Lithium ion battery formation equal-capacity retest method

Abstract

The invention discloses a lithium ion battery formation equal-capacity retest method. A battery formation process is divided into a first test step and a retest step; when the formation process is carried out on the lithium battery in the first measurement step, if the formation process is abnormally finished, remeasurement is carried out through the remeasurement step; if the formation process is normally finished, the formation is finished; and when formation is carried out in the retest step, a starting node during retest is determined according to the abnormal end information of the first test step, and the work step is executed from the starting node. Compared with the prior art, the method has the advantages that the NG cell retest process for cell formation is automatically connected to the abnormal end point of the first test process, subsequent steps are continued after connection, the cell formation charging time is ensured to be consistent, the capacity consistency of formation first test and retest cells is also ensured, and the cell performance is improved.

Description

Technical Field

[0001] The present invention relates to the field of lithium battery production processes, and in particular to a lithium ion battery formation and equal capacity retesting method. Background Art

[0002] As lithium-ion batteries gain wider application prospects, the energy density and cycle life requirements for battery cells are becoming increasingly demanding. Formation, a key process in the lithium-ion battery production process, aims to form a stable SEI film on the negative electrode surface. The structure of the SEI film directly affects the battery's cycle life, stability, self-discharge, and safety. Furthermore, during the formation process, both the SEI film-forming reaction and side reactions generate gases, which must be exhausted as completely as possible. Inadequate exhaust during formation will result in further gas generation during subsequent charge and discharge processes, leading to cell bulging.

[0003] The capacity consistency of the charge during the formation process directly affects the SEI film stability and gas production of the battery cell, resulting in performance variations. However, due to equipment or cell problems, the initial formation process of the battery cell is often abnormal, and rework and retesting are inevitable. This results in differences in the capacity of the retested cell and the normal cell capacity.

[0004] Currently, mainstream manufacturers' formation and activation processes all use low-current constant-current charging, with cutoff conditions set at voltage or time (capacity). However, equipment or cell issues often cause cell rework and retesting. The SOC levels of retested cells vary, so the retest process often uses a voltage cutoff, charging the retested cells to the same voltage cutoff. This results in differences in the capacity of retested cells compared to normal cells. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a lithium-ion battery formation and equal capacity retesting method, which solves the problem that the capacity of reworked and retested cells is inconsistent with that of normal cells when the cells are formed and activated, ensures the consistency of the formed capacity of the cells, and improves the performance of the cells.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a lithium ion battery formation equal capacity retesting method, which divides the battery formation process into an initial test step and a retesting step;

[0007] When the lithium battery is subjected to a formation process in the first test step, if the formation process ends abnormally, retesting is performed through the retest step; if the formation process ends normally, the formation is completed;

[0008] When the retest step is formed, the starting node of the retest is determined according to the information of the abnormal end of the first test step and the work step is executed from the starting node.

[0009] In the first test step, the abnormal end time point is recorded. After the abnormal end time point is found during the retest, the formation step is continued from the end point of the abnormal event until the formation step is completed.

[0010] The lithium-ion formation process includes multiple steps, each of which is equipped with a corresponding parameter control strategy. The steps are controlled sequentially according to the preset steps to complete the formation process.

[0011] In the parameter control strategy for each step in the formation process, the parameter types include step time, voltage, current, and vacuum degree.

[0012] During the first test step, the battery cell is subjected to the first activation process, and the end condition of the charging step of the first test process is the time end or the capacity end.

[0013] When lithium-ion batteries are being formed, the MES system records the information of the abnormal end time point, including the time information from the abnormal end point to the start of the formation, battery cell capacity information, voltage information, current information, and energy information.

[0014] The work step control and work step parameters in the retest process are consistent with the initial test process.

[0015] After the retest process starts, the battery cell is left to stand until the abnormal time end point recorded during the first test is reached, and then the current step is executed from the abnormal time end point until all processes are completed.

[0016] During the retest process, the MES system is used to monitor the retest process. If an abnormality occurs in the retest process, the abnormal end time point is recorded, and the second retest is continued based on the abnormal end point of the first retest.

[0017] The advantages of the present invention are that: the retest process of the battery cell is automatically connected to the abnormal end point of the first test process, and the subsequent steps are continued after the connection, so as to ensure that the battery cell formation and charging time are consistent, that is, the capacity consistency of the first test and retested battery cells is ensured, and the battery cell performance is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The following is a brief description of the contents and symbols in the drawings of the present invention:

[0019] Figure 1 The figure is a flow chart of the capacity retest principle of the formed battery cell of the present invention. DETAILED DESCRIPTION

[0020] The specific implementation of the present invention will be further explained in detail below by describing the best embodiment with reference to the accompanying drawings.

[0021] This solution is mainly used in the field of lithium-ion battery formation. It targets retesting caused by abnormal problems in the formation process. By controlling the retesting process, the consistency of capacity is achieved. This solves the problem of inconsistent capacity between reworked and retested cells and normal cells during cell formation and activation, ensuring the consistency of cell formation capacity and improving cell performance.

[0022] This solution is suitable for lithium-ion battery formation and retesting cells, such as Figure 1 As shown, the present solution provides a lithium-ion battery formation equal capacity retesting method, including the abnormal end of the first formation charging of the battery cell, recording the abnormal end time point, and when retesting the formation, after finding the abnormal end point, continuing to execute the current step from this point until the process ends.

[0023] The formation of lithium-ion batteries is divided into the first test and the retest. The first test will set the formation steps according to the requirements of the formation. The formation step is completed after each step of the formation is completed. If the formation ends abnormally due to various reasons during the formation process, it is necessary to enter the retest process to retest the formation. The retest is a repeated step of the first test. The logic and parameters of each step in the retest step are the same as the first test. However, if the first test is repeated directly during the retest, the capacity of the battery cell after the retest will be inconsistent with the battery cell that has been formed by only the first test. The inconsistent battery cell will affect the results of subsequent OCV, DCR and other processes, causing misjudgment. Therefore, the method adopted by this solution is to record the information of the abnormal time point of formation, calculate the time interval from the start of the first test to the abnormal time point, and immediately put the battery in a static state after the retest starts until the abnormal time point corresponding to the time interval is reached. The formation step corresponding to the time point here continues to start, executes the corresponding step, and completes the remaining steps, thereby achieving the purpose of formation retest.

[0024] Table 1 shows the formation process flow chart. During execution, steps 1-5 are executed sequentially and controlled according to the formation parameters of each step until completion. Each step has corresponding parameters such as step time, voltage, current, and vacuum level.

[0025] Table 1 Formation process

[0026] Serial number Steps Time / min Voltage / mV Current / mA Vacuum degree / Kpa Remark Step 1 Shelved 1 / / / Step 2 Constant current charging 120 3400 0.05C -80 Deadline Step 3 Shelved 3 / / -80 Step 4 Constant current charging 60 3650 0.15C -80 Deadline Step 5 Shelved 2 / / -80 Step 6 Finish / / / /

[0027] like Figure 1 , the capacity retest process of the formed battery cell is as follows:

[0028] S1, the battery cell is activated for the first time;

[0029] S2. MES records the abnormal end point information, including acquisition time, capacity, voltage, current, energy and other information. The recording time is for reaching the abnormal point during retesting and then starting the next step. Before entering the retesting, the recorded capacity, voltage, current, energy and other information are used to determine whether the battery cells that failed the initial test need to be retested. The detection information provides a basis for determining whether the NG battery cells need to be retested. Not all NG battery cells need to be retested.

[0030] If the battery cell fails the first test during the formation process, the data recorded during the formation process will be checked to determine whether the failure is caused by a process interruption due to equipment problems. If not, the battery cell will be reviewed, disassembled, analyzed, or downgraded. If so, it means that the failure is caused by the measuring equipment during the first test. At this time, it is necessary to determine whether to retest based on the data recorded during the first test. If it is determined that the retest is started, the equal capacity retest process will be carried out according to the solution of this embodiment. Otherwise, the battery cell will be scrapped, downgraded, or disassembled for analysis. Whether to retest needs to be determined by the engineer's judgment and analysis based on the specific situation. For example, if the process is interrupted due to the formation equipment, it is necessary to retest. If the first test process is interrupted due to the battery cell, the cause needs to be investigated. For example, if the contact is poor due to dirt on the battery cell tab or pole surface, it is necessary to retest. If the process is interrupted due to an abnormal increase in the battery cell temperature, it is determined that retesting is not possible.

[0031] S3, perform formation and retesting process on the battery cell;

[0032] S4. When the retest process reaches the abnormal end point of the first test, the retest process starts to continue to execute the current step operation corresponding to the current moment;

[0033] S5. After the steps are completed according to the timing, the process ends.

[0034] For NG cells tested during the first formation test, MES records abnormal end point information, including acquisition time, capacity, voltage, current, energy, and other information;

[0035] The battery cells are subjected to a retesting process. The retesting process follows the same flow as the initial test process. This embodiment uses the negative pressure forming process as an example. The process steps are shown in Table 1.

[0036] For step S4, when the retest process reaches the abnormal end point of the first test, the retest process starts to continue to execute the current step operation; when the battery cell is retested, it continues to be re-made from the beginning of the process. From the beginning of the battery cell process to the end point of the first abnormality, no matter what step the battery cell reaches, it will be left at rest and no charging operation will be performed.

[0037] To further illustrate the process flow in Table 1, suppose a cell's initial formation test abnormally terminates 40 minutes into step 4, meaning the cell has already run for 164 minutes since the start of the process. If the cell is assessed as retestable, when the retest process is executed, after 164 minutes of rest, the cell reaches the abnormal end point of the initial test (i.e., 40 minutes into step 4). The process then automatically continues with the current charging step (i.e., charging begins 40 minutes after step 4) until the process is complete.

[0038] For step S5: the process ends. The retested OK cells flow into the next process, and the retested NG cells need to be reworked after evaluation. The second retest is based on the abnormal end point of the first retest. The judgment method of abnormal NG includes:

[0039] 1. Equipment abnormality causes the battery cell to be NG during the first test. If the equipment and the battery cell are in poor contact, the battery cell will sound an alarm and the process will be interrupted, which means the battery cell is NG.

[0040] 2. The equipment is normal. After the process is completed, the battery cell voltage or capacity is not within the required range. In this case, the battery cell is also considered NG abnormal.

[0041] Every time a battery cell fails, manual judgment is required on whether the battery cell needs or can be retested. The production control system MES is used to set the number of NG retests. When the number of NG retests for the same battery cell exceeds the set threshold, the formation equipment will issue an alarm. The number of retests can be set and controlled through MES.

[0042] Based on C=I*t (capacity=current*time), the present invention automatically connects the retest process for NG cells to the abnormal end point of the initial test process, and then continues with subsequent steps to ensure that the charging time of the cell formation is consistent, that is, the capacity consistency of the cells tested initially and retested during formation is guaranteed. This solves the problem of inconsistent capacity between reworked and retested cells and normal cells during cell formation activation, ensures capacity consistency between the cells tested initially and retested during formation, and improves cell performance.

[0043] Obviously, the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A lithium-ion battery formation and capacity retesting method, characterized in that: The battery formation process is divided into the first test step and the retest step; When the lithium battery is subjected to a formation process in the first test step, if the formation process ends abnormally, retesting is performed through the retest step; if the formation process ends normally, the formation is completed; When the retest step is formed, the starting node of the retest is determined according to the information of the abnormal end of the first test step and the work step is executed from the starting node.

2. A lithium-ion battery formation equal capacity retesting method as claimed in claim 1, characterized in that: In the first test step, the abnormal end time point is recorded. After the abnormal end time point is found during the retest, the formation step is continued from the end point of the abnormal event until the formation step is completed.

3. A lithium ion battery formation equal capacity retesting method as claimed in claim 1 or 2, characterized in that: The lithium-ion formation process includes multiple steps, each of which is equipped with a corresponding parameter control strategy. The steps are controlled sequentially according to the preset steps to complete the formation process.

4. A lithium-ion battery formation equal capacity retesting method as claimed in claim 3, characterized in that: In the parameter control strategy for each step in the formation process, the parameter types include step time, voltage, current, and vacuum degree.

5. A lithium ion battery formation equal capacity retesting method as claimed in claim 1 or 2, characterized in that: During the first test step, the battery cell is subjected to the first activation process, and the end condition of the charging step of the first test process is the time end or the capacity end.

6. A lithium ion battery formation equal capacity retesting method as claimed in claim 1 or 2, characterized in that: When lithium-ion batteries are being formed, the MES system records the information of the abnormal end time point, including the time information from the abnormal end point to the start of the formation, battery cell capacity information, voltage information, current information, and energy information.

7. A lithium ion battery formation equal capacity retesting method as claimed in claim 1 or 2, characterized in that: The work step control and work step parameters in the retest process are consistent with the initial test process.

8. A lithium ion battery formation equal capacity retesting method as claimed in claim 1 or 2, characterized in that: After the retest process starts, the battery cell is left to stand until the abnormal time end point recorded during the first test is reached, and then the current step is executed from the abnormal time end point until all processes are completed.

9. A lithium ion battery formation equal capacity retesting method as claimed in claim 1 or 2, characterized in that: During the retest process, the MES system is used to monitor the retest process. If an abnormality occurs in the retest process, the abnormal end time point is recorded, and the second retest is continued based on the abnormal end point of the first retest.

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