Battery cell screening method, device and equipment and storage medium

Abstract

The invention provides a battery cell screening method and device, equipment and a storage medium. The method comprises the following steps: S10, acquiring initial performance parameters of battery cells of the same batch; s20, obtaining the self-discharge impedance of the cells in the same batch; and S30, according to the initial performance parameters and the self-discharge impedance of the same batch of battery cells, performing consistency grouping on the same batch of battery cells to obtain shipment battery cells with consistent dynamic performance. According to the method, the influence on the service life and the safety of the battery caused by the difference between the single battery cells of the battery pack can be avoided, so that a user can have better experience in the use process.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and more specifically, to a method, device, equipment and storage medium for cell screening in the field of battery technology. Background Art

[0002] Lithium-ion batteries have become the main power source for digital products due to their high energy density, long life cycle, low self-discharge and low environmental pollution. Due to process fluctuations, even cells in the same batch will have differences. If they are randomly assembled without screening, these differences will seriously reduce the service life of the entire battery pack, so it is necessary to screen the batteries for consistency.

[0003] At present, capacity, internal resistance, and open circuit voltage are mostly used to screen the consistency of battery cells. However, the battery pack will still experience rapid capacity decay due to the mismatch between monomers. The time it takes for the monomer cells to reach the charge and discharge cut-off voltage is different. After the battery pack is disassembled into monomer cells, the internal resistance will show a greater difference. This shows that the initial screening using the three parameters of capacity, internal resistance, and open circuit voltage cannot reflect the characteristics of the monomer cells during later use. During use, the battery pack will be affected by the differences between the monomer cells, affecting the battery life and safety, which will result in a poor user experience. Therefore, how to prevent the battery pack from affecting the battery life and safety due to the differences between the monomer cells has become a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present application provides a method, device, equipment and storage medium for battery cell screening, which can prevent the battery pack from being affected by differences between single battery cells and affect the battery life and safety, so that users can have a better experience during use.

[0005] In a first aspect, a method for battery cell screening is provided, the method comprising: S10, obtaining initial performance parameters of battery cells of the same batch; S20, obtaining self-discharge impedance of the battery cells of the same batch; S30, grouping the battery cells of the same batch according to the initial performance parameters of the battery cells of the same batch and the self-discharge impedance, to obtain battery cells for shipment with consistent dynamic performance.

[0006] In the above technical scheme, the self-discharge impedance of the battery cell is introduced, and the battery cell consistency grouping is performed in combination with the self-discharge impedance and initial performance parameters of the battery cell. Since the self-discharge impedance of the battery cell can not only feedback the reversible capacity loss in later use, that is, power loss and polarization loss, but also feedback the irreversible capacity loss, that is, capacity loss and active material loss, the self-discharge impedance is to integrate various impedances into an overall impedance. Therefore, the self-discharge impedance can reflect the characteristics of the battery cell in the later use process, so that the self-discharge impedance can be further combined on the basis of the initial performance parameters to determine whether the battery cells of the same batch are consistent in the initial state and in the later use process. In addition, the parameter of self-discharge impedance is simple and easy to measure, and will not significantly increase the cost. Therefore, in this embodiment, a method for screening consistent batteries with simple and easy-to-measure parameters and without significantly increasing the cost is provided to avoid the battery pack affecting the life and safety of the battery due to differences between single batteries.

[0007] In combination with the first aspect, in some possible implementations, the step S20 includes: S201, obtaining the first open circuit voltage and the second open circuit voltage during the K value test of the battery cell; wherein the first open circuit voltage is measured after the first normal temperature resting, and the second open circuit voltage is measured after the second normal temperature resting; S202, after the first normal temperature resting and before the second normal temperature resting, performing a pulse test on the battery cell according to a preset charging rate and a preset pulse duration, and measuring the measured capacity of the battery cell after the pulse test; S204, calculating the capacitance of the battery cell according to the voltage difference between the first open circuit voltage and the second open circuit voltage and the measured capacity; S205, determining the relaxation time constant according to the first open circuit voltage, the first test time point at which the first open circuit voltage is measured, the second open circuit voltage, and the second test time point at which the second open circuit voltage is measured; S206, taking the ratio of the relaxation time constant to the capacitance as the self-discharge impedance of the battery cell.

[0008] In combination with the first aspect, in some possible implementations, the above-mentioned step S205 includes: S2051, calculating the logarithmic value of the above-mentioned first open circuit voltage, and determining a first target coordinate point with the above-mentioned first test time point as the horizontal coordinate and the logarithmic value of the above-mentioned first open circuit voltage as the vertical coordinate; S2052, calculating the logarithmic value of the above-mentioned second open circuit voltage, and determining a second target coordinate point with the above-mentioned second test time point as the horizontal coordinate and the logarithmic value of the above-mentioned second open circuit voltage as the vertical coordinate; S2053, performing curve fitting according to the above-mentioned first target coordinate point and the above-mentioned second target coordinate point to obtain a relaxation voltage-time curve; S2054, determining the negative inverse of the slope of the above-mentioned relaxation voltage-time curve as the above-mentioned relaxation time constant.

[0009] In combination with the first aspect, in some possible implementations, after the above S202, the above method also includes: S203, within a preset time length after the above pulse test, placing the above battery cell on a test channel and measuring the voltage of the above battery cell at N sampling time points to obtain N sampling voltages corresponding to the N sampling time points, the above preset time length is greater than or equal to 1 minute and less than or equal to 4 minutes, and the above N is greater than 3; the above S2053 includes: calculating the logarithmic values ​​of the sampling voltages corresponding to the above N sampling time points to obtain N third coordinate points with the sampling time points as the horizontal coordinates and the logarithmic values ​​of the sampling voltages as the vertical coordinates; performing curve fitting according to the above N third coordinate points, the above first target coordinate points and the above second target coordinate points to obtain a relaxation voltage-time curve.

[0010] In combination with the first aspect, in some possible implementations, the preset charging rate is greater than or equal to 0.5C and less than or equal to 1C, and / or the preset pulse duration is greater than or equal to 8 seconds and less than or equal to 12 seconds.

[0011] In combination with the first aspect, in some possible implementations, the second open circuit voltage is the highest voltage rebounded after the pulse test.

[0012] In combination with the first aspect, in some possible implementations, the above-mentioned S30 step includes: calculating the mean of the self-discharge impedances of the battery cells of the same batch; dividing the battery cells of the same batch into first-category battery cells and second-category battery cells according to the relationship between the self-discharge impedances of the battery cells of the same batch and the above-mentioned mean; wherein the self-discharge impedance of the above-mentioned first-category battery cells is greater than or equal to the above-mentioned mean, and the self-discharge impedance of the above-mentioned second-category battery cells is less than the above-mentioned mean; according to the initial performance parameters of the above-mentioned first-category battery cells, the above-mentioned first-category battery cells are consistently grouped to obtain first-category shipped battery cells with consistent dynamic performance; wherein the initial performance parameters of the above-mentioned first-category shipped battery cells are all within the first preset parameter range; according to the initial performance parameters of the above-mentioned second-category battery cells, the above-mentioned second-category battery cells are consistently grouped to obtain second-category shipped battery cells with consistent dynamic performance; wherein the initial performance parameters of the above-mentioned second-category shipped battery cells are all within the second preset parameter range.

[0013] In a second aspect, a device for screening battery cells is provided, the device comprising: a first acquisition module for acquiring initial performance parameters of battery cells of the same batch; a second acquisition module for acquiring self-discharge impedance of battery cells of the same batch; and a grouping module for grouping battery cells of the same batch according to the initial performance parameters of battery cells of the same batch and the self-discharge impedance to obtain battery cells for shipment with consistent dynamic performance.

[0014] In a third aspect, an electronic device is provided, comprising a memory and a processor. The memory is used to store executable program code, and the processor is used to call and run the executable program code from the memory, so that the electronic device executes the method in the first aspect or any possible implementation of the first aspect.

[0015] In a fourth aspect, a computer program product is provided, comprising: a computer program code, which, when executed on a computer, enables the computer to execute the method in the first aspect or any possible implementation of the first aspect.

[0016] In a fifth aspect, a computer-readable storage medium is provided, which stores a computer program code. When the computer program code runs on a computer, the computer executes the method in the above-mentioned first aspect or any possible implementation manner of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic flow chart of a method for cell screening provided in an embodiment of the present application;

[0018] Figure 2 is a schematic flowchart of an implementation method of S20 provided in an embodiment of the present application;

[0019] Figure 3 is a schematic diagram of an open circuit voltage of a battery cell before and after a pulse test provided in an embodiment of the present application;

[0020] Figure 4 is a schematic diagram of a relaxation voltage-time curve provided in an embodiment of the present application;

[0021] Figure 5 It is a schematic diagram of the difference in cycle performance provided by an embodiment of the present application;

[0022] Figure 6 It is a structural schematic diagram of a battery cell screening device provided in an embodiment of the present application;

[0023] Figure 7 It is a structural schematic diagram of an electronic device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0024] The technical solution in the present application will be described clearly and in detail below in conjunction with the accompanying drawings. In the description of the embodiments of the present application, unless otherwise specified, " / " means or, for example, A / B can mean A or B: "and / or" in the text is only a description of the association relationship of associated objects, indicating that there can be three relationships, for example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the embodiments of the present application, "multiple" means two or more than two.

[0025] In the following, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as suggesting or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features.

[0026] The development of lithium battery technology has always been centered on controlling costs, improving the energy density and power density of lithium batteries, enhancing safety, extending service life, and improving group consistency. The improvement of these factors is still the biggest challenge currently facing lithium batteries. The inconsistency of single cells is an important factor affecting the performance of battery packs. It can reduce the available capacity of the battery pack and reduce the cycle life of the battery pack. The cost of producing large batteries is often relatively high, so in order to meet the capacity or voltage requirements, small batteries are often required to be connected in series. The consistency of the battery will directly affect the performance of the battery pack, which is mainly manifested in three aspects:

[0027] First, capacity loss. Battery packs are composed of single cell types, and the capacity follows the barrel principle. The capacity of the worst cell determines the capacity of the entire battery pack.

[0028] The second aspect is the loss of life. The cell with the shortest life is the cell with the smallest capacity. Under the same charge and discharge time, each cycle is equivalent to overcharge and overdischarge, while for cells with larger capacity, each cycle is equivalent to shallow charge and shallow discharge. In this way, the difference between low-capacity and high-capacity cells will become larger and larger, and it is very likely that the small-capacity single cell will reach the end of its life first. When the life of a cell ends, a group of cells welded together will also end their life.

[0029] Third, the internal resistance increases. For cells with different internal resistances and the same current, cells with large internal resistance will generate more heat. If the battery temperature is too high, the degradation rate will accelerate, and the internal resistance will further increase. The internal resistance and temperature rise form a pair of negative feedback, which accelerates the degradation of cells with high internal resistance.

[0030] At present, the parameters that characterize the consistency of battery cells are mainly capacity, internal resistance, and open circuit voltage. There are two main reasons for battery inconsistency, namely, the differences generated during use and the differences in the initial state of the battery cells. The initial parameter inconsistency of the former accumulates with the continuous charge and discharge cycles of the battery during use, resulting in greater differences in the conditions of each single cell (SOC, voltage, etc.). The operating environment in the lithium battery pack is also different for each single cell, which will also lead to increased inconsistency of the single cell, and ultimately lead to premature failure of lithium-ion batteries. The latter is that the battery cell itself is initially a problem of the manufacturing process during the customization of lithium-ion batteries and the unevenness of the battery material, which makes the capacity and internal resistance of the same batch of the same model of batteries different.

[0031] Specifically, the reasons for the inconsistency of lithium battery packs may be as follows:

[0032] First, the parameter differences between single cells: The state differences between single cells mainly include the initial differences of single cells and the parameter differences generated during use. There are many uncontrollable factors in the design, manufacturing, storage and use of batteries, which will affect the consistency of batteries. Improving the consistency of single cells is a prerequisite for improving the performance of battery packs. The mutual influence of single cell parameters, the current parameter state is affected by the initial state and the cumulative effect of time.

[0033] Second, charging and discharging conditions: the charging method affects the charging efficiency and charging state of the lithium battery pack. Overcharging and over-discharging will damage the battery. After multiple charging and discharging, the battery pack will show inconsistency. At present, there are several ways to charge lithium-ion batteries, but the most common ones are segmented constant current charging and constant current constant voltage charging. Constant current charging is an ideal method that can be fully charged safely and effectively; constant current constant voltage charging effectively combines the advantages of constant current charging and constant voltage charging, solves the problem that the general constant current charging method is difficult to fully charge accurately, and avoids the impact of excessive current on the battery in the initial charging stage of the constant voltage charging method. The operation is simple and convenient.

[0034] Third, temperature: Differences in battery pack design and use environment will cause inconsistent temperature environments for single cells. According to the Arrhenius law, the electrochemical reaction rate constant of the battery is exponentially related to the temperature, and the electrochemical characteristics of the battery are different at different temperatures. Temperature will affect the operation of the battery electrochemical system, coulomb efficiency, charge and discharge capabilities, output power, capacity, reliability and cycle life. At present, the main research is on the quantitative study of the impact of temperature on battery pack inconsistency.

[0035] Fourth, battery external circuit: In a large-scale energy storage system, the batteries will be combined in series and parallel, so there will be many connecting circuits and control elements between the batteries and modules. Due to the different performance and aging speed of each structural part or component, and the inconsistent energy consumed at each connection point, different devices have different effects on the battery, resulting in inconsistency in the battery pack system. The inconsistency of the battery decay rate in the parallel circuit will accelerate the deterioration of the system. In addition, the battery management system (Battery Management System, BMS) is the guarantee for the normal operation of the battery pack, but the BMS input circuit will have an adverse effect on the consistency of the battery. The battery voltage monitoring methods include precision resistor voltage division, integrated chip sampling, etc. These methods cannot avoid external leakage current of the sampling line due to the existence of resistors and circuit board paths. The voltage sampling input impedance of the battery management system will increase the inconsistency of the battery state of charge (State of Charge, SOC) and affect the performance of the battery pack.

[0036] Fifth, SOC estimation error: The reasons for SOC inconsistency include inconsistent initial nominal capacity of single cells and inconsistent nominal capacity decay speed of single cells during operation. For parallel circuits, the difference in internal resistance of single cells will cause uneven current distribution, which in turn leads to inconsistent SOC.

[0037] Under the existing production and process levels, there are three common ways to solve the consistency problem of lithium-ion batteries:

[0038] First, reasonable sorting: put cells with similar performance parameters in a battery pack and try to make the initial state of the cells consistent. The purpose of reasonable sorting is to select cells with similar performance parameters. Sorting methods have been studied for many years and are mainly divided into two categories: static sorting and dynamic sorting.

[0039] Second, improve the thermal management level: provide lithium-ion batteries with a more suitable and uniform working environment temperature to prevent the initial inconsistency from further deteriorating. The addition of a thermal management system can adjust the temperature difference of the entire battery pack to keep it within a smaller range. The battery cells that generate more heat will still have a higher temperature rise, but will not be more different from other battery cells, and there will not be a significant difference in the degradation level.

[0040] Third, battery balance: BMS is designed with a balance function to ensure a good use environment for lithium-ion battery packs, keep the temperature constant as much as possible, reduce vibration, and prevent water, dust, etc. from contaminating the battery poles. Understand the development law of the inconsistency of single cells in lithium-ion battery packs, adjust or replace the battery with pole parameters in time, and ensure that the inconsistency of battery pack parameters does not increase with the use time.

[0041] In addition to the above methods for improving battery consistency, adding battery screening parameters in the initial stage of battery testing can also increase battery consistency.

[0042] For example, using charging capacity, discharging capacity, internal resistance, constant current charging ratio and rate as initial screening parameters, the batteries of the same batch are discharged and then charged, and the batteries whose difference between charging capacity and rated capacity meets the requirements are screened out; the screened batteries are discharged and then charged, and the batteries whose difference between discharge capacity and rated capacity and discharge capacity meet the requirements are screened out; the screened batteries are charged, and the batteries with internal resistance difference ≤0.2mΩ are screened out, and the ratio of constant current charging to charging capacity ≥98% are screened out. The screened batteries are charged and then discharged, and the batteries with voltage drop ≥2.85V and discharge capacity to rated capacity ratio ≥90% are screened out. The batteries screened out in the above method can maintain good battery consistency in terms of charging capacity and rate discharge, but the method process is complicated, and additional testing is required, which increases manufacturing costs.

[0043] Another example is to obtain the charge capacity and battery voltage of a single cell in real time when it is charged for the first time; draw a first dQ / dV-capacity curve based on the charge capacity and battery voltage of the first charge; take the horizontal coordinate value of the preset point in all the valley areas in the first dQ / dV-capacity curve as the reference capacity; charge the battery system externally and obtain the charge capacity and battery voltage of each single cell in real time; draw a second dQ / dV-capacity graph based on the charge capacity and battery voltage of each single cell during the external charging process; extract the horizontal coordinate value of each corresponding point in each second dQ / dV-capacity graph as the measured capacity; analyze the consistency of the battery system based on the measured capacity and the reference capacity. This method requires a small rate discharge, which also requires additional large costs.

[0044] Based on this, the embodiment of the present application aims to provide a method for screening cells with consistency, which is simple and easy to measure and does not significantly increase the cost, so as to avoid the battery pack being affected by the differences between the single cells and the life and safety of the battery. The method for screening cells is applied to electronic equipment, which can be specifically a test device.

[0045] Figure 1 It is a schematic flow chart of a method for cell screening provided in an embodiment of the present application.

[0046] For example, Figure 1 As shown, the method includes:

[0047] S10, obtaining initial performance parameters of the battery cells of the same batch.

[0048] S20, obtaining the self-discharge impedance of the battery cells of the same batch.

[0049] S30, grouping the battery cells of the same batch according to their initial performance parameters and self-discharge impedance to obtain battery cells with consistent dynamic performance for shipment.

[0050] exist Figure 1 In the illustrated embodiment, the self-discharge impedance of the battery cell is introduced, and the battery cell consistency grouping is performed in combination with the self-discharge impedance and initial performance parameters of the battery cell. Since the self-discharge impedance of the battery cell can not only feedback the reversible capacity loss in later use, that is, power loss and polarization loss, but also feedback the irreversible capacity loss, that is, capacity loss and active material loss, the self-discharge impedance is to integrate various impedances into an overall impedance. Therefore, the self-discharge impedance can reflect the characteristics of the battery cell in the later use process, so that the self-discharge impedance can be further combined on the basis of the initial performance parameters to determine whether the battery cells of the same batch are consistent in the initial state and in the later use process. In addition, the parameter of self-discharge impedance is simple and easy to measure, and will not significantly increase the cost. Therefore, in this embodiment, a method for screening consistent batteries with simple and easy-to-measure parameters and without significantly increasing the cost is provided to avoid the battery pack affecting the life and safety of the battery due to differences between single batteries.

[0051] Below Figure 1 The implementation method of each step in the embodiment shown is specifically described:

[0052] In S10, the initial performance parameters of the battery cell can be understood as the performance parameters of the battery cell in the initial state, such as the usage capacity, internal resistance, and open circuit voltage of the battery cell in the initial state. Among them, the initial state can be understood as the state of the finished battery cell obtained after formation and capacity testing. The open circuit voltage refers to the terminal voltage of the battery cell in the open circuit state.

[0053] In S20, the self-discharge impedance can be understood as: the impedance that hinders the leakage current of the battery cell in the absence of an external power supply. Among them, the leakage current can also be understood as the self-discharge current of the battery cell. The self-discharge current of the battery cell is usually small and belongs to the micro-ampere or nano-ampere level. The self-discharge impedance is different from the discharge impedance. The discharge impedance is the impedance that hinders the discharge current of the battery cell in the presence of an external power supply.

[0054] In an exemplary embodiment, the implementation of S20 can refer to Figure 2 , including S201 to S206. Specifically:

[0055] S201, obtaining a first open circuit voltage and a second open circuit voltage during a K value test of the battery cell; wherein the first open circuit voltage is measured after a first normal temperature rest, and the second open circuit voltage is measured after a second normal temperature rest.

[0056] Among them, the K value test refers to an indicator used to measure the self-discharge rate of lithium batteries in the lithium battery industry. In this embodiment, the K value can be understood as a physical quantity used to describe the self-discharge rate of the battery cell, and its calculation method is the difference between the open circuit voltages of the two tests divided by the time interval △t between the two voltage tests, and the formula is: K = (OCV2-OCV1) / △t. The above-mentioned first open circuit voltage and the second open circuit voltage can be OCV1 and OCV2 in the above-mentioned K value test, respectively. The above-mentioned first room temperature standing and the second room temperature standing are both standing steps in the existing K value test process, and the above-mentioned first open circuit voltage and the second open circuit voltage are also two physical quantities that will be tested in the existing K value test process. In other words, in the embodiment of the present application, there is no need to add additional test steps to test and obtain OCV1 and OCV2, but OCV1 and OCV2 that will be tested in the K value test process can be directly obtained based on the existing K value test process.

[0057] Exemplarily, the test flow of OCV1 and OCV2 in the K value test process may include: the bare cell is subjected to formation and capacity testing after being sealed at the top and side, sprayed with code, vacuum dried, injected with electrolyte, and left standing at high temperature. After obtaining the finished cell, it is first left standing at high temperature for a first preset time, and then left standing at room temperature for a second preset time. After leaving standing at room temperature for the second preset time, the OCV1 of the cell is tested. After OCV1 is obtained through the test, it is left standing at room temperature for a third preset time, and after leaving standing at room temperature for the third preset time, the OCV2 of the cell is tested. The above-mentioned first preset time, second preset time and third preset time can all be set according to actual needs, and the first preset time, second preset time and third preset time can be the same or different. The above-mentioned three preset time can be optionally set to 2 days, but this embodiment does not specifically limit this.

[0058] Specifically, the first normal temperature resting involved in this embodiment may be the second preset time length of the normal temperature resting, and the second normal temperature resting involved in this embodiment may be the third preset time length of the normal temperature resting.

[0059] In an exemplary embodiment, the second open circuit voltage is the highest voltage rebounded after the pulse test. Figure 3 , Figure 3 A schematic diagram showing the open circuit voltage of the battery cell before and after the pulse test. Figure 3 It can be seen that the second open circuit voltage is the highest voltage rebounded after the pulse test, that is, Figure 3 The voltage U2 remains unchanged after the pulse test, and the first open circuit voltage is Figure 3 Wherein is the stable voltage U1 before the pulse test, so the voltage difference ΔU between the first open circuit voltage and the second open circuit voltage = U1-U2.

[0060] S202, after the first normal temperature rest and before the second normal temperature rest, pulse test the battery cell according to a preset charging rate and a preset pulse duration, and measure the measured capacity of the battery cell after the pulse test.

[0061] Among them, the pulse test can also be understood as a charging test on the battery cell after OCV1 is tested and before OCV2 is tested. For example, in the above-mentioned K value test process, after OCV1 is tested, the battery cell can be pulse tested according to the preset charging rate and the preset pulse duration, and the measured capacity of the battery cell can be measured after the pulse test. Then, the battery cell is left to stand at room temperature for a third preset time, and the OCV2 of the battery cell is tested after the battery cell is left to stand at room temperature for a third preset time. In other words, the OCV2 is measured after the battery cell has been pulse tested.

[0062] In a specific implementation, the above-mentioned preset pulse duration can be shorter. Although the pulse test and the capacity measurement step after the pulse test are equivalent to the newly added test steps in the K value test process in the prior art, since the test duration of the test step is shorter and the test method is simpler, it can be considered that the added step will not increase the overall manufacturing and testing costs.

[0063] In an exemplary embodiment, the preset charging rate is greater than or equal to 0.5C and less than or equal to 1C, and / or the preset pulse duration is greater than or equal to 8 seconds and less than or equal to 12 seconds. Considering that the test equipment has a certain test accuracy, if the preset charging rate is too small, it may be difficult to provide a too small preset charging rate to the battery cell due to insufficient accuracy of the test equipment, which may easily cause the charging current of the battery cell to be inaccurate and inconsistent with expectations. If the preset charging rate is too large, it will lead to large polarization, which will lead to a long time for restoration of stability, and ultimately lead to a long waiting time to test and obtain a stable and accurate ΔU, that is, ΔU is not easy to measure. Therefore, in this embodiment, setting the preset charging rate at 0.5C to 1C is just right, which is conducive to saving test resources and obtaining accurate and stable results. It can be understood that if the preset pulse duration is too short, ΔU may not change significantly, that is, ΔU is very small and may exceed the accuracy range that the test equipment can measure. If the preset pulse duration is too long, ΔU is basically unchanged and there is no need to test it again. Therefore, in this embodiment, the preset pulse duration is set between 8s and 12s, which is beneficial to saving test resources and obtaining accurate and stable results.

[0064] Optionally, the preset charging rate may be 1C, and the preset pulse duration may be 10S.

[0065] S204, calculating the capacitance of the battery cell according to the voltage difference between the first open circuit voltage and the second open circuit voltage and the measured capacity.

[0066] Specifically, if the voltage difference between the first open circuit voltage and the second open circuit voltage is recorded as ΔU, the above-mentioned measured capacity is recorded as Qpulse, and the calculated capacitance of the battery cell is recorded as Cpulse, the capacitance of the battery cell can be calculated by the following formula: Cpulse=Qpulse / ΔU.

[0067] S205 , determining a relaxation time constant according to the first open circuit voltage, a first test time point at which the first open circuit voltage is measured, the second open circuit voltage, and a second test time point at which the second open circuit voltage is measured.

[0068] The relaxation time constant is specifically a constant, which can be understood in a physical sense as: the time required for the battery cell to recover to its original state, i.e., the state before the external stimulus, after a brief change caused by an external stimulus. The external stimulus can be understood as the above-mentioned pulse test.

[0069] In an exemplary embodiment, the implementation of the above S205 may include the following S2051 to S2054, including:

[0070] S2051, calculating the logarithmic value of the first open circuit voltage, and determining a first target coordinate point with the first test time point as the abscissa and the logarithmic value of the first open circuit voltage as the ordinate.

[0071] Specifically, the logarithmic value of the first open circuit voltage can be expressed as Ln(OCV1), and if the first test time point is recorded as t1, the first target coordinate point can be expressed as (t1, Ln(OCV1)), where t1 is the abscissa of the first target coordinate point, and Ln(OCV1) is the ordinate of the first target coordinate point.

[0072] S2052, calculating the logarithmic value of the second open circuit voltage, and determining a second target coordinate point with the second test time point as the abscissa and the logarithmic value of the second open circuit voltage as the ordinate.

[0073] Specifically, the logarithmic value of the second open circuit voltage can be expressed as Ln(OCV2), and if the second test time point is recorded as t2, the second target coordinate point can be expressed as (t2, Ln(OCV2)), where t2 is the abscissa of the second target coordinate point, and Ln(OCV2) is the ordinate of the second target coordinate point.

[0074] S2053, performing curve fitting according to the first target coordinate point and the second target coordinate point to obtain a relaxation voltage-time curve.

[0075] The horizontal coordinate of the relaxation voltage-time curve is time, and the vertical coordinate is the logarithmic value of voltage. In this embodiment, the first target coordinate point and the second target coordinate point can be used as points on the relaxation voltage-time curve to fit the relaxation voltage-time curve.

[0076] It is understandable that, since the voltage OCV and time are usually in an exponential function relationship, the logarithmic value of OCV and time will be in a linear relationship. Therefore, the relaxation voltage-time curve in this embodiment can be a straight line that satisfies a certain linear relationship under ideal conditions.

[0077] S2054, determining the negative inverse of the slope of the relaxation voltage-time curve as the relaxation time constant.

[0078] It can be understood that, according to the above description, the relaxation voltage-time curve is actually a straight line that satisfies a certain linear relationship. Therefore, in this embodiment, the negative inverse of the slope of the straight line can be determined as the relaxation time constant.

[0079] S206, using the ratio of the relaxation time constant to the capacitance as the self-discharge impedance of the battery cell.

[0080] Specifically, if the relaxation time constant is recorded as τself, the capacitance calculated in the above S204 is recorded as Cpulse, and the self-discharge impedance is recorded as Rself, then the self-discharge impedance can be calculated by the following formula: Rself=τself / Cpulse.

[0081] In an exemplary embodiment, after the above S202, the method further includes:

[0082] S203, within a preset time after the pulse test, the battery cell is placed on the test channel and the voltage of the battery cell is measured at N sampling time points to obtain N sampling voltages corresponding to the N sampling time points, the preset time is greater than or equal to 1 minute and less than or equal to 4 minutes, and N is greater than 3.

[0083] Among them, leaving the battery cell stationary on the test channel can be understood as placing the battery cell on the test equipment without removing it, so that within the preset time after the pulse test, the voltage of the battery cell is measured at N different sampling time points to obtain the sampling voltages corresponding to the N sampling time points, so that N sampling voltages can be obtained. Since the above-mentioned N sampling voltages are tested by leaving the battery cell stationary on the test channel, the N sampling voltages can be understood as online voltages obtained by online testing, and the above-mentioned first open-circuit voltage and second open-circuit voltage can be understood as offline voltages obtained by removing the battery cell from the test channel for offline testing.

[0084] In this embodiment, the preset time is set to 1 minute to 4 minutes mainly because if the preset time is too short, the number of effective voltages obtained by sampling may be insufficient, and if the preset time is too long, the size of the effective voltage obtained by sampling will remain fixed and there is no need to sample again. Figure 3 It can be seen that the voltage of the battery cell will remain fixed for a period of time after the pulse test. Therefore, in this embodiment, setting the preset duration to 1 minute to 4 minutes is conducive to avoiding unnecessary sampling while sampling to obtain a sufficient number of effective voltages, thereby saving test resources. Optionally, the voltage of the battery cell can be sampled at least at 4 different sampling time points within the above preset duration to obtain at least the sampled voltages corresponding to 4 different sampling times.

[0085] For example, through the above Figure 3 It can be seen that after 2 minutes after the pulse test, that is, at 51 minutes, the voltage of the battery cell remains basically unchanged, so the above preset time length can be set to 2 minutes. That is, in this embodiment, within 2 minutes after the pulse test, the battery cell can be left stationary on the test channel and the voltage of the battery cell can be measured at N sampling time points to obtain the sampling voltages corresponding to the N sampling time points. Optionally, a sampling voltage can be sampled every 30 seconds within 2 minutes after the pulse test to obtain the sampling voltages corresponding to the 4 sampling time points. Theoretically, in order to obtain more sampling voltages, a larger number of sampling voltages can also be sampled within the above 2 minutes.

[0086] Exemplarily, the number of sampled voltages sampled within the above-mentioned preset time length can be set according to actual needs. Since the sampled voltages sampled at different sampling time points are mainly used to increase the coordinate points of the fitting relaxation voltage-time curve. The more sampled voltages are sampled, the more coordinate points are subsequently used to fit the relaxation voltage-time curve, and the more accurate the relaxation voltage-time curve is finally fitted.

[0087] Optionally, the N sampling time points may be N sampling time points evenly distributed within the preset time length, which is beneficial for making the coordinate points used to fit the relaxation voltage-time curve as evenly distributed as possible, thereby facilitating improving the accuracy of the fitted relaxation voltage-time curve.

[0088] In this embodiment, in order to ensure the accuracy of curve fitting while saving testing resources, 10 sampling voltages can be obtained by sampling within a preset time length. For example, the voltage of the battery cell is tested at 10 different sampling time points to obtain 10 sampling voltages. The 10 sampling time points can be 10 sampling points evenly distributed within the above-mentioned preset time length.

[0089] In the case where S203 is also included after the above S202, the above S2053 may further include: calculating the logarithmic values ​​of the sampling voltages corresponding to N sampling time points to obtain N third coordinate points with the sampling time points as the horizontal coordinates and the logarithmic values ​​of the sampling voltages as the vertical coordinates; performing curve fitting based on the N third coordinate points, the first target coordinate points and the second target coordinate points to obtain a relaxation voltage-time curve.

[0090] Specifically, the sampling time point can be recorded as Ti, and the logarithmic value of the voltage corresponding to N different pairs of sampling time points can be recorded as Ln(Vi). Wherein, i=1, 2, 3....N, N is the total number of sampled voltages sampled within the above-mentioned preset time length. Based on this, N third coordinate points can be obtained, and the N third coordinate points can be expressed as: (Ti, Ln(Vi)). Therefore, according to the N third coordinate points (Ti, Ln(Vi)), the above-mentioned first target coordinate point (t1, Ln(OCV1)) and the second target coordinate point (t2, Ln(OCV2)), curve fitting can be performed to obtain a relaxation voltage-time curve.

[0091] For example, the schematic diagram of the relaxation voltage-time curve obtained by fitting can be found in Figure 4 , the expression of the relaxation voltage-time curve can be y=-7E-05x+1.4971. Where, Figure 4 R 2 =0.9925 indicates that the logarithmic value of voltage and time have a good correlation.

[0092] In S30, the battery cells of the same batch are grouped according to their initial performance parameters and self-discharge impedance to obtain battery cells for shipment with consistent dynamic performance.

[0093] For example, the battery cells of the same batch can be first grouped for static consistency according to their initial performance parameters to obtain preliminary selected battery cells with consistent static performance. Then, dynamic consistency grouping can be further performed based on the self-discharge impedance of the preliminary selected battery cells with consistent static performance to obtain shipping battery cells with consistent dynamic performance. Among them, preliminary selected battery cells with consistent static performance can be understood as battery cells with consistent initial performance parameters. Shipping battery cells with consistent dynamic performance can be understood as battery cells with basically consistent self-discharge impedance among battery cells with consistent initial performance parameters. Among them, battery cells with basically consistent self-discharge impedance can be understood as battery cells with self-discharge impedance greater than or equal to the average of the self-discharge impedance of battery cells of the same batch, or battery cells with self-discharge impedance less than the average of the self-discharge impedance of battery cells of the same batch.

[0094] In an exemplary embodiment, the implementation of the above step S30 may include the following steps S301 to S304:

[0095] S301, calculating the average self-discharge impedance of the battery cells in the same batch.

[0096] Specifically, the self-discharge impedance of each battery cell in the same batch can be determined by the above-mentioned method of determining the self-discharge impedance in the above-mentioned embodiment, such as the above-mentioned S201 to S206. Then, the average value of the self-discharge impedance of the battery cells in the same batch is calculated according to the self-discharge impedance of each battery cell in the same batch.

[0097] S302, dividing the battery cells of the same batch into first-category battery cells and second-category battery cells according to the relationship between the self-discharge impedance of the battery cells of the same batch and the above-mentioned mean value; wherein the self-discharge impedance of the first-category battery cells is greater than or equal to the mean value, and the self-discharge impedance of the second-category battery cells is less than the mean value.

[0098] Specifically, since the self-discharge impedance of the first type of battery cell is greater than or equal to the average value, the first type of battery cell can also be called a high-resistance battery cell. Correspondingly, since the self-discharge impedance of the second type of battery cell is less than the average value, the second type of battery cell can also be called a low-resistance battery cell.

[0099] S303, grouping the first category of battery cells according to their initial performance parameters to obtain first category of shipped battery cells with consistent dynamic performance; wherein the initial performance parameters of the first category of shipped battery cells are all within a first preset parameter range.

[0100] Among them, multiple initial performance parameters can respectively correspond to their own first preset parameter ranges, and multiple initial performance parameters of the first category of battery cells can be obtained. Among the first category of battery cells, the battery cells whose multiple initial performance parameters are all within their respective corresponding first preset parameter ranges are regarded as the first category of shipped battery cells with consistent dynamic performance.

[0101] Exemplarily, the first type of battery cells can be grouped for consistency based on at least three initial performance parameters and the corresponding first preset parameter ranges to obtain the first type of shipped battery cells with consistent dynamic performance. The initial performance parameters may include battery cell capacity, battery cell internal resistance, and battery cell open circuit voltage. The corresponding first preset parameter range includes battery cell capacity range, battery cell internal resistance range, and battery cell open circuit voltage range.

[0102] S304, grouping the second type of battery cells according to their initial performance parameters to obtain second type of shipping battery cells with consistent dynamic performance; wherein the initial performance parameters of the second type of shipping battery cells are all within a second preset parameter range.

[0103] Among them, multiple initial performance parameters can respectively correspond to their own second preset parameter ranges, and multiple initial performance parameters of the second type of battery cells can be obtained. Among the second type of battery cells, the battery cells whose multiple initial performance parameters are all within their respective corresponding second preset parameter ranges are regarded as second type shipping battery cells with consistent dynamic performance.

[0104] Exemplarily, the second type of battery cells can be grouped for consistency based on at least three initial performance parameters and the corresponding second preset parameter ranges to obtain the second type of shipped battery cells with consistent dynamic performance. Among them, the initial performance parameters may include battery cell capacity, battery cell internal resistance, and battery cell open circuit voltage. The corresponding second preset parameter range includes battery cell capacity range, battery cell internal resistance range, and battery cell open circuit voltage range.

[0105] It should be noted that, in a specific implementation, the first preset parameter range and the second preset parameter range can be set according to actual needs and the two can be the same or different, and this embodiment does not make any specific limitation on this.

[0106] For ease of understanding, the method for cell screening in the embodiment of the present application is described below with a specific example, and the process of the method may include the following S40 to S46:

[0107] S40, using aluminum foil as the cathode current collector, uniformly coating a layer of lithium cobalt oxide slurry on the surface of the aluminum foil, the composition of the lithium cobalt oxide slurry is 97.8wt% LiCoO2 (LCO), 0.8wt% polyvinylidene fluoride (PVDF) and 1.4wt% conductive carbon black, and then cold pressing to prepare a positive electrode sheet. Using copper foil as the anode current collector, uniformly coating a layer of graphite slurry on the surface of the copper foil, the slurry composition is a combination of 97.7wt% artificial graphite, 1.3wt% carboxymethyl cellulose (CMC) and 1.0wt% styrene butadiene rubber (SBR), and then cold pressing to prepare a negative electrode sheet.

[0108] S41, the positive electrode sheet and the negative electrode sheet are wound after being stripped, and the positive electrode sheet and the negative electrode sheet are separated by a PE isolation film, so as to prepare a wound bare cell. The bare cell is sealed at the top and side, sprayed with code, vacuum dried, injected with electrolyte, and placed at high temperature for formation and capacity testing to obtain a finished cell. The finished cell is placed at high temperature for 2 days, and then placed at room temperature for 2 days to test the first open circuit voltage OCV1 of the cell.

[0109] S42, after OCV1 is obtained by the test, a pulse test is performed on the battery cell at a charging rate of 1C for 10 seconds, and the capacity Qpulse of the battery cell is recorded. After the pulse test, the battery cell is left to stand on the test channel for 2 minutes, and then left to stand at room temperature for 2 days, and the open circuit voltage OCV2 of the battery cell is tested again. The battery cell is left to stand on the test channel for 2 minutes, and N sampling voltages are obtained at N different sampling time points within the 2 minutes, where N is greater than 3.

[0110] S43, calculating the capacitance Cpulse of the battery cell according to the above OCV2, OCV1 and Qpulse.

[0111] Assuming that Qpulse is 6.84 mA.h and ΔU is OCV1-OCV2=0.0057 V, then Cpulse=Qpulse / ΔU=6.84 / 5.7=1.2.

[0112] S44, calculate the relaxation time constant τself.

[0113] Specifically, the relaxation voltage-time curve can be obtained by fitting the N sampling voltages obtained by sampling at the N sampling time points within the above 2 minutes, the OCV1 obtained by the first test time point, and the OCV2 obtained by the second test time point. The logarithmic value of OCV and time show a good linear relationship. For example, the schematic diagram of the relaxation voltage-time curve can be referred to Figure 4 . Figure 4 The negative inverse of the slope of the relaxation voltage-time curve is τself=21392.

[0114] S45, calculating the self-discharge impedance of the battery cell according to the relaxation time constant τself and the capacitance Cpulse of the battery cell.

[0115] Assuming that τself=21392, Cpulse=1.2, the self-discharge impedance Rself=τself / Cpulse=21392 / 1.2=17827Ω.

[0116] S46, using the average value of the self-discharge impedance of the cells in the same batch as the boundary, divide them into high-resistance cells and low-resistance cells, and under the premise of capacity, internal resistance, and open-circuit voltage screening rules, high-resistance cells are matched with high-resistance cells to obtain the above-mentioned first type of shipping cells, and low-resistance cells are matched with low-resistance cells to obtain the above-mentioned second type of shipping cells.

[0117] For example, the consistency of the shipped cells obtained by the cell screening method in this embodiment is better, and after being assembled into a cell module Pack, the life of the Pack can be greatly improved. Figure 5 , Figure 5Curve 1 and curve 2 in the figure are both cycle life test curves, curve 1 is the cycle life test curve of module A, and curve 2 is the cycle life test curve of module B. Figure 5 The horizontal axis of the curve in is the number of cycle tests Cycle_No, and the vertical axis is the capacity retention rate Capacity_retention. Module A is a cell module obtained by combining the self-discharge impedance Rself (With Rself) of the cell and the initial state parameters to perform cell consistency grouping. Module B is a cell module obtained by performing cell consistency grouping based on the initial state parameters but without combining the self-discharge impedance Rself (Without Rself). Figure 5 It can be seen that the capacity retention rate of module A is 82%, which is higher than the capacity retention rate of module B, which is 60%. The capacity retention rate of module A has been significantly improved. It can be seen that combining the self-discharge impedance and initial state parameters of the battery cell for battery cell consistency grouping results in better dynamic consistency and better cycle performance of the battery cell module.

[0118] In this embodiment, a new parameter, namely the self-discharge impedance Rself, is added for the consistency screening of battery cells. This parameter is simple and easy to measure, and will not significantly increase the cost. The self-discharge impedance Rself can provide feedback on the reversible capacity loss and irreversible capacity loss in later use, and integrates various impedances into an overall impedance. In addition, a method for measuring the self-discharge impedance is designed, and this measurement method will not significantly increase the testing cost. Specifically, the self-discharge impedance Rself is the ratio of the relaxation time constant τself to the pulse capacitance Cpulse, τself is the negative inverse of the slope of the relaxation voltage-time curve, and Cpulse is the ratio of the pulse capacity Cpulse to the relaxation voltage difference (that is, the difference between the first open circuit voltage and the second open circuit voltage) ΔU. As Figure 3 As shown, ΔU is the voltage difference between the stable voltage before the pulse and the highest voltage rebounded after the pulse. In order not to increase the manufacturing and testing costs, the relaxation time constant τself is calculated using the open circuit voltage of the two room temperature static conditions in the K value test and the N sampled voltages collected at N time points within 2 minutes after the pulse test to form a relaxation voltage-time curve. This is equivalent to adding a 1C, 10s pulse test before the second room temperature static condition in the existing K value test process and a sampling step of N sampled voltages within 2 minutes after the 10s pulse. Since the pulse test and the sampling voltage account for a very small proportion of the entire process, the cost will not be significantly increased due to the addition of the test link for the self-discharge impedance Rself.

[0119] Figure 6 It is a structural schematic diagram of a battery cell screening device provided in an embodiment of the present application.

[0120] For example, Figure 6As shown, the device includes: a first acquisition module 601, used to obtain the initial performance parameters of the battery cells of the same batch; a second acquisition module 602, used to obtain the self-discharge impedance of the battery cells of the same batch; a grouping module 603, used to group the battery cells of the same batch according to the initial performance parameters of the battery cells of the same batch and the self-discharge impedance, so as to obtain the shipped battery cells with consistent dynamic performance.

[0121] In one possible implementation, the second acquisition module 602 includes: an open circuit voltage acquisition module, which is used to obtain the first open circuit voltage and the second open circuit voltage during the K value test of the above-mentioned battery cell; wherein the above-mentioned first open circuit voltage is measured after the first normal temperature resting, and the above-mentioned second open circuit voltage is measured after the second normal temperature resting; a measurement capacity determination module, which is used to perform a pulse test on the above-mentioned battery cell according to a preset charging rate and a preset pulse duration after the above-mentioned first normal temperature resting and before the above-mentioned second normal temperature resting, and measure the measured capacity of the above-mentioned battery cell after the pulse test; a capacitance calculation module, which is used to calculate the capacitance of the above-mentioned battery cell according to the voltage difference between the above-mentioned first open circuit voltage and the above-mentioned second open circuit voltage and the above-mentioned measured capacity; a relaxation time constant determination module, which is used to determine the relaxation time constant according to the above-mentioned first open circuit voltage, the first test time point at which the above-mentioned first open circuit voltage is measured, the above-mentioned second open circuit voltage, and the second test time point at which the above-mentioned second open circuit voltage is measured; a self-discharge impedance determination module, which is used to use the ratio of the above-mentioned relaxation time constant to the above-mentioned capacitance as the self-discharge impedance of the above-mentioned battery cell.

[0122] In one possible implementation, the relaxation time constant determination module is specifically used to: calculate the logarithmic value of the above-mentioned first open circuit voltage, and determine a first target coordinate point with the above-mentioned first test time point as the horizontal coordinate and the logarithmic value of the above-mentioned first open circuit voltage as the vertical coordinate; calculate the logarithmic value of the above-mentioned second open circuit voltage, and determine a second target coordinate point with the above-mentioned second test time point as the horizontal coordinate and the logarithmic value of the above-mentioned second open circuit voltage as the vertical coordinate; perform curve fitting according to the above-mentioned first target coordinate point and the above-mentioned second target coordinate point to obtain a relaxation voltage-time curve; and determine the negative inverse of the slope of the above-mentioned relaxation voltage-time curve as the above-mentioned relaxation time constant.

[0123] In a possible implementation, the device further includes: a voltage sampling module, which is used to place the battery cell on a test channel within a preset time after the pulse test and measure the voltage of the battery cell at N sampling time points to obtain N sampling voltages corresponding to the N sampling time points, wherein the preset time is greater than or equal to 1 minute and less than or equal to 4 minutes, and N is greater than 3; a relaxation time constant determination module, which is specifically used to: calculate the logarithmic values ​​of the sampling voltages corresponding to the N sampling time points to obtain N third coordinate points with the sampling time points as the horizontal coordinates and the logarithmic values ​​of the sampling voltages as the vertical coordinates; perform curve fitting based on the N third coordinate points, the first target coordinate points and the second target coordinate points to obtain a relaxation voltage-time curve.

[0124] In a possible implementation, the preset charging rate is greater than or equal to 0.5C and less than or equal to 1C, and / or the preset pulse duration is greater than or equal to 8 seconds and less than or equal to 12 seconds.

[0125] In a possible implementation, the second open circuit voltage is the highest voltage rebounded after the pulse test.

[0126] In a possible implementation, the grouping module 603 is specifically used to calculate the mean of the self-discharge impedances of the battery cells of the same batch; the battery cells of the same batch are divided into a first category of battery cells and a second category of battery cells according to the relationship between the self-discharge impedances of the battery cells of the same batch and the mean; wherein the self-discharge impedance of the first category of battery cells is greater than or equal to the mean, and the self-discharge impedance of the second category of battery cells is less than the mean; according to the initial performance parameters of the first category of battery cells, the first category of battery cells are consistently grouped to obtain first category of shipped battery cells with consistent dynamic performance; wherein the initial performance parameters of the first category of shipped battery cells are all within the first preset parameter range; according to the initial performance parameters of the second category of battery cells, the second category of battery cells are consistently grouped to obtain second category of shipped battery cells with consistent dynamic performance; wherein the initial performance parameters of the second category of shipped battery cells are all within the second preset parameter range.

[0127] Figure 7 It is a structural schematic diagram of an electronic device provided in an embodiment of the present application.

[0128] For example, Figure 7 As shown, the electronic device includes: a memory 701 and a processor 702, wherein the memory 701 stores executable program code, and the processor 702 is used to call and execute the executable program code to perform a method for cell screening.

[0129] In this embodiment, the electronic device can be divided into functional modules according to the above method example. For example, the functional modules can be corresponding, or two or more functions can be integrated into one processing module. The above integrated module can be implemented in the form of hardware. It should be noted that the division of modules in this embodiment is schematic and is only a logical function division. There may be other division methods in actual implementation.

[0130] In the case of using corresponding functional division function modules, the electronic device may include: a first acquisition module, a second acquisition module and a grouping module, etc. It should be noted that all relevant contents of the steps involved in the above method embodiment can be referred to the functional description of the corresponding function modules, which will not be repeated here.

[0131] The electronic device provided in this embodiment is used to execute the above-mentioned method for screening battery cells, and thus can achieve the same effect as the above-mentioned implementation method.

[0132] In the case of an integrated unit, the electronic device may include a processing module and a storage module. The processing module may be used to control and manage the actions of the electronic device. The storage module may be used to support the electronic device in executing mutual program codes and data.

[0133] The processing module may be a processor or a controller, which may implement or execute the exemplary logic blocks, modules and circuits represented in conjunction with the disclosure of the present application. The processor may also be a combination that implements computing functions, such as a combination of one or more microprocessors, a combination of digital signal processing (DSP) and a microprocessor, etc. The storage module may be a memory.

[0134] This embodiment also provides a computer-readable storage medium, in which a computer program code is stored. When the computer program code is run on a computer, the computer executes the above-mentioned related method steps to implement a method for cell screening in the above-mentioned embodiment.

[0135] This embodiment further provides a computer program product. When the computer program product is run on a computer, the computer is enabled to execute the above-mentioned related steps to implement a method for cell screening in the above-mentioned embodiment.

[0136] In addition, the electronic device provided in the embodiments of the present application may specifically be a chip, a component or a module, and the electronic device may include a connected processor and a memory; wherein the memory is used to store instructions, and when the electronic device is running, the processor may call and execute instructions so that the chip executes a method for cell screening in the above-mentioned embodiments.

[0137] Among them, the electronic device, computer-readable storage medium, computer program product or chip provided in this embodiment are all used to execute the corresponding methods provided above. Therefore, the beneficial effects that can be achieved can refer to the beneficial effects in the corresponding methods provided above and will not be repeated here.

[0138] Through the description of the above implementation methods, technical personnel in the relevant field can understand that for the convenience and simplicity of description, only the division of the above-mentioned functional modules is used as an example. In actual applications, the above-mentioned functions can be assigned to different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above.

[0139] In the embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of modules or units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another device, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0140] The above contents are only specific implementation methods of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for screening battery cells, characterized in that: The method comprises the steps of: S10, obtaining initial performance parameters of the battery cells of the same batch; S20, obtaining the self-discharge impedance of the battery cells of the same batch; S30, grouping the battery cells of the same batch according to their initial performance parameters and the self-discharge impedance to obtain battery cells for shipment with consistent dynamic performance.

2. The method according to claim 1, characterized in that The step S20 comprises: S201, obtaining a first open circuit voltage and a second open circuit voltage during a K value test of the battery cell; wherein the first open circuit voltage is measured after a first normal temperature rest, and the second open circuit voltage is measured after a second normal temperature rest; S202, after the first normal temperature resting and before the second normal temperature resting, performing a pulse test on the battery cell according to a preset charging rate and a preset pulse duration, and measuring the measured capacity of the battery cell after the pulse test; S204, calculating the capacitance of the battery cell according to the voltage difference between the first open circuit voltage and the second open circuit voltage and the measured capacity; S205, determining a relaxation time constant according to the first open circuit voltage, a first test time point at which the first open circuit voltage is measured, the second open circuit voltage, and a second test time point at which the second open circuit voltage is measured; S206: Using the ratio of the relaxation time constant to the capacitance as the self-discharge impedance of the battery cell.

3. The method according to claim 2, characterized in that The step S205 includes: S2051, calculating the logarithmic value of the first open circuit voltage, and determining a first target coordinate point with the first test time point as the abscissa and the logarithmic value of the first open circuit voltage as the ordinate; S2052, calculating the logarithmic value of the second open circuit voltage, and determining a second target coordinate point with the second test time point as the abscissa and the logarithmic value of the second open circuit voltage as the ordinate; S2053, performing curve fitting according to the first target coordinate point and the second target coordinate point to obtain a relaxation voltage-time curve; S2054: Determine the negative inverse of the slope of the relaxation voltage-time curve as the relaxation time constant.

4. The method according to claim 3, characterized in that After S202, the method further includes: S203, within a preset time after the pulse test, placing the battery cell on a test channel and measuring the voltage of the battery cell at N sampling time points to obtain N sampling voltages corresponding to the N sampling time points, wherein the preset time is greater than or equal to 1 minute and less than or equal to 4 minutes, and N is greater than 3; The S2053 includes: Calculating the logarithmic values ​​of the sampled voltages corresponding to the N sampling time points to obtain N third coordinate points with the sampling time points as abscissas and the logarithmic values ​​of the sampled voltages as ordinates; Curve fitting is performed according to the N third coordinate points, the first target coordinate point, and the second target coordinate point to obtain a relaxation voltage-time curve.

5. The method according to claim 2, characterized in that: The preset charging rate is greater than or equal to 0.5C and less than or equal to 1C, and / or the preset pulse duration is greater than or equal to 8 seconds and less than or equal to 12 seconds.

6. The method according to claim 2, characterized in that The second open circuit voltage is the highest voltage rebounded after the pulse test.

7. The method according to any one of claims 1 to 6, characterized in that: The step S30 includes: Calculating the mean value of the self-discharge impedance of the battery cells of the same batch; According to the relationship between the self-discharge impedance of the battery cells of the same batch and the mean value, the battery cells of the same batch are divided into a first type of battery cells and a second type of battery cells; wherein the self-discharge impedance of the first type of battery cells is greater than or equal to the mean value, and the self-discharge impedance of the second type of battery cells is less than the mean value; According to the initial performance parameters of the first type of battery cells, the first type of battery cells are grouped for consistency to obtain the first type of shipped battery cells with consistent dynamic performance; wherein the initial performance parameters of the first type of shipped battery cells are all within a first preset parameter range; According to the initial performance parameters of the second type of battery cells, the second type of battery cells are grouped for consistency to obtain second type of shipped battery cells with consistent dynamic performance; wherein the initial performance parameters of the second type of shipped battery cells are all within a second preset parameter range.

8. A device for screening battery cells, characterized in that: The device comprises: A first acquisition module is used to acquire initial performance parameters of battery cells of the same batch; A second acquisition module is used to acquire the self-discharge impedance of the battery cells of the same batch; The grouping module is used to group the battery cells of the same batch according to their initial performance parameters and the self-discharge impedance, so as to obtain the battery cells for shipment with consistent dynamic performance.

9. An electronic device, characterized in that: The electronic device comprises: A memory for storing executable program codes; A processor, configured to call and run the executable program code from the memory, so that the electronic device executes the method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed, the method according to any one of claims 1 to 7 is implemented.

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