Method for improving self-discharge screening capability

Abstract

The invention relates to a method for improving self-discharge screening capability, and relates to the technical field of lithium batteries. The method comprises the following steps: carrying out primary screening on a battery by adopting an overall differential pressure method; the qualified batteries subjected to primary screening are subjected to secondary screening through a single-tray standard deviation method, the K value mean value of all the batteries on a single tray is calculated and obtained, the single-tray standard deviation method judgment scheme is as follows: standard deviation multiple = (K value-single-tray K value mean value) / standard deviation, the threshold value of the standard deviation multiple is-0.008-0.008, and the threshold value of the single-tray K value mean value is-0.008-0.008. The batteries of which the standard deviation multiples are within the range are judged as qualified batteries; and establishing a reworking process for the screened unqualified batteries, performing re-determination according to a long-term K value standard after standing, re-dividing the unqualified batteries passing the determination into qualified batteries and transferring to the next process, and determining the batteries which do not pass the determination as the unqualified batteries. The lithium battery self-discharge screening method and device have the advantages that the abnormal batteries can be screened out more accurately, and the probability of occurrence of mistaken killing and missing killing in lithium battery self-discharge screening is reduced.

Description

Technical Field

[0001] This application relates to the technical field of lithium batteries, and particularly to a method for improving the self-discharge screening ability. Background Art

[0002] A lithium battery is a secondary battery with a lithium metal or lithium alloy as the negative electrode material and a non-aqueous electrolyte solution, which has the advantages of high energy density, long cycle life, low self-discharge rate, etc., and is widely used in fields such as consumer electronics, electric vehicles, and energy storage systems; the self-discharge of a lithium battery refers to the phenomenon that the battery spontaneously reduces its power due to internal chemical reactions or physical factors when not connected to a load. The dissolution of transition metal ions in the positive electrode material, the reaction between the negative electrode material and the electrolyte, and the decomposition of the electrolyte may all cause self-discharge; the self-discharge of a lithium battery may lead to safety hazards such as its own capacity loss and deterioration of the battery pack performance. Therefore, the self-discharge detection of lithium batteries is crucial.

[0003] In the prior art, the overall pressure difference method is mostly used for the self-discharge detection of lithium batteries. The K-value determination is relatively simple and is suitable for the abnormal screening of the overall sample, but it is insufficient for the discrete points and re-capacitance of some parts. Moreover, the open-circuit voltage of the battery is greatly affected by measurement systems such as the test environment temperature, battery SOC, and equipment accuracy. Therefore, the method of determining the self-discharge abnormality of the battery only by the pressure difference cannot effectively and accurately screen out abnormal batteries, and there are certain misclassifications and omissions, so it needs to be improved. Summary of the Invention

[0004] In order to more accurately screen out abnormal batteries and reduce the probability of misclassifications and omissions in the self-discharge screening of lithium batteries, this application provides a method for improving the self-discharge screening ability.

[0005] A method for improving the self-discharge screening ability provided by this application adopts the following technical solution:

[0006] A method for improving the self-discharge screening ability includes the following steps:

[0007] S1: Use the overall pressure difference method to conduct a primary screening of the battery, and preliminarily screen out the qualified batteries and unqualified batteries of the battery;

[0008] S2: Use the single-tray standard deviation method to conduct a secondary screening of the qualified batteries that have undergone the primary screening, calculate and obtain the average K-value of all batteries on a single tray. The determination scheme of the single-tray standard deviation method: standard deviation multiple = (K-value - average K-value of a single tray) / standard deviation. The threshold of the standard deviation multiple is -0.008 - 0.008. The batteries with the standard deviation multiple within this range are determined as qualified batteries, and those outside this range are still determined as unqualified batteries;

[0009] S3: Transfer the qualified batteries selected in steps S1 and S2 to the next process.

[0010] S4: Establish a rework process for the unqualified batteries selected in steps S1 and S2. After standing, rejudge according to the long-term K value standard. Reclassify the unqualified batteries that pass the judgment as qualified batteries and transfer them to the next process. Determine the batteries that do not pass the judgment as unqualified batteries.

[0011] By adopting the above technical solution, when screening the self-discharge of batteries, the overall pressure difference method and the single-tray standard deviation method are adopted successively, which can reduce the influence of test environment temperature, battery SOC, equipment accuracy, etc. on the test results, so as to reduce the missed killing rate of battery self-discharge screening; in step S4, the suspected over-killed batteries can be reworked to re-detect the batteries, reducing the over-killing rate, thereby improving the accuracy of the self-discharge screening process.

[0012] Preferably, in step S1, the core capacity of the batteries participating in the initial screening > 326 Ah.

[0013] By adopting the above technical solution, it is ensured that the initial quality of each core participating in the test screening is qualified, and thus the accuracy of subsequent steps can be effectively improved.

[0014] Preferably, in step S2, the number of batteries on a single tray is 24.

[0015] By adopting the above technical solution, the number of cores is 24, which is moderate. On the one hand, it can improve the accuracy of the K value average, and on the other hand, it can also improve the overall working efficiency of the battery self-discharge screening process.

[0016] Preferably, in step S4, the standing time of the unqualified batteries is 15 - 30 days.

[0017] By adopting the above technical solution, setting the standing time to 15 - 30 days, the cycle is moderate, which can give the staff enough observation time to improve the probability of calculation errors of the long-term K value caused by too short or too long standing time.

[0018] Preferably, the empirical coefficient for calculating the long-term K value standard in step S4 is that the voltage drop during standing is less than or equal to 9 mv.

[0019] By adopting the above technical solution, for the problem of uncertain long-term K values of different models of batteries, the empirical coefficient for calculating the long-term K value standard is determined, which can judge the self-discharge situation of the batteries based on the observable actual data to reduce the over-killing rate.

[0020] Preferably, steps S1 - S4 are carried out in a workshop with temperature control of 25 ± 2°C.

[0021] By adopting the above technical solution, the influence of the ambient temperature on the test and screening results can be further reduced. The temperature is maintained within a relatively stable and suitable range, which can effectively improve the screening accuracy of the whole process and reduce the error rate.

[0022] In summary, the present application includes at least one of the following beneficial technical effects:

[0023] 1. When performing battery self-discharge screening, the overall pressure difference method and the single-tray standard deviation method are successively adopted, which can reduce the influence of the test environment temperature, battery SOC, equipment accuracy, etc. on the test results, so as to reduce the missed killing rate of battery self-discharge screening; through step S4, the batteries suspected of over-killing can be reworked to re-detect the batteries, reducing the over-killing rate, thereby improving the accuracy of the self-discharge screening process;

[0024] 2. The present application adopts three steps in total: the overall pressure difference method, the single-tray standard deviation method and the rework process, which strengthens the accuracy of K value selection to achieve the goal of cost reduction and efficiency improvement;

[0025] 3. The core capacity of each battery participating in the test is greater than 326 Ah, which can ensure that the initial quality of each core participating in the test and screening is qualified, and further effectively improve the accuracy of subsequent steps;

[0026] 4. The number of cores is 24, which is moderate. On the one hand, it can improve the accuracy of the average K value, and on the other hand, it can also improve the overall working efficiency of the battery self-discharge screening process;

[0027] 5. The static time is set to 15 - 30 days, and the cycle is moderate, which can give the staff enough observation time to improve the probability of long-term K value calculation errors caused by too short or too long static time. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a flowchart of a method for improving the self-discharge screening ability according to an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The following will further elaborate on the present application in conjunction with the attached Figure 1 for a more detailed description of the present application.

[0030] An embodiment of the present application discloses a method for improving the self-discharge screening ability. Referring to Figure 1 , it includes the following steps:

[0031] S1: The overall pressure difference method is used to conduct a preliminary screening of the batteries, and the qualified and unqualified batteries of the batteries are preliminarily screened out.

[0032] Specifically, the cell capacity of the battery for the initial screening needs to be greater than 326 Ah to ensure the accuracy of the initial screening and the results of subsequent other processes; in this embodiment, the overall pressure difference method is to measure the voltage of the battery twice, and the time difference between the two voltage measurements is fixed. The K value = the difference between the two measured voltages / the time difference of the measurement.

[0033] S2: Use the single-tray standard deviation method to perform a secondary screening on the qualified batteries that have undergone the initial screening, calculate and obtain the average value of the K values of all the batteries on a single tray. The judgment scheme of the single-tray standard deviation method: standard deviation multiple = (K value - average K value of a single tray) / standard deviation. The threshold of the standard deviation multiple is -0.008 - 0.008. The batteries with the standard deviation multiple within this range are judged as qualified batteries, and vice versa, they continue to be judged as unqualified batteries.

[0034] Specifically, the number of voltages tested on a single tray is 24 to improve the accuracy of the test results. Among them, in the calculation formula of the standard deviation multiple, the standard deviation fluctuates based on the K value results of the currently measured 24 cells. The batteries with the calculated results between -0.008 - 0.008 are judged as qualified batteries. The cells that meet the preset values calculated by the overall pressure difference method and the single-tray standard deviation method have high accuracy and can effectively improve the accuracy of the self-discharge screening.

[0035] S3: Transfer the qualified batteries screened in step S1 and step S2 to the next process.

[0036] S4: Establish a rework process for the unqualified batteries screened in step S1 and step S2. After standing, rejudge according to the long-term K value standard. The unqualified batteries that pass the judgment are reclassified as qualified batteries and transferred to the next process, and the batteries that do not pass the judgment are determined as unqualified batteries.

[0037] Specifically, the standing time of the batteries in the rework process is 15 - 30 days. Among them, the calculation of the long-term K value changes due to different battery models, while the empirical coefficient of the long-term K value remains unchanged, that is, the voltage drop within the standing time is not more than 9 mv. After this step, the batteries over-killed by step S1 and step S2 can be detected again to reduce the error rate of the battery self-discharge screening process.

[0038] In the specific implementation process, steps S1 - S4 are all carried out in a workshop with a temperature control of 25 ± 2 °C to further reduce the influence of the ambient temperature on the test and screening results, and thus effectively improve the accuracy.

[0039] The implementation principle of a method for improving the self-discharge screening ability in an embodiment of this application is as follows: When performing battery self-discharge screening, the overall pressure difference method and the single-disk standard deviation method are successively adopted, which can reduce the influence of the test environment temperature, battery SOC, equipment accuracy, etc. on the test results, so as to reduce the missed killing rate of battery self-discharge screening; through step S4, the suspected over-killed batteries can be reworked to re-detect the batteries, reducing the over-killing rate, thereby improving the accuracy of the self-discharge screening process; this application adopts three steps in total, namely the overall pressure difference method, the single-disk standard deviation method and the rework process, strengthening the accuracy of K value selection to achieve the goal of cost reduction and efficiency improvement.

[0040] The above are all preferred embodiments of this application. Without limiting the protection scope of this application accordingly, therefore: All equivalent changes made according to the structure, shape, and principle of this application shall be covered within the protection scope of this application.

Claims

1. A method for improving self-discharge screening capability, characterized in that: It includes the following steps: S1: Use the overall pressure difference method to conduct a primary screening of the batteries, and preliminarily screen out the qualified and unqualified batteries of the batteries; S2: Use the single-tray standard deviation method to conduct a secondary screening of the qualified batteries that have undergone the primary screening, calculate and obtain the average K value of all the batteries on a single tray. The judgment scheme of the single-tray standard deviation method is: standard deviation multiple = (K value - average K value of a single tray) / standard deviation. The threshold of the standard deviation multiple is -0.008 - 0.

008. The batteries with the standard deviation multiple within this range are judged as qualified batteries, and vice versa, they are still judged as unqualified batteries; S3: Transfer the qualified batteries screened out in step S1 and step S2 to the next process; S4: Establish a rework process for the unqualified batteries screened out in step S1 and step S2. After standing, rejudge according to the long-term K value standard. The unqualified batteries that pass the judgment are reclassified as qualified batteries and transferred to the next process, and the batteries that do not pass the judgment are determined as unqualified batteries.

2. The method for improving self-discharge screening capability according to claim 1, characterized in that: In step S1, the core capacity of the batteries participating in the primary screening > 326 Ah.

3. A method for enhancing the self-discharge screening ability according to claim 1, characterized in that: In step S2, the number of batteries on a single tray is 24.

4. The method for improving self-discharge screening capability according to claim 1, characterized in that: In step S4, the standing time of the unqualified batteries is 15 - 30 days.

5. A method for improving the self-discharge screening ability according to claim 4, characterized in that: The empirical coefficient calculated by the long-term K value standard in step S4 is that the voltage drop during the standing period is less than or equal to 9 mv.

6. The method for improving self-discharge screening capability according to claim 1, characterized in that: Steps S1 - S4 are carried out in a workshop with a temperature control of 25 ± 2°C.

Images