Method for screening battery cell formation and aging processes

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a method for screening a battery cell formation and aging process, which comprises the following steps: firstly, taking a plurality of battery cells subjected to capacity grading in the same material system, carrying out charge-discharge test by utilizing charge-discharge equipment consistent with a production line redischarge system, and analyzing voltage drop to obtain a stable voltage state of the battery cells in the material system; taking a part of production line battery cells, forming a part of the production line battery cells under different formation processes, aging the part of the production line battery cells under the same aging process, carrying out capacity grading to the stable voltage state obtained in the previous step, measuring voltage drop data, and taking the formation process corresponding to the battery cell with the minimum voltage drop as the optimal formation process of the battery cells of the material system; the other part of the battery cells are formed in the same formation process and aged in different aging processes, capacity grading is carried out to the stable voltage state obtained in the previous step, voltage drop data are measured, and the aging process corresponding to the battery cell with the minimum voltage drop is the optimal aging process of the battery cells of the material system.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a method for screening battery cell formation and aging processes. Background Art

[0002] Currently, the industry's method for screening different formation processes and high-temperature aging processes mainly uses laboratory ORT testing to evaluate performance. The testing time is long and batch testing is not possible. There is a lack of a rapid evaluation method for the production line. The present invention provides a method that can sensitively and quickly characterize battery cell performance, thereby quickly screening the optimal formation process and aging process for battery cells with a specified material system. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for screening the formation and aging processes of battery cells. After the battery cells are divided in capacity, the voltage drop of the battery cells stored for a certain period of time under the same stable voltage state is measured to quickly characterize the performance of the battery cells under different formation and aging process conditions, and then screen the optimal formation and aging processes for the battery cells of the material system.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for screening battery cell formation and aging processes, comprising the following steps: S1: Take several battery cells with the same material system and place them on a charging and discharging device for testing. The charging and discharging mode of the charging and discharging device is consistent with the production line. After discharging each battery cell, recharge it to the cut-off voltage and let it stand for 24 hours. Measure the voltage of each battery cell and obtain the voltage drop curve of each battery cell. According to the voltage drop curve, obtain the stable voltage state of the battery cell of the material system; S2: Divide some of the cells from the production line into two parts, Area A and Area B. Then, group the cells in Area A and Area B by pallet. In step S3, each group of cells in area A is subjected to different formation processes. After the same aging process, each group of cells is divided into different capacities to reach the stable voltage state obtained in step S1. After standing for 4 hours, the voltage OCV1 of each group of cells is measured. After standing for another 24 hours, the voltage OCV2 of each group of cells is measured to obtain the voltage drop of each group of cells. The formation process corresponding to the cell with the least voltage drop is the optimal formation process for the cell with this material system. Each group of cells in Area B is formed using the same formation process. After undergoing different aging processes, each group of cells is divided into different capacities and brought to the stable voltage state obtained in S1. After standing for 4 hours, the voltage OCV3 of each group of cells is measured. After each group of cells is left for one day, the voltage OCV4 of each group of cells is measured. The aging process corresponding to the cell with the least voltage drop is the optimal aging process for the cell with this material system. Voltage drop data can quickly and sensitively characterize the performance of cells with different formation and aging processes, facilitating accurate screening of cell processes.

[0005] As an optional technical solution of the present invention, in step S1, each battery cell is first discharged to 2.5V with a current of 1C on the charging and discharging equipment, and after standing for 5 minutes, it is charged to the cut-off voltage with a current of 0.5C.

[0006] As an optional technical solution of the present invention, in step S1, the dielectric voltage is 3.6V-4.2V.

[0007] Compared with the prior art, the present invention has the following beneficial effects: the present invention characterizes the performance of battery cells under different formation processes and different high-temperature aging conditions through the voltage drop data of the battery cells under the same voltage state after capacity division, and can realize batch testing and characterization on the production line, which is conducive to the accurate screening of the formation process and aging process. It has certain versatility and is highly competitive in the same field. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0009] Figure 1 This is the voltage drop curve of the battery cell after capacity division on the production line; Figure 2 The OCV1 distribution diagrams of three groups of battery cells using different formation processes are shown below. Figure 3 The OCV2 distribution diagrams of three groups of battery cells using different formation processes are shown below. Figure 4 The electrochemical impedance data distribution diagram of three groups of battery cells using different formation processes; Figure 5 The following is the distribution diagram of cycle data of three groups of battery cells using different formation processes; Figure 6 The OCV3 distribution diagram of three groups of battery cells using different aging processes; Figure 7 The OCV4 distribution diagram of three groups of battery cells using different aging processes; Figure 8 The electrochemical impedance data distribution diagram of three groups of battery cells using different aging processes; Figure 9 The following is a distribution diagram of cycle data for three groups of battery cells using different aging processes. DETAILED DESCRIPTION

[0010] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without creative work are within the scope of protection of the present invention. Example

[0011] A method for screening battery cell formation and aging processes, comprising the following steps: S1, take several battery cells with the same material system after capacity division, place them on the charging and discharging equipment for charge and discharge test, the charging and discharging equipment adopts the Abin cabinet charging and discharging equipment, the charging and discharging mode is consistent with the production line, the specific steps are 1C current discharge to 2.5V, stand for 5 minutes, and then charge with 0.5C current to the cut-off voltage, the cut-off voltage is 3.6V-4.2V, stand for 24 hours, and then measure the voltage of each battery cell to obtain the voltage drop curve of each battery cell. According to the voltage drop curve, the stable voltage state of the battery cell of the material system can be obtained.

[0012] S2, take some battery cells from the production line and divide them into two parts, area A and area B. The battery cells in area A and area B are grouped on a pallet basis. The battery cells in area A are used to test and screen out suitable formation processes, and the battery cells in area B are used to test and screen out suitable aging processes.

[0013] S3, each group of battery cells in area A is subjected to different formation processes. After aging through the same aging process, each group of battery cells is divided into different capacities to reach the stable voltage state obtained in step S1. After standing for 4 hours, the voltage OCV1 of each group of battery cells is tested. After standing for 24 hours, the voltage OCV2 of each group of battery cells is tested. Based on the difference between OCV1 and OCV2 of each group of voltages, the voltage drop of each group of battery cells is calculated. By comparing the voltage drops of each group of battery cells, the group of battery cells with the least voltage drop is selected. The formation process corresponding to this group of battery cells is the optimal formation process for the battery cells of this material system. Each group of battery cells in area B is formed using the same formation process, and then aged through different aging processes. After that, each group of battery cells is divided into the stable voltage state obtained in step S1. After standing for 4 hours, the voltage OCV3 of each group of battery cells is tested. Then, after each group of battery cells is placed for 1 day, the voltage OCV4 of each group of battery cells is measured. According to the difference between OCV3 and OCV4 of each group of voltages, the voltage drop of each group of battery cells is calculated, and the group of battery cells with the least voltage drop is selected. The aging process corresponding to this group of battery cells is the optimal aging process for the battery cells of this material system.

[0014] As a specific example, take the battery cells after capacity division on the production line and perform charge and discharge tests on the Abin cabinet charging and discharging equipment. After discharging to 2.5V with a 1C current, let it stand for 5 minutes, and then charge to 3.6V-4.2V with a 0.5C current and let it stand for 24 hours. The voltage of each battery cell is measured and the voltage drop curve of each battery cell is obtained. The voltage drop curve is as follows: Figure 1 As shown, the stable voltage state of the battery cell of this material system is screened out; Then the production line cells were divided into three groups, namely group A1, group A2 and group A3. The three groups of cells used different formation processes. The cells in group A1 used formation process 1, first charged to 3.5V with a current of 0.2C, and then charged to 3.6V with a current of 0.35C. The cells in group A2 used formation process 2, first charged to 3.5V with a current of 0.2C, and then charged to 3.7V with a current of 0.35C. The cells in group A3 used formation process 3, first charged to 3.5V with a current of 0.2C, and then charged to 3.9V with a current of 0.35C. Then, each group of cells was left to stand for 4 hours and the polarization of the cells was eliminated before testing the OCV1 of each cell. The results are as follows: Figure 2 As shown, after one day of storage, OCV2 was tested and the results were as follows Figure 3 As shown by Figure 2 and Figure 3 From the data, we can see that the voltage drop of the battery cells in group A3 is the lowest. Therefore, it can be judged that among groups A1, A2 and A3, the optimal formation process for the battery cells of this material system is the formation process corresponding to the battery cells in group A3.

[0015] The electrochemical impedance and cycle data of the cells in groups A1, A2 and A3 are shown in Figure 2. Figure 4 and Figure 5 As shown by Figure 4 and Figure 5 It can be seen that the data of the A3 group battery cells are the best, that is, among the A1, A2 and A3 group battery cells, the chemical formation process used by the A3 group has the best effect.

[0016] In order to further improve the accuracy of the results, the battery cells can be divided into more groups according to actual conditions, thereby improving the accuracy of various parameters of the formation process.

[0017] As another specific example, the battery cells after capacity separation on the production line are tested on the Abin cabinet charging and discharging equipment. After discharging to 2.5V with a 1C current, they are left to stand for 5 minutes. Then they are charged to 3.6V-4.2V with a 0.5C current and left to stand for 24 hours. The voltage of each battery cell is measured and the voltage drop curve of each battery cell is obtained. The voltage drop curve is as follows: Figure 1 As shown, the stable voltage state of the battery cell of this material system is screened out; Then the production line cells were divided into three groups, namely group B1, group B2 and group B3. The three groups adopted the same formation process and different aging schemes. Among them, the cells of group B1 adopted high temperature aging process 1 and aged at 45℃ for 3 days, the cells of group B2 adopted high temperature aging process 2 and aged at 45℃ for 4 days, and the cells of group B3 adopted high temperature aging process 3 and aged at 45℃ for 5 days. Then, the cells of each group were divided into the same stable voltage state, and each group of cells was left to stand for 4 hours to eliminate cell polarization. Then, the OCV3 of each cell was tested. The results are as follows: Figure 6 As shown, after one day of storage, OCV4 was tested and the results were as follows Figure 7 As shown. Figure 6 and Figure 7 The data shows that the voltage drop of the battery cells is almost the same under different aging processes, which shows that different aging processes have little impact on the battery cells.

[0018] The electrochemical impedance and cycle data of the cells of group B1, group B2 and group B3 are as follows: Figure 8 and Figure 9 As shown by Figure 8 and Figure 9 The results shown are consistent with the voltage drop data of the three groups of battery cells after capacity separation, further proving that the voltage drop data can be used to quickly and sensitively characterize the performance of battery cells under different process conditions, and thus the formation process and aging process can be screened based on the voltage drop data.

[0019] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0020] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for screening battery cell formation and aging processes, characterized by: The following steps are involved: S1: Take several battery cells with the same material system and place them on a charging and discharging device for testing. The charging and discharging mode of the charging and discharging device is consistent with the production line. After discharging each battery cell, recharge it to the cut-off voltage and let it stand for 24 hours. Measure the voltage of each battery cell and obtain the voltage drop curve of each battery cell. According to the voltage drop curve, obtain the stable voltage state of the battery cell of the material system; S2: Divide some of the cells from the production line into two parts, Area A and Area B. Then, group the cells in Area A and Area B by pallet. In step S3, each group of cells in area A is subjected to different formation processes. After the same aging process, each group of cells is divided into different capacities to reach the stable voltage state obtained in step S1. After standing for 4 hours, the voltage OCV1 of each group of cells is measured. After standing for another 24 hours, the voltage OCV2 of each group of cells is measured to obtain the voltage drop of each group of cells. The formation process corresponding to the cell with the least voltage drop is the optimal formation process for the cell with this material system. Each group of battery cells in area B is formed using the same formation process. After different aging processes, each group of battery cells is divided into different capacities to the stable voltage state obtained by S1. After standing for 4 hours, the voltage OCV3 of each group of battery cells is tested. Then, after each group of battery cells is placed for 1 day, the voltage OCV4 of each group of battery cells is measured. The aging process corresponding to the battery cell with the least voltage drop is the optimal aging process for the battery cell of this material system.

2. The method for screening battery cell formation and aging processes according to claim 1, characterized in that: In step S1, each battery cell is first discharged to 2.5V with a current of 1C on the charging and discharging equipment, and then charged to the cut-off voltage with a current of 0.5C after standing for 5 minutes.

3. The method for screening battery cell formation and aging processes according to claim 1, wherein: In step S1, the dielectric voltage is 3.6V-4.2V.

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