A lithium ion battery self-discharge screening method and device

Abstract

The application relates to the technical field of batteries and discloses a lithium ion battery self-discharge screening method and device. The method comprises the following steps: charging each to-be-tested battery to the same target charging voltage; performing aging treatment on the to-be-tested battery according to a preset aging process; detecting the open-circuit voltage test value of the to-be-tested battery after the aging treatment; and screening out a self-discharge poor battery according to the open-circuit voltage test value and a preset open-circuit voltage standard value. In the embodiment of the application, each to-be-tested battery is pre-charged, so that the open-circuit voltages of the to-be-tested batteries remain in a substantially consistent state before the aging treatment; then, the to-be-tested batteries are subjected to the aging treatment; finally, one open-circuit voltage test is performed, and the self-discharge poor battery can be screened out. Compared with the traditional mode, the two open-circuit voltage tests are simplified into one open-circuit voltage test in the embodiment of the application, the screening period is greatly shortened, the screening efficiency is improved, and the cost is reduced.

Description

Technical Field

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

[0002] Self-discharge is a crucial indicator of lithium battery performance, significantly impacting battery lifespan and consistency. Using batteries with inconsistent self-discharge within the same module or system will lead to increasingly poor consistency over time, ultimately resulting in substandard performance and lifespan. Therefore, accurate self-discharge testing is essential.

[0003] Currently, the commonly used self-discharge testing methods include the following two:

[0004] The first method is the K-value screening method: An open-circuit voltage test is performed on each battery before and after a period of storage. The self-discharge level of each battery is determined based on the difference between the two open-circuit voltage test results. This method requires two open-circuit voltage tests, and the results of the two tests for each battery must be matched one-to-one.

[0005] The second method is the voltage screening method: After performing the first open-circuit voltage test on each battery to be tested, they are divided into groups. After being left for a period of time, the second open-circuit voltage test is performed on each grouped battery to be tested. The batteries with high self-discharge can be screened based solely on the results of the second open-circuit voltage test.

[0006] Compared with the K-value screening method, the voltage screening method described above does not require matching the two open-circuit voltage test results of each battery under test one by one. However, it still requires two open-circuit voltage tests, which makes the self-discharge screening cycle too long, resulting in lower battery production efficiency and higher production costs. Summary of the Invention

[0007] The purpose of this invention is to provide a method and apparatus for screening the self-discharge of lithium-ion batteries, so as to solve the problem of excessively long screening cycles in existing screening methods.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] A method for screening the self-discharge of lithium-ion batteries, comprising the following steps:

[0010] Charge each battery under test to the same target charging voltage;

[0011] Each battery under test was aged according to the preset aging process.

[0012] Test the open-circuit voltage of each battery under test after aging treatment.

[0013] Based on the open-circuit voltage test value and the preset open-circuit voltage standard value, batteries with poor self-discharge are selected from each battery to be tested.

[0014] Optionally, charging each battery under test to the same target charging voltage includes:

[0015] Each battery under test is charged with constant current and constant voltage at least twice in sequence, and each time the battery under test is charged to the target charging voltage. The charging current used in each charging step decreases sequentially.

[0016] Optionally, the constant current and constant voltage charging of each battery under test in at least two separate operations includes: charging at a standard temperature,

[0017] First, the battery under test is charged with constant current and constant voltage using the first charging current to the target charging voltage and the first cutoff current.

[0018] Then, using a second charging current, the battery under test is charged at a constant current and constant voltage to the target charging voltage and the second cutoff current;

[0019] Finally, a third charging current is used to charge the battery under test to the target charging voltage and the third cutoff current using a constant current and constant voltage.

[0020] The first charging current, the second charging current, and the third charging current decrease sequentially, as do the first cutoff current, the second cutoff current, and the third cutoff current.

[0021] Optionally, the method of performing constant current and constant voltage charging on each battery under test in at least two separate cycles further includes: after the battery under test has completed the current charging, it is left to stand for a preset time before the next charging is performed.

[0022] Optionally, the first charging current is 0.75C±0.25C, the second charging current is 0.1C±0.05C, and the third charging current is 0.05C±0.02C.

[0023] Optionally, the first cutoff current is 0.05C, the second cutoff current is 0.02C, and the third cutoff current is 0.01C.

[0024] Optionally, the aging process performed on each battery under test according to a preset aging process includes:

[0025] First, each battery under test was placed in a high-temperature environment for a first time, and then placed in a room-temperature environment for a second time.

[0026] Optionally, the temperature of the high-temperature environment is 45℃±2℃, and the temperature of the normal-temperature environment is 25℃±2℃;

[0027] The first duration is 10-15 days, and the second duration is 1-2 days.

[0028] Optionally, the target charging voltage is specifically a preset shipping voltage V1;

[0029] The open-circuit voltage standard value U 标准 It is calculated based on the shipment voltage V1, the battery self-discharge efficiency K, and the battery high-temperature aging time T.

[0030] A lithium-ion battery self-discharge screening device for implementing the lithium-ion battery self-discharge screening method described in any one of the above claims, comprising:

[0031] The charging unit is used to charge each battery under test to the same target charging voltage.

[0032] The aging unit is used to perform aging treatment on each battery under test according to a preset aging process.

[0033] The voltage testing unit is used to detect the open-circuit voltage of each battery under test after aging treatment.

[0034] The screening unit is used to screen out batteries with poor self-discharge from each of the batteries to be tested based on the open-circuit voltage test value and the preset open-circuit voltage standard value.

[0035] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0036] In this embodiment of the invention, each battery under test is pre-charged to ensure that its open-circuit voltage remains essentially consistent before aging treatment. Then, each battery is aged, and finally, an open-circuit voltage test is performed to screen out batteries with poor self-discharge. Compared to traditional K-value screening methods and voltage screening methods, this embodiment simplifies two open-circuit voltage tests into one, significantly shortening the screening cycle, improving screening efficiency, and reducing costs. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 A flowchart of a lithium-ion battery self-discharge screening method provided in an embodiment of the present invention.

[0039] Figure 2 This is a scatter plot of charging voltages for different charging methods provided in embodiments of the present invention. Detailed Implementation

[0040] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0041] To address the issues of long screening cycles and high costs associated with existing self-discharge screening schemes that require two open-circuit voltage tests on the battery under test, this invention provides a lithium-ion battery self-discharge screening method and apparatus. This method simplifies the open-circuit voltage test to a single test, eliminating the need for separate battery selection, thereby shortening the overall self-discharge screening cycle, improving production efficiency, and reducing production costs.

[0042] Please see Figure 1 The lithium-ion battery self-discharge screening method provided in this embodiment of the invention specifically includes the following steps:

[0043] Step 101: Charge each battery under test to the same target charging voltage.

[0044] In this step, since all the batteries under test are charged to a uniform target charging voltage, it can be ensured that the voltage state of each battery under test remains basically consistent before the aging process.

[0045] Step 102: Perform aging treatment on each battery under test according to the preset aging process.

[0046] Step 103: Detect the open-circuit voltage of each battery after aging treatment.

[0047] It is understandable that, since the self-discharge efficiency of each battery under test may differ, the open-circuit voltage test values ​​of each battery under test will naturally differ after undergoing the same aging treatment.

[0048] Step 104: Based on the open circuit voltage test value and the preset open circuit voltage standard value, select the batteries with poor self-discharge from each battery to be tested.

[0049] Specifically, if the open-circuit voltage test value of the battery under test is lower than the open-circuit voltage standard value by a preset amount, the battery under test can be identified as a battery with poor self-discharge.

[0050] In summary, this invention pre-charges each battery under test, ensuring that their open-circuit voltages remain essentially consistent before aging. Then, each battery undergoes aging, followed by a single open-circuit voltage test, allowing for the screening of batteries with poor self-discharge. Compared to traditional K-value and voltage-based screening methods, this invention simplifies two open-circuit voltage tests into a single test, significantly shortening the screening cycle, improving efficiency, and reducing costs.

[0051] To reduce battery polarization problems caused by charging (the phenomenon that the potential deviates from the equilibrium potential when current flows through the battery is called battery polarization), in step 101, each battery under test is charged to the same target charging voltage. This may include: performing constant current and constant voltage charging on each battery under test in at least two separate steps, and charging each battery under test to the target charging voltage each time, with the charging current used in each charging step decreasing sequentially.

[0052] This method, through multiple charging cycles, allows the actual voltage of the battery under test after charging to be closer to the target charging voltage.

[0053] For example, each battery under test is charged with constant current and constant voltage at least twice in sequence, specifically including: at a standard temperature (e.g., 25℃±2℃),

[0054] First, the battery under test is charged with constant current and constant voltage using the first charging current to the target charging voltage and the first cutoff current.

[0055] Then, the second charging current is used to charge the battery under test with constant current and constant voltage until the target charging voltage and the second cutoff current are reached;

[0056] Finally, the third charging current is used to charge the battery under test to the target charging voltage and the third cutoff current using constant current and constant voltage.

[0057] Among them, the first charging current, the second charging current and the third charging current show a decreasing trend in sequence, and the first cutoff current, the second cutoff current and the third cutoff current show a decreasing trend in sequence.

[0058] This example involves three charging cycles. The smaller the charging current, the smaller the battery polarization. After the first constant-voltage charging, the voltage is relatively dispersed due to the presence of polarization. Two additional low-current charging cycles are added to continue charging the batteries with low voltage from the first charging cycle to the target charging voltage. This reduces the voltage difference between batteries after charging, thus allowing the battery under test to be charged to the target charging voltage more quickly and effectively. Figure 2The image shows a comparison of voltages after one constant-voltage charging cycle and three constant-voltage charging cycles. Figure 2 It is evident that the voltages during the three constant-voltage charging cycles are more concentrated, suggesting that the open-circuit voltages are consistent.

[0059] When using a multi-stage charging method for the batteries under test, to further ensure charging efficiency, the method of performing constant current and constant voltage charging on each battery at least twice in sequence also includes: after each charging cycle, allowing the battery to rest for a preset time (e.g., 2 hours) before the next charging cycle. This way, the battery can reach a stable voltage state before entering the next charging cycle, thus achieving a better charging effect.

[0060] For example, the first charging current is 0.75C ± 0.25C, the second charging current is 0.1C ± 0.05C, and the third charging current is 0.05C ± 0.02C. The first cutoff current is 0.05C, the second cutoff current is 0.02C, and the third cutoff current is 0.01C.

[0061] In step 102 above, each battery under test is aged according to a preset aging process, including: first, placing each battery under test in a high-temperature environment for a first duration, and then placing each battery under test in a room-temperature environment for a second duration.

[0062] The temperature for the high-temperature environment can be selected as 45℃±2℃, and the temperature for the normal-temperature environment can be selected as 25℃±2℃; the first duration is 10-15 days, and the second duration is 1-2 days.

[0063] Furthermore, the target charging voltage mentioned in step 101 can be any set value. For ease of management, it can usually be set to a preset shipping voltage V1. Based on this, the open-circuit voltage standard value U mentioned in step 104... 标准 Specifically, it is calculated based on the shipment voltage V1, the battery self-discharge efficiency K (which can be obtained from experimental testing), and the battery high-temperature aging time T. The calculation formula is as follows: U 标准 =V1-K*T.

[0064] Based on the same inventive concept, this invention also provides a lithium-ion battery self-discharge screening device, specifically comprising:

[0065] The charging unit is used to charge each battery under test to the same target charging voltage.

[0066] The aging unit is used to perform aging treatment on each battery under test according to a preset aging process.

[0067] The voltage testing unit is used to detect the open-circuit voltage of each battery under test after aging treatment.

[0068] The screening unit is used to screen out batteries with poor self-discharge from each battery under test based on the open-circuit voltage test value and the preset open-circuit voltage standard value.

[0069] The lithium-ion battery self-discharge screening device provided in this embodiment of the invention is used to implement the above-mentioned lithium-ion battery self-discharge screening method, which can effectively shorten the battery self-discharge screening cycle, improve screening efficiency, and reduce costs.

[0070] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of self-discharge screening of lithium-ion batteries, characterized in that, The method comprises the steps of: charging each of the to-be-tested batteries to the same target charging voltage; aging each of the to-be-tested batteries according to a preset aging process; detecting the open-circuit voltage test value of each of the to-be-tested batteries after the aging treatment; selecting a self-discharge poor battery from each of the to-be-tested batteries according to the open-circuit voltage test value and a preset open-circuit voltage standard value; The step of charging each of the to-be-tested batteries to the same target charging voltage comprises: charging each of the to-be-tested batteries in at least two times in a sequence, and charging each of the to-be-tested batteries to the target charging voltage each time, and the charging current used in each charging step is reduced in turn; The step of charging each of the to-be-tested batteries in at least two times in a sequence comprises: firstly, charging the to-be-tested battery to the target charging voltage and a first cut-off current by using a first charging current in constant current and constant voltage charging; secondly, charging the to-be-tested battery to the target charging voltage and a second cut-off current by using a second charging current in constant current and constant voltage charging; finally, charging the to-be-tested battery to the target charging voltage and a third cut-off current by using a third charging current in constant current and constant voltage charging; The first charging current, the second charging current and the third charging current are reduced in turn, and the first cut-off current, the second cut-off current and the third cut-off current are reduced in turn; The method further comprises: after completing the charging of the to-be-tested battery, the to-be-tested battery is first placed for a preset time, and then the next charging is performed.

2. The lithium-ion battery self-discharge screening method of claim 1, wherein, The first charging current is 0.75C±0.25C, the second charging current is 0.1C±0.05C, and the third charging current is 0.05C±0.02C.

3. The lithium-ion battery self-discharge screening method of claim 1, wherein, The first cut-off current is 0.05C, the second cut-off current is 0.02C, and the third cut-off current is 0.01C.

4. The lithium-ion battery self-discharge screening method of claim 1, wherein, The step of aging each of the to-be-tested batteries according to a preset aging process comprises: firstly, placing each of the to-be-tested batteries in a high-temperature environment for a first time, and then placing each of the to-be-tested batteries in a normal-temperature environment for a second time.

5. The lithium-ion battery self-discharge screening method of claim 4, wherein, The temperature of the high-temperature environment is 45℃±2℃, and the temperature of the normal-temperature environment is 25℃±2℃. The first time is 10 days-15 days, and the second time is 1 day-2 days.

6. The lithium-ion battery self-discharge screening method of claim 1, wherein, The target charging voltage is specifically a preset delivery voltage V1. The open-circuit voltage standard value U 标准 is obtained according to the shipment voltage V1, the battery self-discharge efficiency K, and the battery high-temperature aging time T.

7. A lithium ion battery self-discharge screening device for implementing the method of any one of claims 1 to 6, characterized in that, The method comprises: a charging unit configured to charge each of the to-be-tested batteries to the same target charging voltage; an aging unit configured to age each of the to-be-tested batteries according to a preset aging process; a voltage test unit configured to detect the open-circuit voltage test value of each of the to-be-tested batteries after the aging treatment; a selection unit configured to select a self-discharge poor battery from each of the to-be-tested batteries according to the open-circuit voltage test value and a preset open-circuit voltage standard value.

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