-ion batteries are typically graded before shipment based on parameters such as open-circuit voltage (OCV), capacity, 1000Hz ACIR, and K-value. However, these grading methods primarily fall under the category of electronic resistance testing, with little consideration given to ionic resistance. In this embodiment, when multiple impedance values ​​include charge transfer impedance or diffusion impedance, the introduction of an evaluation of this type of ionic resistance allows the battery grading to more comprehensively reflect its overall electrochemical characteristics.

[0041] Additionally, it should be noted that before performing multi-channel impedance testing on the battery pack, the method includes: placing the battery pack at a set temperature for a preset time, and connecting the battery pack to the impedance testing device via connectors to establish multiple impedance testing channels for the battery pack. Placing the battery pack at a set temperature for a preset time eliminates the influence of ambient temperature, and using connectors eliminates the influence of alligator clips and wiring harnesses on cell voltage acquisition. In other words, by placing the battery pack in a constant-temperature environment for a certain time and using connectors, most interference factors in multi-channel impedance testing, such as test temperature, sampling method, and sampling wiring harnesses, can be eliminated, thus obtaining accurate impedance data capable of comparing and screening abnormal cells.

[0042] In one possible implementation, the set temperature includes any temperature within the range of 25±2℃, the preset duration includes any duration within the range of 12h to 24h, and the connector type includes any one of one parallel eight-series, one parallel sixteen-series, two parallel eight-series, and two parallel sixteen-series. It should be noted that in a battery system, "parallel" refers to connecting several cells or modules in parallel, with the voltage remaining constant while the capacity is added; "series" refers to connecting several cells or modules end-to-end, with the voltage added while the capacity remains constant. In this embodiment, the number of series connections is abbreviated as S, and the number of parallel connections is abbreviated as P. One of the main functions of the connector is to perform voltage sampling and monitoring. The required number of pins or wires directly depends on the total number of series connections in the battery pack, i.e., the total number of cells at the voltage plateau. Since it is necessary to sample the voltage of each cell from the positive to the negative terminal of the entire series link, the number of voltage sampling points = the number of series connections + 1, that is, for an N-series battery pack, there are N+1 voltage sampling points. It is understandable that, since the parallel-connected cells are at the same potential, the number of parallel connections in the battery pack does not affect the number of voltage sampling points. In the embodiments of this disclosure, battery packs with different series-parallel structures, i.e., battery packs of different models, use different types of connectors.

[0043] In one specific embodiment, when the series-parallel combination structure of the battery pack is one parallel and eight series, i.e., 1P8S, it means that it includes one group of parallel cells, each group has eight series cells, i.e., eight cells are connected in series, and the total number of cells is eight. Then the number of voltage sampling points is 8 (S) + 1 = 9. At least a 9-pin connector should be selected to meet the voltage acquisition requirements of eight series batteries.

[0044] In one specific embodiment, when the series-parallel combination structure of the battery pack is one parallel and sixteen series, i.e., 1P16S, it means that it includes one group of parallel connections, each group has 16 series cells, that is, it is composed of 16 cells connected in series, and the total number of cells is 16. Then the number of voltage sampling points is 16 (S) + 1 = 17, corresponding to the selection of at least 17-pin connectors.

[0045] In one specific embodiment, when the battery pack series-parallel combination structure is two parallel eight series, i.e., 2P8S, it means that it includes two groups of parallel connections, each group has 8 series cells, that is, there are two identical 8-series cell links inside. These two links are electrically connected in parallel, and the total number of cells is 16. However, since the battery pack is still an 8-series structure, the number of voltage sampling points is 8(S) + 1 = 9. Since the corresponding points of the two parallel branches have the same potential, a set of 9-pin sampling lines can meet the sampling requirements. Therefore, at least 9-pin connectors are selected.

[0046] In one specific embodiment, when the series-parallel combination structure of the battery pack is two parallel sixteen series, i.e., 2P16S, it means that there are two groups of parallel connections, each group has 16 series cells, the total number of cells is 32, the number of voltage sampling points is 16 (S) + 1 = 17, and at least 17-pin connectors are selected accordingly.

[0047] The temperature, preset duration, and connectors mentioned above can be adjusted appropriately according to actual conditions, and this disclosure does not impose specific limitations on these embodiments. For example, in one specific embodiment, the temperature is set to 26°C, the preset duration is 16 hours, and for the 1P16S battery pack, a 17-pin connector that matches its structure is selected.

[0048] In some embodiments of this disclosure, step S12 may specifically include steps S121 to S123.

[0049] Step S121: Within a preset frequency range, the frequency of each cell in the battery pack is swept in parallel through multiple impedance test channels, and multiple disturbance signals of different frequencies are applied in sequence, while the response signal corresponding to each frequency is collected synchronously.

[0050] In one possible implementation, multiple current disturbance signals of different frequencies can be applied, and the voltage response signal corresponding to each frequency can be collected synchronously; in another possible implementation, multiple voltage disturbance signals of different frequencies can be applied, and the current response signal corresponding to each frequency can be collected synchronously.

[0051] In one possible implementation, the preset frequency range is selected from any sub-range of 0.01 Hz to 20000 Hz. For example, in one specific embodiment, the preset frequency range is 0.01 Hz to 10000 Hz.

[0052] Step S122: Based on the disturbance signal and corresponding response signal of each impedance test channel at each frequency, obtain the impedance data of each cell in the battery pack.

[0053] In one possible implementation, based on the perturbation signal and corresponding response signal of each impedance test channel at each frequency, the complex impedance Z = Z' + jZ'' of each cell in the battery pack can be calculated using Ohm's law, thus obtaining the impedance data of each cell in the battery pack. For example, in a specific embodiment, such as Figure 2 As shown, the horizontal axis represents the real part of impedance Z' (unit: mΩ), representing the resistive component, which is directly related to energy consumption; the vertical axis represents the imaginary part of impedance -Z'' (unit: mΩ), representing the reactive component, which is related to temporary energy storage; the curves of different gray levels in the figure correspond to the impedance data of different cells in the battery pack. Figure 2 As can be seen from the data, cell number 2 exhibits a relatively obvious outlier phenomenon, but whether it is an abnormal cell still needs further confirmation.

[0054] Step S123: Fit the impedance data of each cell to determine the multiple impedance values ​​of each cell.

[0055] In one possible implementation, the impedance data of each cell in the battery pack can be fitted by selecting a suitable equivalent circuit diagram to obtain the specific values ​​of ohmic impedance Rs, charge transfer impedance Rct, and diffusion impedance Rw. The specific steps are as follows: 1) Use ideal components such as resistors, capacitors, and inductors in a certain arrangement and combination (combination principle: able to represent the electrochemical reaction inside the battery under test, so that the impedance spectrum EIS of these ideal components can reproduce the measured AC impedance spectrum as much as possible); 2) Obtain the specific fitting values ​​through the nonlinear least squares method; 3) Increase the number of iterations (until the fitting error of all parameters is less than 10%) to improve the fitting effect.

[0056] Step S13: Identify any battery cell whose impedance value is greater than the corresponding threshold among the multiple impedance values ​​as an abnormal battery cell.

[0057] It should be noted that before identifying any battery cell whose impedance value is greater than the corresponding threshold among multiple impedance values ​​as an abnormal battery cell, the method also includes: determining the corresponding threshold for each type of impedance value based on the median and standard deviation of each type of impedance value. The corresponding threshold is the sum of the product of the preset coefficient and the standard deviation of each type of impedance value and the median.

[0058] In one possible implementation, the threshold values ​​of various impedance values ​​in the battery pack are defined using the variable α coefficient of 1.5 in the "median + α × standard deviation" model. That is, the corresponding threshold = median + 1.5 × standard deviation. Choosing α = 1.5 as the anomaly detection coefficient can obtain a better solution between detection capability and false alarm rate, effectively identifying meaningful outliers while avoiding over-detection, thus meeting the safety and consistency requirements of the battery system. For example, in a specific embodiment, ... Figure 2 The impedance data of each cell in the battery pack are fitted to obtain various impedance values ​​for each cell in the battery pack, such as... Figure 3 As shown in the figure, the three gray bar charts represent the ohmic impedance Rs, charge transfer impedance Rct, and diffusion impedance Rw values ​​for cells 1 to 15, respectively. The three horizontal solid lines represent the corresponding threshold values ​​for ohmic impedance Rs, charge transfer impedance Rct, and diffusion impedance Rw.

[0059] For example, in one specific embodiment, assuming that one module in the battery pack contains 8 cells, the ohmic impedance values ​​(unit: mΩ) of each cell are obtained through testing as follows: 15.2, 15.5, 15.3, 18.9, 15.1, 15.7, 15.5, 20.3. The median is calculated to be 15.55, and the standard deviation is calculated to be 1.83. The corresponding threshold T is calculated as "median + 1.5 × standard deviation" = 15.55 + 1.5 × 1.83 ≈ 18.30 mΩ. The ohmic impedance values ​​of the 12 cells are compared with the corresponding threshold (18.30 mΩ). Cells with values ​​greater than the corresponding threshold are considered abnormal cells. Among them, cell No. 4 has an ohmic impedance of 18.9mΩ > 18.30mΩ, and is identified as an abnormal cell; cell No. 8 has an ohmic impedance of 20.3mΩ > 18.30mΩ, and is identified as an abnormal cell; the ohmic impedance values ​​of the remaining 6 cells are all below 18.30mΩ, and are identified as normal cells.

[0060] For example, according to Figure 3 As can be seen, the ohmic impedance Rs and charge transfer impedance Rct of cell No. 2 are significantly greater than the corresponding thresholds, accurately identifying it as an abnormal cell. To further verify that cell No. 2 is an abnormal cell, a CT scan was performed on it, and the CT image of cell No. 2 is shown below. Figure 4 As shown in the CT scan, the positive electrode tab of the battery cell is broken, confirming that it is an abnormal battery cell.

[0061] The battery pack abnormal cell identification method provided above can effectively filter out abnormal outlier data that exceeds the corresponding threshold, and accurately identify abnormal cells in the battery pack.

[0062] In one possible implementation, Figure 5 This is a technical flowchart of a method for identifying abnormal battery cells in a battery pack according to an embodiment of this disclosure, as shown below. Figure 5 As shown, the technical flow of this battery pack abnormal cell identification method can be divided into steps 25, 26, 27, and 28. Step 25 includes: discharging with a charging / discharging device, specifically, discharging with a 0.5C current until the voltage of a single cell reaches 2.5V; discharging with an equalizer, specifically, discharging with a 150mA current until the voltage of each single cell in the battery pack reaches 2.5V; charging with a charging / discharging device, specifically, charging with a fixed 0.5C current for 18 minutes to adjust the capacity of each cell in the pack to 15% SOC. Step 26 includes: placing the battery pack in a constant temperature room or incubator and selecting connectors, specifically, placing it in a constant temperature environment of 25±2℃ for 24 hours and selecting dedicated connectors according to the battery pack model. Step 27 includes: multi-channel impedance testing, specifically, selecting a frequency range of 0.1 Hz to 10000 Hz and applying a 3A current disturbance to the battery pack; obtaining impedance data, specifically, obtaining the impedance data of each cell from the AC current signal and its voltage response signal. Step 28 includes: impedance data fitting, specifically, fitting the specific values ​​of the ohmic impedance Rs, charge transfer impedance Rct, and diffusion impedance Rw of each cell from the equivalent circuit diagram; impedance outlier screening, specifically, screening outlier data exceeding the threshold when the variable α coefficient in the "median + α × standard deviation" model is 1.5, and identifying abnormal cells in the battery pack module.

[0063] The above technical flowchart uses a combination of "coarse adjustment of charging and discharging equipment + fine adjustment of equalizer" to adjust the consistency of the cells in the early stage and to adjust the state of the cells in the battery pack by charging and discharging equipment with a fixed SOC capacity in the later stage. This can eliminate the influence of cell capacity on impedance testing. Further temperature adaptation and data collection by dedicated connectors are used to eliminate interference factors during testing. Outlier impedance data are screened out when the variable α coefficient in the "median + α × standard deviation" model is 1.5, which can accurately locate abnormal cells in the battery pack module.

[0064] The above-mentioned method for identifying abnormal battery cells in a battery pack is illustrated below with reference to specific embodiments.

[0065] Example 1: A method for identifying abnormal battery cells in a battery pack, which is implemented according to the following steps.

[0066] Step (1) Adjusting the state of the cells in the battery pack: Discharge the battery pack using a large current of 0.5 C with the discharge rate of the charging and discharging equipment. Perform coarse adjustment of the battery pack state by discharging the individual lithium battery cells in the battery pack to the cutoff condition of 2.5V. Discharge the coarsely adjusted battery pack again with a small current of 150 mA using an equalizer. Finely adjust each cell in the battery pack to reach a discharge state of 2.5V. Charge the finely adjusted battery pack with a fixed charging current of 0.5 C for 18 minutes so that each cell in the module is in the target state of 15% SOC.

[0067] Step (2) Eliminate interference factors in multi-channel impedance testing: Place the battery pack with the cell SOC state adjusted in Step 1 in a constant temperature environment of 25±2℃ for 24 hours to stabilize the temperature of the cells at 25±2℃, thus fixing the temperature factor during battery pack impedance testing. Select pre-made dedicated connectors according to the battery pack model to eliminate the influence of alligator clips and wiring harness on cell voltage acquisition.

[0068] Step (3): Obtain the impedance data of each cell in the battery pack: Select the frequency range of 0.1 Hz to 10000 Hz, give the battery pack different frequencies of current disturbance, and collect the voltage response signals at different frequencies. From the AC signals at different frequencies and the response signals they generate, the impedance data of each cell in the series battery pack module can be obtained synchronously through Ohm's law.

[0069] Step (4) Identify abnormal cells in the battery pack: Select a suitable equivalent circuit diagram to fit the impedance data of each cell in the battery pack to obtain the specific values ​​of ohmic impedance Rs, charge transfer impedance Rct, and diffusion impedance Rw. Use the threshold of 1.5 for the variable α coefficient in the "median + α × standard deviation" model to define various impedance values ​​in the battery pack, filter out abnormal outliers that exceed the threshold, and then identify abnormal cells in the battery pack module.

[0070] Example 2: A method for identifying abnormal battery cells in a battery pack. Based on Example 1, some operations and parameters are adjusted, while the remaining operations and parameters remain the same as in Example 1. The specific steps are as follows.

[0071] Step (1): Adjust the state of the cells in the battery pack: adjust the discharge rate of the charging and discharging equipment to 1.0 C, and adjust the target state of each cell to 10% SOC.

[0072] Step (2) Eliminate interference factors in multi-channel impedance testing: Adjust the placement time in a constant temperature environment to 16 h.

[0073] Step (3): Obtain the impedance data of each cell in the battery pack: adjust the frequency range to 0.1 Hz~20000 Hz.

[0074] Step (4): Identify abnormal cells in the battery pack.

[0075] Example 3: A method for identifying abnormal battery cells in a battery pack. Based on Example 1, some operations and parameters are adjusted, while the remaining operations and parameters remain the same as in Example 1. The specific steps are as follows.

[0076] Step (1): Adjust the state of the cells in the battery pack: adjust the discharge rate of the charging and discharging equipment to 2C and the discharge current of the equalizer to 180 mA.

[0077] Step (2) Eliminate interference factors in multi-channel impedance testing: Adjust the placement time in a constant temperature environment to 12 h.

[0078] Step (3): Obtain the impedance data of each cell in the battery pack.

[0079] Step (4): Identify abnormal cells in the battery pack.

[0080] This disclosure also provides a battery pack abnormal cell identification device. Figure 6 This is a structural block diagram of a battery pack abnormal cell identification device provided according to an embodiment of this disclosure, such as... Figure 6 As shown, the device 100 includes a coarse adjustment unit 111, a fine adjustment unit 112, a determination unit 120, and an identification unit 130.

[0081] In this embodiment of the present disclosure, the above-mentioned abnormal cell identification device for a battery pack includes: an adjustment unit, used to discharge and charge the battery pack to be identified based on the discharge current and the charging current respectively, so as to adjust each cell in the battery pack to a target state. Specifically, the adjustment unit includes a coarse adjustment unit 111 and a fine adjustment unit 112.

[0082] The coarse adjustment unit 111 is used to discharge the battery pack to be identified based on the discharge current, so as to adjust each cell in the battery pack to a discharged state, wherein the discharged state includes the cell voltage being a preset voltage. The fine-tuning unit 112 is used to charge the discharged battery pack with the charging current in order to adjust each cell in the battery pack to a target state; the target state includes the cell being in a target state of charge; the charging current includes a constant charging current or a non-constant charging current. The determination unit 120 is used to perform multi-channel impedance testing on the battery pack with all cells in the target state to determine multiple types of impedance values ​​for each cell; the multiple types of impedance values ​​include at least two of the following: ohmic impedance value, charge transfer impedance value, and diffusion impedance value. The identification unit 130 is used to identify cells whose impedance values ​​are greater than the corresponding threshold among multiple types of impedance values ​​as abnormal cells.

[0083] For specific details and benefits of the battery pack abnormal cell identification device provided in the embodiments of this disclosure, please refer to the above description of the battery pack abnormal cell identification method, which will not be repeated here.

[0084] This disclosure also provides an electronic device, comprising: a memory for storing at least one instruction; and a processor for calling the instruction stored in the memory to execute the battery pack abnormal cell identification method in any of the above embodiments.

[0085] This disclosure also provides a computer-readable storage medium storing at least one executable instruction, which is loaded and executed by a processor to implement the battery pack abnormal cell identification method in any of the above embodiments.

[0086] This disclosure also provides a computer program product, which includes computer program code. When the computer program code is run by a computer, it causes the computer to execute the battery pack abnormal cell identification method in any of the above embodiments.

[0087] Those skilled in the art will understand that embodiments of this disclosure can be provided as methods, systems, or computer program products. Therefore, this disclosure can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this disclosure can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0088] This disclosure is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create a machine for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0089] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0090] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0091] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0092] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0093] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0094] It should be noted that the terms "first," "second," and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different parts. Terms such as "including" or "contains" mean that the element preceding the word covers the element listed after the word, and do not exclude the possibility of covering other elements as well.

[0095] Finally, it should be noted that the above content is only used to illustrate the technical solution of this disclosure, and is not intended to limit the scope of protection of this disclosure. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of this disclosure do not depart from the substance and scope of the technical solution of this disclosure.

Claims

1. A method for identifying abnormal battery cells in a battery pack, characterized in that, The methods include: The battery pack to be identified is discharged based on the discharge current to adjust each cell in the battery pack to a discharged state, wherein the discharged state includes the cell voltage being a preset voltage. The battery pack after discharge is charged using a charging current to adjust each cell in the battery pack to a target state, the target state including the state of charge of the cell being in a target state of charge; the charging current includes a constant charging current or a non-constant charging current; Multi-channel impedance testing is performed on the battery pack with all cells in the target state to determine multiple impedance values ​​for each cell; the multiple impedance values ​​include at least two of ohmic impedance, charge transfer impedance, and diffusion impedance. Cells with any impedance value greater than the corresponding threshold among the multiple impedance values ​​are identified as abnormal cells.

2. The battery pack abnormal cell identification method according to claim 1, characterized in that, The discharge current includes a first current using a preset discharge rate and a second current using a fixed current value, wherein the second current is less than the first current. Discharging the battery pack based on the discharge current to adjust each cell in the battery pack to a discharged state includes: The battery pack is discharged once based on the first current; The battery pack is discharged a second time based on the second current to adjust each cell in the battery pack to the vented state.

3. The battery pack abnormal cell identification method according to claim 2, characterized in that, The preset discharge rate includes any discharge rate in the range of 0.5C to 2C, and the second current includes any current value in the range of 150mA to 180mA.

4. The battery pack abnormal cell identification method according to claim 1, characterized in that, Before performing multi-channel impedance testing on the battery pack with all cells in the target state, the method further includes: The battery pack with all cells in the target state is left to stand at a set temperature for a preset time, and the battery pack is connected to an impedance testing device via connectors to establish multiple impedance testing channels for the battery pack.

5. The battery pack abnormal cell identification method according to claim 4, characterized in that, The set temperature includes any temperature within the range of 25±2℃, the preset duration includes any duration within the range of 12h~24h, and the connector type includes any one of one parallel eight-string, one parallel sixteen-string, two parallel eight-string, and two parallel sixteen-string.

6. The battery pack abnormal cell identification method according to claim 4, characterized in that, The process of performing multi-channel impedance testing on the battery pack with all cells in the target state to determine multiple impedance values ​​for each cell includes: Within a preset frequency range, the frequency of each cell in the battery pack is swept in parallel through the multiple impedance test channels, and multiple disturbance signals of different frequencies are applied in sequence, while the response signal corresponding to each frequency is collected synchronously. Based on the disturbance signal and corresponding response signal of each impedance test channel at each frequency, the impedance data of each cell is obtained; The impedance data of each of the battery cells is fitted to determine multiple impedance values ​​for each of the battery cells.

7. The battery pack abnormal cell identification method according to claim 6, characterized in that, The preset frequency range is selected from any sub-range within the range of 0.01 Hz to 20000 Hz.

8. The battery pack abnormal cell identification method according to claim 1, characterized in that, Before identifying any battery cell whose impedance value among the multiple impedance values ​​is greater than the corresponding threshold as an abnormal battery cell, the method further includes: Based on the median and standard deviation of each type of impedance value, a corresponding threshold is determined for each type of impedance value. The corresponding threshold includes the sum of the product of the preset coefficient of each type of impedance value and the standard deviation, and the median.

9. The battery pack abnormal cell identification method according to any one of claims 1-8, characterized in that, The target state of charge includes any SOC value within the range of 10% SOC to 15% SOC.

10. A battery pack abnormal cell identification device, characterized in that, The device includes: The coarse adjustment unit is used to discharge the battery pack to be identified based on the discharge current, so as to adjust each cell in the battery pack to a discharged state, wherein the discharged state includes the cell voltage being a preset voltage; The fine-tuning unit is used to discharge and charge the battery pack after discharge using a charging current, so as to adjust each cell in the battery pack to a target state, the target state including the state of charge of the cell being in a target state of charge; the charging current includes a constant charging current or a non-constant charging current; A determining unit is used to perform multi-channel impedance testing on the battery pack with all cells in the target state, and to determine multiple impedance values ​​for each cell; the multiple impedance values ​​include at least two of ohmic impedance, charge transfer impedance, and diffusion impedance. The identification unit is used to identify any battery cell whose impedance value is greater than the corresponding threshold among the multiple types of impedance values ​​as an abnormal battery cell.

Images