Screening method for battery self-discharge

Abstract

The invention discloses a battery self-discharge screening method. The method comprises the following steps: respectively acquiring compensation currents required for maintaining voltages of a plurality of single batteries at preset voltages; and according to the plurality of compensation currents, determining outlier single batteries, and taking the outlier single batteries as single batteries with abnormal self-discharge. The compensation current itself is a direct reaction of the self-discharge degree, so that the battery monomer of which the self-discharge degree is greatly different from the self-discharge degree of other battery monomers can be determined according to the magnitude of the compensation current of each battery monomer, and the battery monomer is used as the battery monomer of which the self-discharge is abnormal; according to the invention, the single battery with abnormal self-discharge can be determined in a short time, the cycle of battery self-discharge detection is shortened, and the detection efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of battery self-discharge detection technology, and in particular to a method for screening battery self-discharge. Background Technology

[0002] Lithium-ion batteries commonly exhibit self-discharge during manufacturing and storage due to the instability of their internal chemical systems. This self-discharge stems from side reactions at the electrode-electrolyte interface (such as SEI film decomposition and transition metal dissolution), micro-short circuits (separator defects, metal impurity punctures), and loss of active lithium. Abnormal self-discharge leads to a continuous decline in the battery's state of charge (SOC), accelerating capacity decay (with an annual decay rate exceeding 20%), and causing voltage inconsistencies between individual cells within the battery pack, potentially even triggering thermal runaway.

[0003] Traditional self-discharge screening methods include the open-circuit voltage method and the capacity retention rate method. The traditional open-circuit voltage method involves charging the battery to 100% SOC and letting it rest for 7-30 days. During this resting period, the open-circuit voltage is measured at intervals, and the K value is calculated to further identify batteries with abnormal self-discharge. The open-circuit voltage method has a relatively long measurement cycle. The capacity retention rate method involves charging the battery to the cutoff voltage and letting it rest for 7-30 days, recording the capacity before and after charging, and obtaining the capacity retention rate. This allows for the screening of batteries with high self-discharge. This method also suffers from a relatively long screening cycle. Summary of the Invention

[0004] This invention provides a method for screening battery self-discharge to solve the problem of long detection cycles when detecting battery self-discharge.

[0005] According to one aspect of the present invention, a method for screening battery self-discharge is provided, comprising:

[0006] The compensation current required to maintain the voltage of each of the multiple battery cells at a preset voltage is obtained separately.

[0007] The outlier battery cells are identified based on the multiple compensation currents, and these outlier battery cells are identified as battery cells with self-discharge abnormalities.

[0008] Optionally, determining the outlier battery cells based on the plurality of compensation currents includes:

[0009] The compensation current curve of each battery cell is generated based on the compensation current of each battery cell at each sampling time within a preset time period.

[0010] The outlier battery cells were identified based on the compensation current curves described above.

[0011] Optionally, determining the outlier battery cells based on each of the compensation current curves includes:

[0012] Obtain the corresponding compensation current for each of the aforementioned compensation current curves at the same sampling time;

[0013] Calculate the average compensation current of multiple compensation currents at the same sampling time;

[0014] A total current mean curve is generated based on the multiple compensation current mean values;

[0015] Calculate the difference between each of the compensation current curves and the total average current curve; the difference is characterized by the root mean square error or mean absolute error of the difference between the compensation current and the average compensation current at all sampling times within the preset time period.

[0016] The compensation current curve whose difference from the average total current curve is greater than a preset value is identified as an outlier compensation current curve.

[0017] The battery cell corresponding to the outlier compensation current curve is considered the outlier battery cell.

[0018] Optionally, determining the outlier battery cells based on the plurality of compensation currents includes:

[0019] For each battery cell, the average compensation current of each battery cell is generated based on the compensation current at each sampling time within a preset time period.

[0020] The average total compensation current is generated based on the average compensation current of each individual battery cell.

[0021] Battery cells whose average compensation current deviates from the average total compensation current by a greater than a deviation threshold are considered outlier battery cells.

[0022] Optionally, obtaining the compensation current required to maintain the voltage of each of the multiple battery cells at a preset voltage includes:

[0023] Current compensation is performed on the battery cells whose real-time voltage is lower than the preset voltage;

[0024] Obtain the compensation current of each battery cell at various sampling times within a preset time period.

[0025] Optionally, obtaining the compensation current of each battery cell at various sampling times within a preset time period includes:

[0026] Obtain the voltage of each of the battery cells at each sampling time within the preset time period;

[0027] The compensation current for the battery cell is generated based on the voltage of the battery cell, the preset voltage, and the resistance of the battery cell.

[0028] Optionally, before obtaining the compensation current required to maintain the voltage of each of the plurality of battery cells at a preset voltage, the method further includes:

[0029] Each of the battery cells is charged to the preset voltage under the same conditions;

[0030] Obtain the real-time voltage of each of the battery cells.

[0031] Optionally, after each of the battery cells has been charged to the preset voltage, the step of obtaining the real-time voltage of each battery cell is started after a first set time period of rest.

[0032] Optionally, after each of the battery cells has been charged to the preset voltage and left to stand for a first set time, the method further includes:

[0033] The step of acquiring the voltage of each battery cell at each sampling time within the preset time period is executed at a second predetermined time interval. Optionally, the battery self-discharge screening method further includes:

[0034] At each sampling time, the temperature of each of the battery cells is acquired;

[0035] When the temperature of the battery cell is greater than the upper temperature limit or less than the lower temperature limit, the acquisition of the compensation current for the battery cell is stopped.

[0036] In this embodiment, the magnitude of the compensation current of each battery cell is detected, and outlier battery cells are screened based on the magnitude of their compensation currents. The compensation current itself is a direct reflection of the self-discharge level; therefore, battery cells with significantly different self-discharge levels from other battery cells can be identified based on their compensation current magnitude and classified as having abnormal self-discharge. This allows for the identification of battery cells with abnormal self-discharge in a shorter time, shortening the battery self-discharge detection cycle and improving detection efficiency.

[0037] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 A flowchart illustrating a battery self-discharge screening method provided in an embodiment of the present invention;

[0040] Figure 2 A flowchart of another battery self-discharge screening method provided in an embodiment of the present invention;

[0041] Figure 3 A schematic diagram of a compensation current curve provided in an embodiment of the present invention;

[0042] Figure 4 A flowchart of another battery self-discharge screening method provided in an embodiment of the present invention;

[0043] Figure 5 A flowchart of another battery self-discharge screening method provided in an embodiment of the present invention;

[0044] Figure 6 A flowchart of another battery self-discharge screening method provided in an embodiment of the present invention. Detailed Implementation

[0045] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0046] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0047] Figure 1 A flowchart of a battery self-discharge screening method provided in an embodiment of the present invention is shown below. Figure 1 The screening method for battery self-discharge includes:

[0048] S110: Obtain the compensation current required to maintain the voltage of each of the multiple battery cells at a preset voltage.

[0049] A battery consists of multiple individual cells, which are connected in series and / or parallel to form a battery, in order to meet the specific requirements of different applications for voltage, capacity, and power. Specifically, when multiple individual cells are used to form a battery, the positive and negative terminals of each individual cell are connected in series to form a battery; alternatively, the positive terminals of all individual cells are connected together and all the negative terminals are connected together, and the individual cells are connected in parallel to form a battery; or, several individual cells are first connected in parallel to form a group, and then multiple such groups are connected in series to form a battery.

[0050] The sampling frequency can be set according to requirements, such as 1 second / sample. At the set sampling interval, the compensation current of each battery cell is acquired at a fixed frequency. That is, at each sampling moment, the compensation current required to maintain the voltage of each battery cell at a preset voltage is acquired. In an optional method, the current required for each battery cell to maintain the preset voltage is used as the compensation current. Optionally, the preset voltage can be any voltage value within the range of 2.5V to 4.3V.

[0051] S120: Identify outlier battery cells based on multiple compensation currents and treat them as cells with abnormal self-discharge. Outlier battery cells are used to characterize battery cells whose self-discharge level differs from that of other battery cells by a threshold value.

[0052] Outlier battery cells are identified based on the compensation current of each individual cell at at least one sampling time. Since the battery cells are similar in terms of usage time, temperature, and other factors, their self-discharge levels are generally the same. In one optional implementation, at a given sampling time, the average compensation current of all battery cells is calculated. Battery cells whose compensation current differs from this average by a threshold value are marked as undetermined cells. This process is repeated for each sampling time. If a battery cell is identified as an undetermined cell in 100 consecutive sampling times (e.g., a predetermined number of times), it is identified as an outlier, thus identifying cells with abnormal self-discharge. After identifying cells with abnormal self-discharge, the battery can be repaired or scrapped by notifying personnel to remove it, or by addressing an issue where the number of cells with abnormal self-discharge exceeds a certain threshold.

[0053] In this embodiment, the magnitude of the compensation current of each battery cell is detected in real time, and outlier battery cells are screened out based on the magnitude of multiple compensation currents. The compensation current itself is a direct reflection of the self-discharge level. Therefore, battery cells with significantly different self-discharge levels from other battery cells can be identified based on the magnitude of their compensation currents, and these are identified as battery cells with abnormal self-discharge. This allows for the identification of battery cells with abnormal self-discharge in a shorter time, shortening the battery self-discharge detection cycle and improving detection efficiency.

[0054] Figure 2 A flowchart of another battery self-discharge screening method provided in an embodiment of the present invention is shown below. Figure 2 The screening method for battery self-discharge includes:

[0055] S111: Obtain the compensation current required to maintain the voltage of each of the multiple battery cells at a preset voltage.

[0056] Optionally, S111 may further include:

[0057] Step a1: Perform current compensation on battery cells whose real-time voltage is lower than the preset voltage.

[0058] As the battery cells are left to stand, their voltage will gradually decrease due to self-discharge. The battery cells that have dropped below the preset voltage are charged to compensate for the current and raise their voltage.

[0059] Step a2: Obtain the compensation current of each battery cell at each sampling time within a preset time period.

[0060] Further step a2 includes:

[0061] Step a21: Obtain the voltage of each battery cell at each sampling time within a preset time period. The voltage of the battery cell can be obtained through a voltage sensor.

[0062] Step a22: Generate the compensation current for the battery cell based on the voltage of the battery cell, the preset voltage, and the resistance of the battery cell.

[0063] The compensation current for a battery cell is obtained by dividing the absolute value of the difference between the voltage of the individual battery cell and the preset voltage by the resistance of the individual battery cell. The resistance of the individual battery cell can be predetermined and determined experimentally; minor changes in resistance are ignored in subsequent measurements. For a given sampling time, the compensation current for that individual battery cell is generated based on its voltage, the preset voltage, and its resistance, thus obtaining the compensation current for each individual battery cell.

[0064] S121: Generate the compensation current curve for each battery cell based on the compensation current at each sampling time within a preset time period.

[0065] For a single battery cell, a compensation current curve for that battery cell is generated based on the compensation current at various sampling times within a preset time period. This method is used to generate the compensation current curve for each battery cell within the preset time period. The preset time period can be set between 20 and 50 minutes. In this embodiment, a preset time period of 20 minutes is exemplified. Taking a sampling frequency of 1 second / time as an example, the preset time period includes 1200 sampling times, and each battery cell corresponds to 1200 compensation currents. Taking a specific battery cell as an example, adjacent sampling points of that battery cell are connected by straight lines to form the compensation current curve corresponding to that battery cell. In other embodiments, a data function f(t) can be found such that the curve of the function is closest to the 1200 data points corresponding to the battery cell. The curve of this function f(t) represents the compensation current curve of the battery cell. In this embodiment, the method for generating compensation current curves based on multiple sampling points is not specifically limited; any feasible method in related technologies can be used. In the compensation current curve, the horizontal axis represents time (in seconds), and the vertical axis represents compensation current (in amperes).

[0066] The compensation current curve for each battery cell within a preset time period is generated according to the above method.

[0067] S131: Identify the outlier battery cells based on the various compensation current curves, and treat the outlier battery cells as battery cells with self-discharge abnormalities.

[0068] Because individual battery cells self-discharge, their voltage drops slowly. To maintain this voltage at a preset level, the testing equipment applies a small compensation current to "make up" for the energy lost due to self-discharge. Therefore, the magnitude of the compensation current can characterize the magnitude of the self-discharge current. Consequently, the height of the compensation current curve directly represents the rate of self-discharge.

[0069] The compensation current curves of each battery cell within a preset time period can be plotted on the same coordinate system to identify outlier compensation current curves, and the battery cells corresponding to these outlier curves are designated as outlier battery cells. Outlier compensation current curves are those whose shape and characteristics are significantly different from most compensation current curves. Figure 3 This is a schematic diagram of a compensation current curve provided in an embodiment of the present invention, for reference. Figure 3 , Figure 3 Taking a battery consisting of four cells as an example, the black curve is the compensation current curve of cell 1, the red curve is the compensation current curve of cell 2, the blue curve is the compensation current curve of cell 3, and the yellow curve is the compensation current curve of cell 4. Figure 3 The horizontal axis represents time, and the vertical axis represents the compensation current. Figure 3 It can be seen that the compensation current curve of battery cell 4 is obviously out of the loop, so the compensation current curve of battery cell 4 is regarded as the out-of-loop compensation current curve.

[0070] In this embodiment, the outlier compensation current curves are more intuitively determined by plotting the compensation current curves of each battery cell on the same coordinate system. Then, the outlier battery cell is determined based on the outlier compensation current curves. The whole process is more intuitive and efficient.

[0071] Figure 4 A flowchart of another battery self-discharge screening method provided in an embodiment of the present invention is shown below. Figure 4 The screening method for battery self-discharge includes:

[0072] S112: Obtain the compensation current required to maintain the voltage of each of the multiple battery cells at a preset voltage.

[0073] S122: Generate a compensation current curve based on the compensation current of each battery cell at various sampling times within a preset time period. For a single battery cell, generate a compensation current curve based on the compensation current of that battery cell at various sampling times within a preset time period.

[0074] S132: Obtain the corresponding compensation current for each compensation current curve at the same sampling time.

[0075] For example, within a preset time period including n sampling times t1, t2, t3, ..., tn, the compensation current of each battery cell at time t1, t2, t3, and so on, is obtained based on the compensation current curves corresponding to each battery cell. Specifically, obtaining the compensation current of each battery cell at time t1 involves obtaining the compensation current of the first battery cell at time t1 based on its compensation current curve, obtaining the compensation current of the second battery cell at time t1 based on its compensation current curve, obtaining the compensation current of the third battery cell at time t1 based on its compensation current curve, and so on, for the same sampling times t2 and others.

[0076] S142: Calculate the average compensation current of multiple compensation currents at the same sampling time.

[0077] Taking t1 as an example, the average compensation current at t1 is obtained by summing the compensation currents of each battery cell and then dividing by the number of battery cells. The calculation method for the average compensation current at other sampling times is similar and will not be repeated here. A corresponding average compensation current is calculated for each sampling time.

[0078] S152: Generate a total current mean curve based on multiple compensation current mean values. Further, generate a total current mean curve based on the respective compensation current mean values ​​at each sampling time.

[0079] A data point (t1, I) is formed by a sampling time and the average compensation current at that sampling time. b1 (t2, I) b2 ), ..., (tn, I bn Taking a preset time period including n sampling times as an example, the average curve of total current is generated based on the n data points.

[0080] S162: Calculate the difference between each compensation current curve and the total average current curve. The difference is characterized by the root mean square error or mean absolute error of the difference between the compensation current and the average compensation current at all sampling times within a preset time period.

[0081] If the difference is represented by the root mean square error, then taking the first compensation current curve as an example, the difference D1 between this compensation current curve and the total current mean curve can be: ;in, This represents the compensation current of the first compensation current curve at sampling time ti. Let be the average compensation current corresponding to the total current mean curve at sampling time ti. The difference between each compensation current curve and the total current mean curve can be obtained from the above formula. The mean absolute error can be calculated similarly to the above principle and will not be elaborated further here.

[0082] S172: The compensation current curve whose difference from the average total current curve is greater than a preset value is identified as an outlier compensation current curve.

[0083] The larger the difference between the compensation current curve and the average total current curve, the greater the difference between the battery cell corresponding to the compensation current curve and the average level of all battery cells, and the more likely it is to be an outlier battery cell. Therefore, compensation current curves with a difference greater than a preset value from the average total current curve are identified as outlier compensation current curves. The preset value can be set by the user and can be understood as the minimum difference between the two curves when the difference between them can no longer be ignored.

[0084] S182: The battery cell corresponding to the outlier compensation current curve is regarded as the outlier battery cell, and the outlier battery cell is regarded as the battery cell with abnormal self-discharge.

[0085] In other embodiments, Figure 5 A flowchart of another battery self-discharge screening method provided in an embodiment of the present invention is shown below. Figure 5 The method includes:

[0086] S113: Obtain the compensation current required to maintain the voltage of each of the multiple battery cells at a preset voltage.

[0087] S123: For each battery cell, generate the average compensation current value corresponding to each battery cell based on the compensation current at each sampling time within a preset time period.

[0088] Taking battery cell 1 as an example, for instance, if the preset duration is 20 minutes and the sampling frequency is 1 second / time, then the compensation current obtained by battery cell 1 at 1200 sampling times within 20 minutes is added together and divided by 1200 to obtain the average current of battery cell 1. For a single battery cell, the average compensation current is generated based on the compensation current of the battery cell at each sampling time within the preset duration.

[0089] S133: Generate the average total compensation current based on the average compensation current of each individual battery cell.

[0090] Taking a battery consisting of 20 individual cells as an example, the average compensation current of each of the 20 individual cells is added together and then divided by 20 to obtain the average total compensation current.

[0091] S143: The battery cells corresponding to the average compensation current values ​​where the deviation between the average compensation current value and the average total compensation current value is greater than the deviation threshold are identified as outlier battery cells, and these outlier battery cells are identified as battery cells with abnormal self-discharge.

[0092] The deviation threshold can be set according to different types of battery cells. If the average compensation current of a certain battery cell deviates significantly from the average compensation current of the total compensation current, it indicates that the self-discharge current of that battery cell differs significantly from the self-discharge current of most battery cells, and can be considered as having an abnormal self-discharge.

[0093] Figure 6 A flowchart of another battery self-discharge screening method provided in an embodiment of the present invention is shown below. Figure 6 The method includes:

[0094] S114: Charge each individual battery cell to a preset voltage under the same conditions.

[0095] Each battery cell is charged to a preset voltage under identical charging conditions, such as the same temperature, humidity, location, charging parameters, and interference factors. The preset voltage can be the voltage of the battery cell when it reaches 100% SOC.

[0096] Preferably, each battery cell is charged synchronously under the same conditions, or in other embodiments, each battery cell is charged sequentially to a preset voltage under the same conditions.

[0097] S124: After each battery cell is charged to the preset voltage, let it stand for a first set time.

[0098] Because the state of charge within a battery cell is unstable in the initial stage after charging is completed, the measured voltage error is relatively large. Therefore, after charging is completed, each battery cell is left to stand for a period of time, such as 5 hours as the first set time, before executing S134.

[0099] S134: Obtain the real-time voltage of each individual battery cell.

[0100] The battery cells are charged to a fixed, relatively high SOC (e.g., 100%), and then float-charged at this voltage. During this process, the battery cells will undergo self-discharge, therefore, it is necessary to monitor the voltage of each individual cell in real time. This real-time voltage can be obtained through a voltage acquisition module, such as a corresponding voltage sensor.

[0101] S144: Perform current compensation for battery cells whose real-time voltage is lower than the preset voltage.

[0102] S154: Second interval.

[0103] When the voltage of a battery cell drops, the battery cell exhibits self-discharge. In the initial stage of self-discharge, due to the electrochemical relaxation process inside the battery cell, the voltage fluctuates greatly, and the data is unreliable. Therefore, it is necessary to wait for a second set time interval, such as 2 hours, until the self-discharge of the battery cell enters a steady state before determining the magnitude of the corresponding compensation current by acquiring the voltage change of the battery cell, so as to ensure the accuracy of the determined compensation current.

[0104] S164: Obtain the voltage of each battery cell at each sampling time within a preset time period.

[0105] S174: Generates the compensation current for the battery cell based on the voltage of the battery cell, the preset voltage, and the resistance of the battery cell.

[0106] S184: Identify outlier battery cells based on multiple compensation currents and treat them as cells with self-discharge abnormalities. For details on the implementation of S184, refer to S120, S121-S131, or S122-182; further details will not be provided here.

[0107] In this embodiment, multiple battery cells are charged to a preset voltage under the same conditions; the voltage across each battery cell is detected in real time; when a decrease in the voltage of a battery cell is detected, the compensation current required to maintain the preset voltage of the open circuit voltage of the battery cell is calculated, and then the outlier battery cell, that is, the battery cell with abnormal self-discharge, is determined based on multiple compensation currents.

[0108] The battery self-discharge screening method provided in this embodiment starts sampling the individual battery cells after they enter the self-discharge steady state period to obtain the compensation current of each individual battery cell. This ensures that the obtained compensation current can accurately characterize the degree of self-discharge and improves the detection accuracy.

[0109] Optionally, the screening method for battery self-discharge also includes:

[0110] At each sampling time, the temperature of each battery cell is acquired; when the temperature of a battery cell is greater than the upper temperature limit or less than the lower temperature limit, the acquisition of the compensation current of the battery cell is stopped.

[0111] A temperature sensor can be set for each battery cell to obtain the temperature of the corresponding battery cell. When the temperature of a battery cell is outside the normal temperature range (i.e., above the upper temperature limit or below the lower temperature limit), it indicates that the temperature of the battery cell is abnormal, such as ultra-high temperature or ultra-low temperature. At this time, the obtained compensation current and other data are inaccurate, and it is impossible to determine whether there is an abnormal self-discharge of the battery cell. Therefore, the acquisition of compensation current for the battery cell is stopped.

[0112] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this invention can be achieved, and this is not limited herein.

[0113] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method of screening for self-discharge of a battery, characterized by, The method comprises the following steps: obtaining compensation currents required for maintaining the voltages of a plurality of battery cells at preset voltages respectively; determining an outlier battery cell from the plurality of compensation currents, and regarding the outlier battery cell as a battery cell with self-discharge abnormality.

2. The battery self-discharge screening method according to claim 1, characterized in that, The step of determining the outlier battery cell from the plurality of compensation currents comprises: generating a compensation current curve of each battery cell according to the compensation current of each battery cell at each sampling time within a preset time period; determining the outlier battery cell according to the compensation current curves.

3. The method of claim 2, wherein the battery self-discharge is determined by the following equation: ###0001### where, V is the battery self-discharge, I is the battery current, R is the battery resistance, and C is the battery capacitance. The step of determining the outlier battery cell according to the compensation current curves comprises: obtaining corresponding compensation currents of the compensation current curves at the same sampling time; calculating compensation current mean values of the plurality of compensation currents at the same sampling time; generating a total current mean value curve according to the plurality of compensation current mean values; calculating a difference value between each compensation current curve and the total current mean value curve; the difference value is represented by a root mean square error or an average absolute error of the difference between the compensation current and the compensation current mean value at all sampling times within the preset time period of the compensation current curve; determining a compensation current curve with a difference value greater than a preset value from the total current mean value curve as an outlier compensation current curve; regarding a battery cell corresponding to the outlier compensation current curve as an outlier battery cell.

4. The battery self-discharge screening method according to claim 1, characterized in that, The step of determining the outlier battery cell from the plurality of compensation currents comprises: for each battery cell, generating a corresponding compensation current mean value of each battery cell according to the compensation current at each sampling time within a preset time period; generating a total compensation current mean value according to the compensation current mean values corresponding to each battery cell; regarding a battery cell corresponding to a compensation current mean value with a deviation greater than a deviation threshold value from the total compensation current mean value as an outlier battery cell.

5. The method of claim 1, wherein the battery self-discharge screening method is characterized by, The step of obtaining the compensation currents required for maintaining the voltages of the plurality of battery cells at the preset voltages respectively comprises: performing current compensation on the battery cells with real-time voltages lower than the preset voltages; obtaining the compensation current of each battery cell at each sampling time within a preset time period.

6. The method of claim 5, wherein the battery self-discharge is determined by the following equation: ###0001### where V is the voltage of the battery, R is the internal resistance of the battery, I is the current of the battery, and t is the time. The step of obtaining the compensation current of each battery cell at each sampling time within a preset time period comprises: ​ obtaining the voltage of each battery cell at each sampling time within the preset time period; generating the compensation current of the battery cell according to the voltage of the battery cell, the preset voltage, and the resistance value of the battery cell.

7. The method of claim 6, wherein the battery self-discharge is determined by the following equation: ###0001### where V is the voltage of the battery, R is the internal resistance of the battery, I is the current of the battery, and t is the time. Before the step of obtaining the compensation currents required for maintaining the voltages of the plurality of battery cells at the preset voltages respectively, the method further comprises: ​ charging each battery cell to the preset voltage under the same condition; obtaining the real-time voltage of each battery cell.

8. The method of claim 7, wherein the battery self-discharge is determined by the following equation: ###0001### where V is the voltage of the battery, R is the internal resistance of the battery, I is the current of the battery, and t is the time. After each battery cell is charged to the preset voltage, the step of obtaining the real-time voltage of each battery cell is performed after a first preset time period. ​ 9. The battery self-discharge screening method according to claim 8, characterized in that, After each battery cell is charged to the preset voltage, and after a first preset time period, the method further comprises: The step of acquiring the voltage of each of the battery monomers at each sampling time within the preset time length is started at a second set time interval.

10. The method of claim 1, wherein the battery self-discharge screening method is characterized by, Further comprising: acquiring the temperature of each of the battery monomers at each sampling time; stopping the acquisition of the compensation current of the battery monomers when the temperature of the battery monomers is greater than an upper temperature limit value or less than a lower temperature limit value.

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