Battery cell anomaly detection method, device, equipment and medium

Abstract

The invention provides a battery cell anomaly detection method, device, equipment and medium, and relates to the technical field of battery cells, and the method comprises the steps: carrying out the capacitance grading detection of a battery cell, adding an impedance test, obtaining the voltage of a first type of battery cells at the beginning of the capacitance grading detection, and obtaining the voltage of a second type of battery cells at different test stages of the impedance test; and obtaining the electrical core impedance obtained by the impedance test. The first type of battery cell voltage is the initial voltage of the battery cell at the beginning of capacity grading detection, the second type of battery cell voltage comprises the voltage of the battery cell at different moments after discharging, and the stability of the voltage drop of the battery cell in unit time can be determined based on the first type of battery cell voltage and the second type of battery cell voltage; the method combines the impedance of the battery cell and the stability of the voltage drop in the unit time to carry out anomaly detection on the battery cell, and compared with a method for judging whether the battery cell is abnormal or not by observing the change trend of the open-circuit voltage through long-time standing, the method is shorter in time consumption.

Description

Technical Field

[0001] The present invention relates to the field of battery cell technology, and in particular to a battery cell abnormality detection method, device, equipment and medium. Background Art

[0002] Lithium-ion batteries are popular in 3C, power and other fields due to their high energy density, high safety, small size and customizability. In the production and manufacturing process of lithium-ion batteries, high temperature and room temperature static methods are usually used to identify abnormal cells. For example, by adjusting the temperature and time variables, the change of the open circuit voltage of the cell over time is obtained, so as to achieve early identification of abnormal defective cells. However, the detection of abnormal open circuit voltage generally takes several days, which has a high time cost and is not conducive to improving production capacity. Summary of the invention

[0003] Based on this, it is necessary to provide a method, device, equipment and medium for abnormality detection of battery cells in response to the above technical problems, so as to solve the problem that abnormality detection of battery cells takes a long time.

[0004] A first aspect of an embodiment of the present application provides a method for detecting abnormalities in a battery cell, the method comprising: obtaining a first type of battery cell voltage at the beginning of a capacity division detection and a collection time of the first type of battery cell voltage; obtaining a second type of battery cell voltage at different test stages in an impedance test and a collection time of the second type of battery cell voltage, the impedance test being started after the capacity division detection is completed; obtaining the battery cell impedance obtained by the impedance test; calculating a voltage drop sequence of the battery cell according to the first type of battery cell voltage, the second type of battery cell voltage, the collection time of the first type of battery cell voltage and the collection time of the second type of battery cell voltage, the voltage drop sequence including values ​​of the voltage drop at different times per unit time; determining whether the battery cell is an abnormal battery cell according to the voltage drop sequence of the battery cell and the battery cell impedance.

[0005] In one embodiment, determining whether the battery cell is an abnormal battery cell based on the voltage drop sequence of the battery cell and the battery cell impedance includes: performing an impedance consistency analysis on a batch of battery cells based on the battery cell impedance, and marking battery cells that do not meet the impedance consistency as abnormal batteries; performing an aging degree consistency analysis on unmarked battery cells based on the voltage drop sequence of the battery cells, and marking battery cells that do not meet the aging degree consistency as abnormal batteries.

[0006] In one embodiment, the impedance consistency analysis is performed on the batch of battery cells based on the battery cell impedance, and the battery cells that do not meet the impedance consistency are marked as abnormal batteries, including: superimposing a first preset fluctuation threshold on the impedance mean of the batch of battery cells to determine a consistency screening range corresponding to the impedance; and marking the battery cells whose impedance is not within the consistency screening range corresponding to the impedance as abnormal batteries.

[0007] In one embodiment, before superimposing the first preset fluctuation threshold on the impedance mean value of the batch of battery cells, the method further includes: calculating an impedance characteristic value of the batch of battery cells, the characteristic value characterizing the impedance distribution of the batch of battery cells; determining a battery cell whose impedance is discrete relative to the characteristic value, and marking the battery cell as an abnormal battery cell; superimposing the first preset fluctuation threshold on the impedance mean value of the batch of battery cells includes: determining an impedance mean value corresponding to unmarked batteries in the batch of battery cells; and superimposing the first preset fluctuation threshold on the impedance mean value corresponding to the unmarked batteries.

[0008] In one embodiment, the impedance test includes an AC impedance test and a DC impedance test, and obtaining the second type of battery cell voltage at different test stages in the impedance test includes: performing the AC impedance test after the capacity division detection, and obtaining the battery cell voltage at the end of the AC impedance test as the second type of battery cell voltage; performing the DC impedance test after the AC impedance test, and obtaining the battery cell voltage at the end of each discharge stage during the DC impedance test as the second type of battery cell voltage; the DC impedance test includes performing stage discharge on the battery cell with different discharge currents and discharge durations.

[0009] In one embodiment, the battery cell impedance includes the AC impedance obtained by the AC impedance test and the DC internal resistance obtained by the DC impedance test, and the AC impedance includes the battery cell ohmic internal resistance, the membrane impedance of the solid electrolyte interface membrane and the charge transfer impedance; the method also includes: calculating the sum of the battery cell ohmic internal resistance, the membrane impedance and the charge transfer impedance of the battery cell as the total AC impedance of the battery cell; calculating the ratio of the total AC impedance of the battery cell to the DC internal resistance; judging whether the ratio is within a preset ratio range, and if not, marking the battery cell as an abnormal battery cell.

[0010] In one embodiment, the preset ratio range is determined according to a second preset fluctuation threshold value and a ratio of a total AC impedance value to a DC internal resistance value measured when the battery cell is in a maximum state of charge.

[0011] A second aspect of an embodiment of the present application provides an abnormality detection device for a battery cell, the device comprising: a first acquisition module, used to acquire a first type of battery cell voltage at the beginning of a capacity division detection and a collection time of the first type of battery cell voltage; a second acquisition module, used to acquire a second type of battery cell voltage at different test stages in an impedance test and a collection time of the second type of battery cell voltage, the impedance test being started after the capacity division detection is completed; a third acquisition module, used to acquire the battery cell impedance obtained by the impedance test; a calculation module, used to calculate a voltage drop sequence of the battery cell according to the first type of battery cell voltage, the second type of battery cell voltage, the collection time of the first type of battery cell voltage and the collection time of the second type of battery cell voltage, the voltage drop sequence including values ​​of the voltage drop at different times per unit time; an abnormality detection module, used to determine whether the battery cell is an abnormal battery cell according to the voltage drop sequence of the battery cell and the battery cell impedance.

[0012] In one embodiment, the abnormality detection module is used to: perform impedance consistency analysis on a batch of battery cells based on the battery cell impedance, and mark the battery cells that do not meet the impedance consistency as abnormal battery cells; perform aging consistency analysis on unmarked battery cells based on the voltage drop sequence of the battery cells, and mark the battery cells that do not meet the aging consistency as abnormal battery cells.

[0013] In one embodiment, the abnormality detection module is used to: superimpose a first preset fluctuation threshold on the impedance mean of the batch of battery cells to determine a consistency screening range corresponding to the impedance; and mark the battery cells whose impedance is not within the consistency screening range corresponding to the impedance as abnormal battery cells.

[0014] In one embodiment, the abnormality detection module is used to: calculate the impedance characteristic value of the batch of battery cells, the characteristic value characterizing the impedance distribution of the batch of battery cells; determine the battery cells whose impedance is discrete relative to the characteristic value, and mark the battery cells as abnormal batteries; determine the impedance mean value corresponding to the unmarked battery cells in the batch of battery cells; and superimpose the first preset fluctuation threshold on the impedance mean value corresponding to the unmarked battery cells.

[0015] In one embodiment, the impedance test includes an AC impedance test and a DC impedance test, and the second acquisition module is used to: perform the AC impedance test after the capacity division detection, and obtain the battery cell voltage at the end of the AC impedance test as the second type of battery cell voltage; perform the DC impedance test after the AC impedance test, and obtain the battery cell voltage at the end of each discharge stage during the DC impedance test as the second type of battery cell voltage; the DC impedance test includes staged discharge of the battery cell with different discharge currents and discharge durations.

[0016] In one embodiment, the battery cell impedance includes the AC impedance obtained by the AC impedance test and the DC internal resistance obtained by the DC impedance test, and the AC impedance includes the battery cell ohmic internal resistance, the membrane impedance of the solid electrolyte interface membrane and the charge transfer impedance; the abnormality detection module is also used to: calculate the sum of the battery cell ohmic internal resistance, the membrane impedance and the charge transfer impedance of the battery cell as the total AC impedance of the battery cell; calculate the ratio of the total AC impedance of the battery cell to the DC internal resistance; determine whether the ratio is within a preset ratio range, and if not, mark the battery cell as an abnormal battery cell.

[0017] In one embodiment, the preset ratio range is determined according to a second preset fluctuation threshold value and a ratio of a total AC impedance value to a DC internal resistance value measured when the battery cell is in a maximum state of charge.

[0018] A third aspect of an embodiment of the present application provides a lithium-ion battery capacity fractionation device, the device comprising a battery cell abnormality detection module; the battery cell abnormality detection module is used to execute the steps of the battery cell abnormality detection method as described in any of the above embodiments.

[0019] A fourth aspect of an embodiment of the present application provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for detecting abnormalities in a battery cell as described in any embodiment of the first aspect above is implemented.

[0020] In summary, the present invention provides a method, device, equipment and medium for detecting abnormalities of battery cells. After performing capacity division detection on the battery cells, an impedance test is added, and the voltage of the first type of battery cells and the collection time of the voltage of the first type of battery cells at the beginning of the capacity division detection are obtained, as well as the voltage of the second type of battery cells and the collection time of the voltage of the second type of battery cells at different test stages of the impedance test, and the battery cell impedance obtained by the impedance test is obtained; then, according to the voltage of the first type of battery cells, the collection time of the voltage of the first type of battery cells, each voltage of the second type of battery cells and the collection time of the voltage of the second type of battery cells, the voltage drop sequence of the battery cells is determined, and the voltage drop sequence includes the values ​​of the voltage drop per unit time at different times; finally, according to the voltage drop sequence of the battery cells and the battery cell impedance, it is determined whether the battery cell is an abnormal battery cell. The present application performs an impedance test after the capacity division detection to test the impedance of the battery cell in a stable state and improve the accuracy of the impedance test; the voltage of the first type of battery cell is the initial voltage of the battery cell when the capacity division detection starts, and the voltage of the second type of battery cell includes the voltage of the battery cell at different times after discharge. The stability of the voltage drop of the battery cell per unit time can be determined based on the voltage of the first type of battery cell and the voltage of the second type of battery cell. The present application performs abnormality detection on the battery cell in combination with the impedance of the battery cell and the stability of the voltage drop per unit time. Compared with judging whether the battery cell has an abnormality by observing the changing trend of the open circuit voltage for a long time, the present application takes less time. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0022] Figure 1 A schematic diagram of a flow chart of a method for detecting abnormality of a battery cell provided in one embodiment of the present application; Figure 2 A schematic flow chart of a method for detecting abnormality of a battery cell provided in another embodiment of the present application; Figure 3 A schematic flow chart of a method for detecting abnormality of a battery cell provided in another embodiment of the present application; Figure 4 A schematic flow chart of a method for detecting abnormality of a battery cell provided in another embodiment of the present application; Figure 5 A schematic flow chart of a method for detecting abnormality of a battery cell provided in another embodiment of the present application; Figure 6 A schematic flow chart of a method for detecting abnormality of a battery cell provided in another embodiment of the present application; Figure 7 A schematic block diagram of a battery cell abnormality detection device provided in one embodiment of the present application; Figure 8 It is a schematic block diagram of a lithium-ion battery capacity conversion device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0025] It should also be understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0026] As used in the present specification and the appended claims, the term “if” may be interpreted as “when” or “uponce” or “in response to determining”, depending on the context. Similarly, the phrases “if it is determined” or “if matched to [described condition or event]” may be interpreted as meaning “upon determination” or “in response to determination” or “uponce matched to [described condition or event]” or “in response to matching to [described condition or event]”, depending on the context.

[0027] In addition, in the description of the present specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0028] References to "one embodiment" or "some embodiments" etc. described in the present specification mean that one or more embodiments of the present invention include specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the statements "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in other ways.

[0029] It should be understood that the size of the serial numbers of the steps in the following embodiments does not mean the order of execution. The execution order of each process should be determined by the coating control party based on its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0030] The battery cell abnormality detection method proposed in the embodiment of the present application can be applied to lithium-ion battery capacity splitting equipment, and the equipment is compatible with AC impedance testing, DC impedance testing, and voltage detection functions. By applying the battery cell abnormality detection method proposed in the present application, the battery cell abnormality detection is realized in the task of battery cell capacity splitting, and the abnormality is recognized in advance. There is no need to obtain the change of the battery cell open circuit voltage by standing still for a long time, thereby shortening the time consumption of battery cell abnormality detection.

[0031] In addition, the abnormality detection method of the battery cell proposed in the embodiment of the present application can also be used in other electronic devices, such as a controller, a terminal device, or a device where the abnormality detection device of the battery cell proposed in the present application is located, etc. This embodiment uses a lithium-ion battery capacity conversion device as the execution subject to exemplify the implementation method of the abnormality detection method of the battery cell provided in the present application.

[0032] like Figure 1 As shown, an embodiment of the present application provides a method for detecting abnormality of a battery cell, which may include the following steps: S101, obtaining a voltage of a first type of battery cell when a capacity division detection starts and a time at which the voltage of the first type of battery cell is collected.

[0033] Illustratively, when the lithium-ion battery capacity splitting device starts to perform capacity splitting detection on a certain battery cell, the voltage of the battery cell is first collected. For the convenience of distinction, the application records the voltage as the first type of battery cell voltage.

[0034] When obtaining the voltage of the first type of battery cell, the lithium-ion battery capacity dividing device records the collection time of the voltage of the first type of battery cell.

[0035] Usually, after the battery cells are produced, they are divided into different capacities and tested for abnormalities before they are put into use. The battery cells involved in the test can be multiple battery cells produced in the same batch, or battery cells that need to be applied to the same product. Alternatively, they can be multiple battery cells in the same battery pack.

[0036] The lithium-ion battery capacity splitting device obtains the voltage of the first type of battery cell and the collection time of the voltage of the first type of battery cell when the capacity splitting detection starts for each battery cell that needs to participate in the abnormality detection.

[0037] S102, obtaining the voltage of the second type of battery cells at different test stages in an impedance test and the collection time of the voltage of the second type of battery cells, wherein the impedance test is started after the capacity division detection is completed.

[0038] For example, the impedance test is used to test the impedance of the battery cell. The complete impedance test process can be divided into multiple test phases as needed.

[0039] The lithium-ion battery capacity fractionation equipment obtains the cell voltage at different test stages. For the convenience of distinction, the cell voltage is recorded as the second-category cell voltage, and the collection time of each second-category cell voltage is recorded.

[0040] In some embodiments, the impedance test may be started after the capacitance division detection is completed.

[0041] The capacity division test process includes charging and discharging of the battery cell, which will stabilize the electrode structure and internal state of the battery cell. Impedance testing in a stable state after capacity division can more accurately reflect the actual impedance inside the battery cell. For example, before capacity division, there may be incompletely activated areas on the electrode surface of the battery cell, which will affect the accuracy of the impedance test. After capacity division charging and discharging, the electrode active substances fully participate in the reaction, and the test results can truly reflect the overall performance of the battery cell.

[0042] S103, obtaining the cell impedance obtained by impedance testing.

[0043] Exemplarily, in addition to providing the capacity splitting function, the lithium-ion battery capacity splitting equipment is also compatible with impedance testing and voltage testing functions. After performing different types of impedance tests on the battery cells, the lithium-ion battery capacity splitting equipment obtains the battery cell impedances obtained by the various impedance tests.

[0044] S104, calculating a voltage drop sequence of the battery cells according to the first type of battery cell voltage, the second type of battery cell voltage, the collection time of the first type of battery cell voltage and the collection time of the second type of battery cell voltage, wherein the voltage drop sequence includes values ​​of the voltage drop at different times within a unit time.

[0045] Illustratively, after performing capacity detection and impedance testing on battery cells, the lithium-ion battery capacity fractionation equipment may record battery cell voltages collected at multiple collection times, and these battery cell voltages may include a first type of battery cell voltage and multiple second type of battery cell voltages.

[0046] As a feasible implementation method, the voltage of the first type of battery cell and any second type of battery cell voltage can be subtracted to obtain a voltage drop, and the voltage drop can be divided by the collection time interval between the first type of battery cell voltage and the second type of battery cell voltage to obtain the value of the voltage drop per unit time at the collection moment of the second type of battery cell voltage.

[0047] The above-mentioned first type of battery cell voltage and second type of battery cell voltage may be the open circuit voltage of the battery cell, and the voltage drop per unit time may be used as the self-discharge rate coefficient of the battery cell, that is, the K value.

[0048] For example, the voltage of the first type of battery cell measured at the beginning of the capacity division test is V1, and the collection time is T1. The voltage of the second type of battery cell measured at the end of the first test phase of the impedance test is V2, and the collection time is T2. The voltage of the second type of battery cell measured at the end of the second test phase is V3, and the collection time is T3. Then the value of the voltage drop per unit time at the time T2 can be (V1-V2) / (T1-T2); the value of the voltage drop per unit time at the time T3 can be (V1-V3) / (T1-T3).

[0049] The “cell voltage drop sequence” in the above step S104 may include the values ​​of the voltage drop per unit time at different times.

[0050] S105 , determining whether the battery cell is an abnormal battery cell according to the voltage drop sequence of the battery cell and the battery cell impedance.

[0051] Exemplarily, it is determined whether the cell impedance of the cell meets the preset impedance standard. If not, the cell is determined as an abnormal cell. For a single cell, the voltage drop sequence of the cell is referred to to determine the fluctuation degree of the voltage drop at different times per unit time, and the cell with a larger fluctuation is determined as an abnormal cell.

[0052] To summarize, the method for detecting abnormality of a battery cell proposed in the embodiment of the present application adds an impedance test after performing capacity division detection on the battery cell, and obtains the first type of battery cell voltage and the collection time of the first type of battery cell voltage at the beginning of the capacity division detection, as well as obtains the second type of battery cell voltage and the collection time of the second type of battery cell voltage at different test stages of the impedance test, and obtains the battery cell impedance obtained by the impedance test; then, according to the first type of battery cell voltage, the collection time of the first type of battery cell voltage, each second type of battery cell voltage and the collection time of the second type of battery cell voltage, the voltage drop sequence of the battery cell is determined, and the voltage drop sequence includes the values ​​of the voltage drop per unit time at different times; finally, according to the voltage drop sequence of the battery cell and the battery cell impedance, it is determined whether the battery cell is an abnormal battery cell. The present application performs an impedance test after the capacity division detection to test the impedance of the battery cell in a stable state and improve the accuracy of the impedance test; the voltage of the first type of battery cell is the initial voltage of the battery cell when the capacity division detection starts, and the voltage of the second type of battery cell includes the voltage of the battery cell at different times after discharge. The stability of the voltage drop of the battery cell per unit time can be determined based on the voltage of the first type of battery cell and the voltage of the second type of battery cell. The present application performs abnormality detection on the battery cell in combination with the impedance of the battery cell and the stability of the voltage drop per unit time. Compared with judging whether the battery cell has an abnormality by observing the changing trend of the open circuit voltage for a long time, the present application takes less time.

[0053] Based on the above embodiments, Figure 2 As shown, in the above step S105, "determining whether the battery cell is an abnormal battery cell according to the voltage drop sequence of the battery cell and the battery cell impedance" may include the following steps: S201, performing impedance consistency analysis on a batch of battery cells according to the battery cell impedance, and marking battery cells that do not meet the impedance consistency as abnormal battery cells.

[0054] Exemplarily, a batch of battery cells may include multiple battery cells used in the same model product / the same battery pack, or multiple battery cells of the same specification produced in the same batch; the number of battery cells in the batch of battery cells can be set as needed, and this application does not impose any restrictions.

[0055] Lithium-ion battery cell fractionation equipment can combine the cell impedance of each cell in a batch of cells to perform impedance consistency analysis on the batch of cells, and mark the cells that do not meet the impedance consistency as abnormal cells.

[0056] Impedance consistency refers to the closeness of the internal resistance of the same batch or group of cells. Impedance reflects the resistance of the cell to the current. The impedance of the cell can be measured by methods such as AC impedance method or DC discharge method.

[0057] Impedance consistency has a significant impact on the power output, charging efficiency and thermal management of the battery pack. Specifically: Inconsistent impedance will cause the battery pack to generate different heat during charging and discharging. Cells with larger impedance will generate more heat, which may cause local temperature rise, affect the performance and life of the battery, and even cause safety issues.

[0058] When discharging at high current, cells with smaller impedance can provide greater power output, while cells with larger impedance may not be able to meet the demand, thus affecting the performance of the entire battery pack.

[0059] Inconsistent impedance also affects the charging efficiency of the battery pack. Cells with larger internal resistance consume more energy when charging, resulting in longer charging time and lower charging efficiency.

[0060] The impedance consistency can be determined by setting a threshold, statistical analysis, trend analysis, etc. For example, a threshold range corresponding to impedance consistency can be set according to the type, specification, and application scenario of the battery. If the cell impedance of each cell in a battery pack falls within the threshold range, it can be considered that these cells have good impedance consistency.

[0061] In the embodiment of the present application, the battery cells that do not meet the impedance consistency are marked as abnormal battery cells.

[0062] S202: Performing consistency analysis of aging degrees on unmarked cells according to the voltage drop sequence of the cells, and marking cells that do not meet the aging degree consistency as abnormal cells.

[0063] Exemplarily, in the batch of cells, cells other than the abnormal cells marked in step S201 are unmarked cells. For each unmarked cell, the standard deviation is calculated according to each value included in the voltage drop sequence of the cell, and for the cell voltage drop sequence whose standard deviation exceeds the preset standard deviation threshold, it is confirmed that the corresponding cell does not meet the aging degree consistency, and the cell is marked as an abnormal cell.

[0064] In an embodiment of the present application, after performing an impedance consistency analysis on the battery cells, an aging degree consistency analysis is further performed on the battery cells that meet the impedance consistency analysis, so that battery cells with impedance that is too large or too small and a high degree of aging (i.e., a large voltage drop variation per unit time) are marked as abnormal batteries. The aging degree of the battery cells is analyzed when the impedance difference is small, thereby improving the accuracy of the aging degree consistency judgment.

[0065] Based on the above embodiments, Figure 3 As shown, in the above step S201, "performing impedance consistency analysis on a batch of battery cells according to the battery cell impedance, and marking the battery cells that do not meet the impedance consistency as abnormal battery cells" may include the following steps: S301, superimposing a first preset fluctuation threshold on the impedance mean of the batch of battery cells to determine a consistency screening range corresponding to the impedance.

[0066] Exemplarily, the cell impedance of each cell in the batch of cells is added together, and the obtained sum is divided by the total number of cells in the batch of cells to obtain the impedance mean of the batch of cells.

[0067] A first preset fluctuation threshold is superimposed on the impedance mean value, and the first preset fluctuation threshold includes a positive value and a negative value.

[0068] The impedance mean and the positive value of the first preset fluctuation threshold are added to obtain the upper limit value of the consistency screening range corresponding to the impedance; the impedance mean and the negative value of the first preset fluctuation threshold are added to obtain the lower limit value of the consistency screening range corresponding to the impedance.

[0069] Among them, the first preset fluctuation threshold can be set as needed and is not limited in this application.

[0070] In some embodiments, the first preset fluctuation threshold may be determined according to a standard deviation of impedance of a batch of battery cells.

[0071] For example, for a battery pack consisting of 10 cells, the measured impedances are 10mΩ, 11mΩ, 12mΩ, 10mΩ, 11mΩ, 12mΩ, 10mΩ, 11mΩ, 12mΩ, 11mΩ. The standard deviation is 0.82mΩ. Then the first preset fluctuation threshold is ±0.82, or ,N is a positive integer.

[0072] S302, marking the battery cells whose impedance is not within the consistency screening range corresponding to the impedance as abnormal battery cells.

[0073] It is determined in turn whether the cell impedance of each cell in the batch of cells is within the consistency screening range corresponding to the impedance. If so, it is not marked; if not, it is marked as an abnormal cell.

[0074] In the embodiment of the present application, the actual impedance mean value of the batch of cells is used as the basis, and the first preset fluctuation threshold is superimposed on the impedance mean value to determine the consistency screening range corresponding to the impedance. The impedance consistency screening is performed based on the range, which can avoid the situation where the consistency screening range and the actual impedance of the batch of cells deviate greatly, so that the screening range involved in the impedance consistency screening is effective. The batch of cells after screening can show good impedance consistency.

[0075] Based on the above embodiments, Figure 4 As shown, before "superimposing the first preset fluctuation threshold on the impedance mean of the batch of battery cells" in the above step S301, the abnormality detection method of the battery cell proposed in the embodiment of the present application may further include the following steps: S401, calculating impedance characteristic values ​​of the battery cells in batches, where the impedance characteristic values ​​represent impedance distribution of the battery cells in batches.

[0076] Exemplarily, the impedance characteristic values ​​of a batch of battery cells may include a mean value and a standard deviation.

[0077] S402, determining a cell whose cell impedance is discrete relative to the impedance characteristic value, and marking the cell as an abnormal cell.

[0078] Exemplarily, the difference between the cell impedance of a cell and the mean of the impedance characteristic value is calculated, and the absolute value of the difference is compared with the standard deviation. If the absolute value of the difference is greater than the standard deviation, the cell is marked as an abnormal cell; if the absolute value of the difference is less than or equal to the standard deviation, the cell is marked as an abnormal cell.

[0079] Correspondingly, in the above step S301, “adding the first preset fluctuation threshold to the impedance mean of the batch of battery cells” may include the following steps: S403, determining the impedance mean value corresponding to the unmarked cells in the batch of cells.

[0080] The abnormal cells marked in step S402 are removed from the batch of cells, and the impedance mean of the remaining cells is calculated, that is, the impedance mean corresponding to the unmarked cells.

[0081] S404: superimpose a first preset fluctuation threshold on the impedance mean value corresponding to the unmarked battery cell.

[0082] It should be noted that the specific implementation of this step can refer to the description of the specific implementation of step S301 in the above embodiment, which will not be repeated here.

[0083] In the embodiment of the present application, a first preset fluctuation threshold is superimposed on the impedance mean value corresponding to the unmarked battery cell to determine a consistency screening range corresponding to the impedance.

[0084] Before calculating the impedance mean of the batch of battery cells, this embodiment first screens the batch of battery cells to remove the battery cells that are discrete outside the overall distribution pattern of the batch of battery cells, and then calculates the impedance mean of the remaining battery cells as the impedance mean of the batch batteries, so as to improve the accuracy of the impedance mean, thereby improving the accuracy of the determined first fluctuation threshold.

[0085] Based on the above embodiments, the impedance test may include but is not limited to AC impedance test and DC impedance test. Figure 5 As shown, in the above step S102, "obtaining the voltage of the second type of battery cell at different test stages in the impedance test" may include the following steps: S501, performing the AC impedance test after the capacity division detection, and obtaining the cell voltage at the end of the AC impedance test as the second type cell voltage.

[0086] Exemplarily, the lithium-ion battery capacity fractionation equipment starts an AC impedance test after performing the capacity fractionation detection. The AC impedance test is to perform an impedance test on the battery cell using an alternating current impedance method (EIS).

[0087] By applying a small AC signal to the battery cell, the impedance response of the battery cell at different frequencies is measured.

[0088] At the end of the AC impedance test, the cell voltage is obtained as the second type cell voltage.

[0089] S502, performing a DC impedance test after the AC impedance test, and obtaining the cell voltage at the end of each discharge stage during the DC impedance test as the second type of cell voltage; the DC impedance test includes performing staged discharge on the cell with different discharge currents and discharge durations.

[0090] Exemplarily, the DC impedance test is started after the AC impedance test is finished. The DC impedance test is a resistance test performed by a DC discharge method.

[0091] For example, after the cell is formed at high temperature, the lithium-ion battery capacity separation equipment can carry out cell capacity separation detection at the target temperature (the target temperature can be set as needed, such as 45±5℃; 25±5℃), and record the cell voltage V1 at the initial moment of the cell shelf detection as the first type of cell voltage. And obtain and record the cell voltage V2 at the end of the capacity separation, also as the first type of cell voltage.

[0092] The power of the cell at the beginning of the capacity division is SOC1, and the power at the end of the capacity division is SOC2. The lithium-ion battery capacity division equipment carries out EIS (Electrochemical Impedance Spectroscopy) detection (i.e. AC impedance test) at SOC2 power. The EIS detection process, frequency range, test time and other parameters can be pre-set. The ohmic internal resistance, SEI film impedance and charge transfer impedance of the cell can be obtained through AC impedance test. After completing the AC impedance test, record the cell voltage V2 when the AC impedance test is completed as the second type of cell voltage; calculate the time interval T3 from the battery voltage V1 to V2, and then calculate K1=(V1-V2) / T3.

[0093] After completing the AC impedance test, a DC impedance test (DCR) is performed. In the DC impedance test, the battery cell can be discharged with a current I1 for the first stage, and the discharge time is t1 (for example, I1≤0.2C, C is the rate; t1=10s); and then the battery cell is discharged with a current I2 for the second stage, and the discharge time is t2 (for example, I2=1C, t2=1s). Record the battery cell voltage V3 at the end of the first stage discharge and the battery cell voltage V4 at the end of the second stage discharge. Calculate the time interval T4 from the battery voltage V1 to V3, and calculate K2=(V1-V3) / T4.

[0094] In the process of capacity division and impedance testing of battery cells, the embodiment of the present application collects battery cell voltages at different times, so that the battery cell voltage can be obtained while obtaining the battery cell impedance, and the voltage drop of the battery cell per second at different times is determined according to the battery cell voltages collected at different times, so as to analyze whether the voltage drop per second of the battery cell shows abnormal fluctuation after experiencing application processes such as capacity division, AC charging and DC discharging. In this way, the aging degree of the battery cell is evaluated. Compared with the conventional open circuit voltage detection time of 48-72h, the present application shortens the abnormal detection to a few hours, thereby reducing the time consumption of abnormal detection.

[0095] On the basis of the above embodiment, the battery cell may be further detected for abnormality, such as Figure 6 As shown, the following steps may be included: S601, calculating the sum of the cell ohmic internal resistance, membrane impedance and charge transfer impedance of the cell as the total AC impedance of the cell.

[0096] For example, the ohmic internal resistance, SEI film impedance and charge transfer impedance of the battery cell can be obtained through AC impedance testing, and the sum of the three types of impedance is taken as the total AC impedance value of the battery cell.

[0097] S602, calculating the ratio of the total AC impedance of the battery cell to the DC internal resistance.

[0098] S603, determining whether the ratio is within a preset ratio range, and if not, marking the battery cell as an abnormal battery cell.

[0099] The DC internal resistance of the battery cell can be obtained through the DC impedance test. The ratio of the total AC impedance value and the DC internal resistance of the same battery cell is calculated; it is determined whether the ratio is within the preset ratio range. If so, there is no need to mark the battery cell. If not, the battery cell is marked as an abnormal battery cell.

[0100] The preset ratio range may be determined according to the second preset fluctuation threshold value and the ratio of the total AC impedance value to the DC internal resistance value measured when the battery cell is in the maximum charge state.

[0101] For example, when the SOC is 100%, the battery cell is sequentially subjected to an AC impedance test and a DC impedance test, and then the battery cell is charged and discharged until the charge of the battery cell reaches SOC2, and the battery cell is subjected to one or more AC impedance tests and DC impedance tests at SOC2.

[0102] The battery cell is subjected to the first AC impedance test when the SOC is 100%, and the total AC impedance value is Reis,1, and the DC internal resistance is Rdcr,1. After the battery cell is subjected to capacity detection, the battery cell power drops to SOC 70%. The battery cell is subjected to the second AC impedance test when the SOC is 70%, and the total AC impedance test value is Reis,2. The battery cell is subjected to the second DC impedance test, and the DC internal resistance is Rdcr,2.

[0103] A second preset fluctuation threshold is superimposed on Reis,1 / Rdcr,1 to obtain a preset ratio range, wherein the second preset fluctuation threshold includes positive and negative values ​​with the same absolute value. The preset ratio range is used to screen the Reis,2 / Rdcr,2 values ​​of multiple battery cells.

[0104] The embodiment of the present application analyzes the ratio of the total AC impedance to the DC internal resistance of the battery cell after it has undergone application processes such as charging and discharging, and performs further abnormality detection on the battery cell based on the deviation degree compared to the maximum charge state, thereby improving the effect of abnormality detection.

[0105] To implement the above embodiment, the present application provides a battery cell abnormality detection device, such as Figure 7 As shown, the device 700 includes: A first acquisition module 701 is used to acquire the voltage of the first type of battery cells when the capacity division detection starts and the acquisition time of the voltage of the first type of battery cells; A second acquisition module 702 is used to acquire the voltage of the second type of battery cell and the acquisition time of the voltage of the second type of battery cell at different test stages in the impedance test, wherein the impedance test is started after the capacity division detection is completed; A third acquisition module 703 is used to obtain the cell impedance obtained by the impedance test; A calculation module 704, configured to calculate a voltage drop sequence of the battery cell according to the voltage of the first type of battery cell, the voltage of the second type of battery cell, the collection time of the voltage of the first type of battery cell, and the collection time of the voltage of the second type of battery cell, wherein the voltage drop sequence includes values ​​of the voltage drop at different times within a unit time; The abnormality detection module 705 is used to determine whether the battery cell is an abnormal battery cell according to the voltage drop sequence of the battery cell and the battery cell impedance.

[0106] In one embodiment, the abnormality detection module is used to: perform impedance consistency analysis on a batch of battery cells based on the battery cell impedance, and mark the battery cells that do not meet the impedance consistency as abnormal battery cells; perform aging consistency analysis on unmarked battery cells based on the voltage drop sequence of the battery cells, and mark the battery cells that do not meet the aging consistency as abnormal battery cells.

[0107] In one embodiment, the abnormality detection module is used to: superimpose a first preset fluctuation threshold on the impedance mean of the batch of battery cells to determine a consistency screening range corresponding to the impedance; and mark the battery cells whose impedance is not within the consistency screening range corresponding to the impedance as abnormal battery cells.

[0108] In one embodiment, the abnormality detection module is used to: calculate the impedance characteristic value of the batch of battery cells, the characteristic value characterizing the impedance distribution of the batch of battery cells; determine the battery cells whose impedance is discrete relative to the characteristic value, and mark the battery cells as abnormal batteries; determine the impedance mean value corresponding to the unmarked battery cells in the batch of battery cells; and superimpose the first preset fluctuation threshold on the impedance mean value corresponding to the unmarked battery cells.

[0109] In one embodiment, the impedance test includes an AC impedance test and a DC impedance test, and the second acquisition module is used to: perform the AC impedance test after the capacity division detection, and obtain the battery cell voltage at the end of the AC impedance test as the second type of battery cell voltage; perform the DC impedance test after the AC impedance test, and obtain the battery cell voltage at the end of each discharge stage during the DC impedance test as the second type of battery cell voltage; the DC impedance test includes staged discharge of the battery cell with different discharge currents and discharge durations.

[0110] In one embodiment, the battery cell impedance includes the AC impedance obtained by the AC impedance test and the DC internal resistance obtained by the DC impedance test, and the AC impedance includes the battery cell ohmic internal resistance, the membrane impedance of the solid electrolyte interface membrane and the charge transfer impedance; the abnormality detection module is also used to: calculate the sum of the battery cell ohmic internal resistance, the membrane impedance and the charge transfer impedance of the battery cell as the total AC impedance of the battery cell; calculate the ratio of the total AC impedance of the battery cell to the DC internal resistance; determine whether the ratio is within a preset ratio range, and if not, mark the battery cell as an abnormal battery cell.

[0111] In one embodiment, the preset ratio range is determined according to a second preset fluctuation threshold value and a ratio of a total AC impedance value to a DC internal resistance value measured when the battery cell is in a maximum state of charge.

[0112] In summary, the abnormality detection device for battery cells proposed in the embodiments of the present application adds an impedance test after performing capacity division detection on the battery cells, and obtains the first type of battery cell voltage and the collection time of the first type of battery cell voltage at the beginning of the capacity division detection, as well as obtains the second type of battery cell voltage and the collection time of the second type of battery cell voltage at different test stages of the impedance test, and obtains the battery cell impedance obtained by the impedance test; then, according to the first type of battery cell voltage, the collection time of the first type of battery cell voltage, each second type of battery cell voltage and the collection time of the second type of battery cell voltage, the voltage drop sequence of the battery cell is determined, and the voltage drop sequence includes the values ​​of the voltage drop per unit time at different times; finally, according to the voltage drop sequence of the battery cell and the battery cell impedance, it is determined whether the battery cell is an abnormal battery cell. The present application performs an impedance test after the capacity division detection to test the impedance of the battery cell in a stable state and improve the accuracy of the impedance test; the voltage of the first type of battery cell is the initial voltage of the battery cell when the capacity division detection starts, and the voltage of the second type of battery cell includes the voltage of the battery cell at different times after discharge. The stability of the voltage drop of the battery cell per unit time can be determined based on the voltage of the first type of battery cell and the voltage of the second type of battery cell. The present application performs abnormality detection on the battery cell in combination with the impedance of the battery cell and the stability of the voltage drop per unit time. Compared with judging whether the battery cell has an abnormality by observing the changing trend of the open circuit voltage for a long time, the present application takes less time.

[0113] In one embodiment, a lithium-ion battery capacity conversion device is provided, such as Figure 8 As shown, the lithium-ion battery capacity conversion device 800 may include a battery cell abnormality detection module 801; The battery cell abnormality detection module 801 is used to execute the steps of the battery cell abnormality detection method shown in any of the above embodiments.

[0114] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored, and when the computer program is executed by a processor, the method for detecting abnormality of a battery cell in any of the above embodiments is implemented. Alternatively, when the computer program is executed by a processor, the functions of each module / unit in the embodiment of the abnormality detection device for a battery cell are implemented, and to avoid repetition, they are not described here.

[0115] Those of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application may include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0116] Those skilled in the art can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0117] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A method for detecting abnormality of a battery cell, characterized in that: The method comprises: Acquire the voltage of the first type of battery cells when the capacity division detection starts and the acquisition time of the voltage of the first type of battery cells; Acquire the voltage of the second type of battery cell and the acquisition time of the voltage of the second type of battery cell at different test stages in the impedance test, wherein the impedance test is started after the capacity division detection is completed; Obtaining the cell impedance obtained by the impedance test; Calculate a voltage drop sequence of the battery cell according to the voltage of the first type of battery cell, the voltage of the second type of battery cell, the collection time of the voltage of the first type of battery cell, and the collection time of the voltage of the second type of battery cell, wherein the voltage drop sequence includes values ​​of the voltage drop at different times within a unit time; Whether the battery cell is an abnormal battery cell is determined according to the voltage drop sequence of the battery cell and the battery cell impedance.

2. The method according to claim 1, characterized in that The determining whether the battery cell is an abnormal battery cell according to the voltage drop sequence of the battery cell and the battery cell impedance includes: According to the cell impedance, an impedance consistency analysis is performed on the batch of cells, and cells that do not meet the impedance consistency are marked as abnormal cells; According to the voltage drop sequence of the battery cells, the consistency analysis of the aging degree of the unmarked battery cells is performed, and the battery cells that do not meet the aging degree consistency are marked as abnormal battery cells.

3. The method according to claim 2, characterized in that The step of performing impedance consistency analysis on the batch of cells according to the cell impedance and marking the cells that do not meet the impedance consistency as abnormal cells includes: Superimposing a first preset fluctuation threshold on the impedance mean value of the batch of battery cells to determine a consistency screening range corresponding to the impedance; The cell whose cell impedance is not within the consistency screening range corresponding to the impedance is marked as an abnormal cell.

4. The method according to claim 3, characterized in that Before superimposing the first preset fluctuation threshold on the impedance mean value of the batch of battery cells, the method further includes: Calculating impedance characteristic values ​​of the batch of battery cells, wherein the impedance characteristic values ​​represent impedance distribution of the batch of battery cells; Determine a battery cell whose impedance is discrete relative to the impedance characteristic value, and mark the battery cell as an abnormal battery cell; The step of superimposing a first preset fluctuation threshold on the impedance mean value of the batch of battery cells comprises: Determining an impedance mean value corresponding to unmarked cells in the batch of cells; The first preset fluctuation threshold is superimposed on the impedance mean value corresponding to the unmarked battery cell.

5. The method according to claim 1, characterized in that The impedance test includes an AC impedance test and a DC impedance test, and obtaining the voltage of the second type of battery cell at different test stages in the impedance test includes: Performing the AC impedance test after the capacity division test, and acquiring the cell voltage at the end of the AC impedance test as the second type of cell voltage; Performing the DC impedance test after the AC impedance test, and obtaining the cell voltage at the end of each discharge stage during the DC impedance test as the second type of cell voltage; The DC impedance test includes discharging the battery cell in stages with different discharge currents and discharge durations.

6. The method according to any one of claims 1 to 5, characterized in that: The cell impedance includes an AC impedance obtained by an AC impedance test and a DC internal resistance obtained by a DC impedance test, and the AC impedance includes an ohmic internal resistance of the cell, a membrane impedance of a solid electrolyte interface membrane, and a charge transfer impedance; the method further includes: Calculating the sum of the cell ohmic internal resistance, the membrane impedance and the charge transfer impedance of the cell as the total AC impedance of the cell; Calculating the ratio of the total AC impedance of the battery cell to the DC internal resistance; It is determined whether the ratio is within a preset ratio range, and if not, the battery cell is marked as an abnormal battery cell.

7. The method according to claim 6, characterized in that The preset ratio range is determined according to the second preset fluctuation threshold value and the ratio of the total AC impedance value to the DC internal resistance value measured when the battery cell is in the maximum charge state.

8. A battery cell abnormality detection device, characterized in that: The device comprises: A first acquisition module, used for acquiring the voltage of the first type of battery cells when the capacity division detection starts and the acquisition time of the voltage of the first type of battery cells; A second acquisition module is used to obtain the voltage of the second type of battery cell and the acquisition time of the voltage of the second type of battery cell at different test stages in the impedance test, wherein the impedance test is started after the capacity division detection is completed; A third acquisition module is used to obtain the cell impedance obtained by the impedance test; A calculation module, used for calculating a voltage drop sequence of the battery cell according to the voltage of the first type of battery cell, the voltage of the second type of battery cell, the collection time of the voltage of the first type of battery cell and the collection time of the voltage of the second type of battery cell, wherein the voltage drop sequence includes values ​​of the voltage drop at different times within a unit time; The abnormality detection module is used to determine whether the battery cell is an abnormal battery cell according to the voltage drop sequence of the battery cell and the battery cell impedance.

9. A lithium-ion battery capacity conversion device, characterized in that: The device includes a battery cell abnormality detection module; The battery cell abnormality detection module is used to execute the steps of the battery cell abnormality detection method as described in any one of claims 1 to 7 above.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the abnormality detection method for a battery cell as claimed in any one of claims 1 to 7 is implemented.

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