A screening method for self-discharge abnormality of lithium ion battery
By using pre-formation voltage testing and accelerated screening steps, a correlation between the self-discharge magnitude of lithium-ion batteries and the pre-formation voltage was established. This solved the problem of excessively long self-discharge testing time in existing technologies, enabling rapid and reliable self-discharge screening and reducing the rejection rate.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- JIANGSU HIGEE ENERGY CO LTD
- Filing Date
- 2023-10-07
- Publication Date
- 2026-06-05
AI Technical Summary
Existing self-discharge testing methods for lithium-ion batteries are too time-consuming, making it difficult to quickly and reliably screen out batteries with abnormal self-discharge.
By establishing the correlation between the battery's self-discharge magnitude and the pre-formation voltage through pre-formation voltage testing, and combining this with accelerated screening steps, batteries with abnormal self-discharge are screened out. This includes voltage testing after standing and voltage drop calculation, and batteries with normal self-discharge are screened out.
It enables rapid and reliable screening of batteries with self-discharge abnormalities, reduces the defect rate, and improves production efficiency.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for screening abnormal self-discharge of lithium-ion batteries. Background Technology
[0002] Lithium-ion batteries have outstanding advantages such as high energy density, no memory effect, long cycle life, fast charging and discharging, and low self-discharge. They are widely used in energy storage fields such as portable devices, electric vehicles, and aerospace, and have a huge market demand.
[0003] To produce qualified batteries, strict control over the production process is crucial, including factors such as humidity, areal density, thickness, and self-discharge. Self-discharge is a particularly important parameter for lithium-ion batteries, typically tested after capacity grading. The testing method involves placing the battery at a specific temperature for a period of time, measuring the voltage before and after this period, and calculating the voltage drop (voltage difference). Batteries exceeding the voltage difference standard are considered to have excessive self-discharge. Current self-discharge testing methods take anywhere from 2-3 days to a week or even a month, which is quite time-consuming.
[0004] Therefore, there is an urgent need for a simple and rapid method for screening the self-discharge of lithium batteries, which can not only avoid the drawbacks of excessively long testing time, but also maintain the reliability of the test results. Summary of the Invention
[0005] The purpose of this invention is to provide a screening method for abnormal self-discharge of lithium-ion batteries, which can not only avoid the drawback of excessively long testing time, but also maintain the reliability of test results.
[0006] The technical solution adopted by this invention to solve the above problems is: a method for screening abnormal self-discharge of lithium-ion batteries, comprising the following steps:
[0007] (1) Voltage test: Test the voltage of the lithium-ion battery before formation;
[0008] (2) Result judgment: Based on the result of step (1), make a judgment: if the voltage before formation is ≥0.5V, the self-discharge of the battery is considered normal; if the voltage before formation is ≤0.2V, the self-discharge of the battery is considered abnormal; if 0.2 < voltage before formation <0.5V, the self-discharge of the battery is considered uncertain.
[0009] (3) Accelerated screening: For batteries with uncertain self-discharge size in step (2), accelerated testing is performed after capacity grading to screen out batteries with normal self-discharge size. The specific steps are as follows:
[0010] a. Adjust the battery to a very low SOC, then let it stand at 45℃ for 12 hours, test the voltage before and after standing, and calculate the self-discharge, i.e., the voltage drop.
[0011] b. If the voltage drop value is greater than the standard value, the self-discharge is considered abnormal; if the voltage drop value is less than or equal to the standard value, the self-discharge is considered normal.
[0012] c. Batteries with normal self-discharge levels are selected from the statistical data and can be shipped normally.
[0013] Additionally, the percentage of batteries with abnormal self-discharge is calculated as follows: if the number of batteries with abnormal self-discharge is 'a', and the total number of tested batteries is 'h', then the percentage of batteries with abnormal self-discharge is a / h. If a / h ≤ 0.5%, it is considered normal; if a / h > 0.5%, it is considered abnormal, and the cause of the abnormality needs to be analyzed promptly. All processes involving cutting and welding should be investigated, the cause identified, and the problem resolved to minimize losses.
[0014] Preferably, a verification process is also included, as follows:
[0015] (1) Randomly select a certain number of lithium-ion batteries, test their voltage before formation, and count the number of lithium-ion batteries in each voltage range according to the following conditions: voltage before formation ≥ 0.5V, voltage before formation < 0.5V, and voltage before formation ≤ 0.2V. Then test the voltage drop of the lithium-ion batteries in each voltage range after capacity grading and count the number of qualified voltage drops after capacity grading in each voltage range. The corresponding qualified voltage drop rates after capacity grading are obtained and recorded as follows:
[0016]
[0017] (2) If the voltage drop pass rate after capacity testing is ≥99% for lithium-ion batteries with a pre-formation voltage ≥0.5V and the voltage drop pass rate after capacity testing is ≤1% for batteries with a pre-formation voltage ≤0.2V, then the screening method for abnormal self-discharge of lithium-ion batteries is considered reliable; otherwise, it is unreliable.
[0018] Preferably, the settling time in step (3)a is ≥12h and the settling temperature is ≥45℃.
[0019] Preferably, the lithium-ion battery includes a pre-charge process.
[0020] More preferably, the preparation process of the lithium-ion battery is as follows: liquid injection, pre-charging, aging, formation, aging, and capacity testing.
[0021] Preferably, the lithium-ion battery has a SOC (State of Charge) of 1-7%, where SOC refers to the state of charge (electrical capacity). A fully charged battery is 100% SOC; the higher the SOC, the greater the electrical capacity. Lithium-ion batteries are most sensitive to voltage changes caused by self-discharge within the 1-7% SOC range, making this range the most efficient for selection.
[0022] Compared with the prior art, the advantages of the present invention are as follows:
[0023] The screening method for lithium-ion battery self-discharge abnormalities of the present invention establishes a correspondence between the battery pre-formation voltage and the self-discharge magnitude, which can predict (predict) the self-discharge magnitude after battery capacity grading. This correspondence can be applied to the production process of lithium-ion batteries, which can detect situations with a high proportion of self-discharge abnormalities in advance, analyze and solve problems in advance, and reduce the scrap or defect rate. Implementation
[0024] The present invention will be further described in detail below with reference to the embodiments.
[0025] Example 1
[0026] A method for screening lithium-ion batteries with abnormal self-discharge includes the following steps:
[0027] (1) Voltage test: Test the pre-formation voltage of 3000 cylindrical 18650-1.5Ah batteries (the batteries have a pre-charge process: current 75mA, time 5min);
[0028] (2) Result judgment: Based on the results of step (1), the following judgments are made: 2982 batteries have a voltage ≥ 0.5V before formation, so the self-discharge of these batteries is considered normal; 3 batteries have a voltage ≤ 0.2V before formation, so the self-discharge of these batteries is considered abnormal; 15 batteries have a voltage < 0.5V before formation, so the self-discharge of these batteries is considered uncertain.
[0029] (3) Accelerated screening: For the 15 batteries with uncertain self-discharge size in step (2), after the capacity grading (constant current charging at 0.75A to 3.65V, then constant voltage charging to 0.075A, and then constant current discharging at 0.75A to 2.5V), accelerated testing was performed to screen out batteries with normal self-discharge size. The specific steps are as follows:
[0030] a. Adjust the battery to 2% SOC, then let it stand at 45℃ for 12 hours. Test the voltage before and after standing, and calculate the self-discharge, i.e., the voltage drop.
[0031] b. If 8 batteries have a voltage drop value > the standard value (2.5mV), then these batteries are considered to have abnormal self-discharge; if 7 batteries have a voltage drop ≤ the standard 2.5mV, then these batteries are considered to have normal self-discharge.
[0032] c. Batteries with normal self-discharge levels selected through statistical analysis can be shipped normally.
[0033] (4) Proportion of abnormal self-discharge: The number of batteries with abnormal self-discharge is a=8+3=11, and the total number of all tested batteries is h=3000. Therefore, the proportion of abnormal self-discharge is a / h=0.37%. Since a / h=0.37%≤0.5%, it is considered normal.
[0034] Verification experiment:
[0035] The specific steps are as follows:
[0036] Of the 3000 batteries mentioned above, 1000 were randomly selected. Their voltages were measured and statistically converted to their initial voltage values. The self-discharge rate (voltage drop) of these batteries after capacity grading was also measured and statistically recorded as follows:
[0037]
[0038] (2) The voltage drop pass rate after capacity testing of 990 batteries with a pre-formation voltage ≥ 0.5V was 100%; and the voltage drop pass rate after capacity testing of 2 batteries with a pre-formation voltage ≤ 0.2V was 0%. Therefore, the screening method for abnormal self-discharge of lithium-ion batteries is considered reliable.
[0039] Example 2
[0040] A method for screening lithium-ion batteries with abnormal self-discharge includes the following steps:
[0041] (1) Voltage test: Test the pre-formation voltage of 3000 cylindrical 18650-1.2Ah batteries (the batteries have a pre-charge process: current 60mA, time 5min);
[0042] (2) Result judgment: Based on the results of step (1), the following judgments are made: 2970 batteries have a voltage ≥ 0.5V before formation, so the self-discharge of these batteries is considered normal; 5 batteries have a voltage ≤ 0.2V before formation, so the self-discharge of these batteries is considered abnormal; 25 batteries have a voltage < 0.5V before formation, so the self-discharge of these batteries is considered uncertain.
[0043] (3) Accelerated screening: For the 25 batteries with uncertain self-discharge size in step (2), after the capacity grading (0.6A constant current charging to 3.65V, then constant voltage charging to 0.06A, and then 0.6A constant current discharging to 2.5V), accelerated testing was carried out to screen out batteries with normal self-discharge size. The specific steps are as follows:
[0044] a. Adjust the battery to 2% SOC, then let it stand at 45℃ for 12 hours. Test the voltage before and after standing, and calculate the self-discharge, i.e., the voltage drop.
[0045] b. If 15 batteries have a voltage drop value greater than the standard value (2.5mV), then these batteries are considered to have abnormal self-discharge; if 10 batteries have a voltage drop value less than or equal to the standard 2.5mV, then these batteries are considered to have normal self-discharge.
[0046] c. Batteries with normal self-discharge levels selected through statistical analysis can be shipped normally.
[0047] (4) Proportion of abnormal self-discharge: The number of batteries with abnormal self-discharge is a=15+5=20, and the total number of all tested batteries is h=3000. Therefore, the proportion of abnormal self-discharge is a / h=0.67%. If a / h=0.67%>0.5%, it is considered abnormal and the cause needs to be analyzed and resolved.
[0048] Verification experiment:
[0049] The specific steps are as follows:
[0050] (1) Of the above 3000 batteries, 1000 were randomly selected, and their voltages were measured and converted to their initial voltage. The self-discharge rate (i.e., voltage drop) of these batteries after capacity grading was also measured and recorded as follows:
[0051]
[0052] (2) The voltage drop pass rate after capacity testing of 989 batteries with a pre-formation voltage ≥ 0.5V was 100%; and the voltage drop pass rate after capacity testing of 1 battery with a pre-formation voltage ≤ 0.2V was 0%. Therefore, the screening method for abnormal self-discharge of lithium-ion batteries is considered reliable.
[0053] In addition to the above embodiments, the present invention also includes other embodiments. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.
Claims
1. A method for screening abnormal self-discharge of lithium-ion batteries, characterized in that: Includes the following steps: (1) Voltage test: Test the voltage of the lithium-ion battery before formation; (2) Result judgment: Based on the result of step (1), make a judgment: if the voltage before formation is ≥0.5V, the self-discharge of the battery is normal; if the voltage before formation is ≤0.2V, the self-discharge of the battery is abnormal; if 0.2 < voltage before formation <0.5V, the self-discharge of the battery is uncertain. (3) Accelerated screening: For batteries with uncertain self-discharge size in step (2), accelerated testing is performed after capacity grading to screen out batteries with normal self-discharge size. The specific steps are as follows: a. Adjust the battery to a very low SOC, then let it stand, test the voltage before and after standing, and calculate the self-discharge, i.e., the voltage drop; b. If the voltage drop value is greater than the standard value, the self-discharge is considered abnormal; if the voltage drop value is less than or equal to the standard value, the self-discharge is considered normal. c. Select batteries with normal self-discharge levels from the statistical analysis and ship them out normally; The screening method for abnormal self-discharge of lithium-ion batteries also includes a verification process, as detailed below: (1) Randomly select a certain number of lithium-ion batteries, test the voltage before formation, and count the number of lithium-ion batteries in each voltage range according to the voltage before formation ≥ 0.5V, 0.2 < voltage before formation < 0.5V, and voltage before formation ≤ 0.2V. Then test the voltage drop of lithium-ion batteries after capacity grading in each voltage range and count the number of qualified voltage drops of lithium-ion batteries after capacity grading in each voltage range. The qualified voltage drop rate after capacity grading is obtained respectively. (2) If the voltage drop pass rate after capacity testing is ≥99% for lithium-ion batteries with a pre-formation voltage ≥0.5V and the voltage drop pass rate after capacity testing is ≤1% for batteries with a pre-formation voltage ≤0.2V, then the screening method for lithium-ion battery self-discharge abnormality is reliable; otherwise, it is unreliable.
2. The screening method for abnormal self-discharge of lithium-ion batteries according to claim 1, characterized in that: In step (3), the settling time is ≥12h and the settling temperature is ≥45℃.
3. The screening method for abnormal self-discharge of lithium-ion batteries according to claim 1, characterized in that: The lithium-ion battery includes a pre-charge process.
4. The screening method for abnormal self-discharge of lithium-ion batteries according to claim 3, characterized in that: The preparation process of the lithium-ion battery is as follows: liquid injection, pre-charging, aging, formation, aging, and capacity testing.
5. The screening method for abnormal self-discharge of lithium-ion batteries according to claim 1, characterized in that: The state of charge (SOC) of the lithium-ion battery is between 1% and 7%.