Method for determining optimal liquid injection and infiltration conditions of battery cell

Abstract

The invention relates to the technical field of batteries, in particular to a method for determining optimal liquid injection and infiltration conditions of a battery cell. According to the method provided by the invention, by performing isotope labeling on the electrolyte in the battery cell, accurate monitoring on the electrolyte and monitoring on the whole life cycle of the battery are realized, so that the problem of electrolyte insufficiency is found and solved in time, subsequent destructive inspection is avoided, the electrolyte injection amount and infiltration conditions can be optimized, and the service life of the battery is prolonged. The performance and the service life of the battery are effectively improved. And the method can obtain the optimal electrolyte injection and infiltration conditions according to the optimal electrolyte infiltration condition, so that the subsequent long-term cycle performance detection is omitted, and the time cost and the test cost are effectively saved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a method for determining optimal liquid injection and wetting conditions of a battery cell. Background Art

[0002] In the field of battery manufacturing technology, electrolyte management is a key link. The amount of electrolyte injected directly affects the performance and life of the battery. Too little electrolyte will lead to insufficient battery capacity, while too much electrolyte will increase the internal pressure of the battery and increase safety risks. Therefore, it is very important to accurately control the amount of electrolyte injected.

[0003] In the field of electrolyte management technology, the main method currently used is to determine the amount of electrolyte injected through disassembly experiments and experience. Although this method can have a certain effect, since the performance and life of the battery are affected by many factors, such as temperature, humidity, number of charge and discharge times, etc., this method has limited accuracy and cannot monitor the entire life cycle of the battery. It can only ensure the appropriate amount of electrolyte through regular inspection and maintenance, but it often requires destructive inspection of the battery and cannot achieve non-destructive testing. In addition, some researchers have designed the amount of electrolyte injected into the battery cell by measuring the battery's voltage, current, temperature and other parameters, and then calculating the electrolyte consumption through a formula. However, this theoretical calculation method requires a large number of parameters to be known quantities, and the measurement is complex and difficult, the calculation is cumbersome, the error is large, and the injection volume boundary is difficult to control.

[0004] Therefore, there is an urgent need to provide a new method for determining the liquid injection amount of a battery cell. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for determining the optimal injection and wetting conditions of a battery cell.

[0006] In a first aspect, the present invention provides a method for determining optimal injection and wetting conditions of a battery cell, the method comprising the following steps:

[0007] (1) using an isotope-labeled electrolyte, and then sequentially performing a first injection, infiltration, formation, a second injection, and aging on the bare battery cell, wherein the first injection volume, the infiltration time, and the second injection volume are set with multiple sets of variables to obtain multiple groups of battery cells;

[0008] (2) Using radioactive autoradiography technology to monitor the electrolyte infiltration in the central area of ​​the pole piece in the middle layer of the pole core, and then conducting cycle performance tests on the obtained multiple groups of battery cells, and taking the infiltration condition corresponding to the best cycle performance as the best infiltration condition;

[0009] (3) Using isotope-labeled electrolyte, the bare battery cell is then subjected to first injection, infiltration, formation, second injection and aging in sequence, wherein the first injection volume, infiltration time and second injection volume are set with multiple sets of variables to obtain multiple groups of battery cells, and the radioactive autoradiography technology is used to monitor the infiltration of the electrolyte in the central area of ​​the pole piece in the middle layer of the pole core. When the electrolyte infiltration condition meets the optimal infiltration condition described in step (2), the corresponding injection and infiltration conditions are the optimal injection and infiltration conditions of the battery cell.

[0010] As a preferred technical solution of the present invention, the isotopes include 2 H and 14 Any one or both of C.

[0011] As a preferred technical solution of the present invention, the proportion of the isotope-labeled component in the component is 0.01-0.5%.

[0012] As a preferred technical solution of the present invention, the isotope in step (3) is the same as the isotope in step (1).

[0013] As a preferred technical solution of the present invention, the electrolyte infiltration condition is the isotope signal percentage of the central area of ​​the pole piece in the middle layer of the pole core;

[0014] The isotope signal percentage of the central area of ​​the pole piece in the middle layer of the pole core = A / B × 100%;

[0015] Among them, A is the isotope signal intensity of the central area of ​​the pole piece in the middle layer of the electrode core to be tested, and B is the isotope signal intensity of the central area of ​​the pole piece in the middle layer of the electrode core after the same bare battery cell is immersed in the same electrolyte for 120 hours.

[0016] As a preferred technical solution of the present invention, the cycle performance is the number of cycles when the capacity retention rate reaches 90%.

[0017] As a preferred technical solution of the present invention, the total liquid injection amount of the battery cell is the rated capacity of the battery cell×(2-3.5) mg / Ah.

[0018] As a preferred technical solution of the present invention, taking the total liquid injection amount of the battery core as 100%, the first liquid injection amount is 50-100% of the total liquid injection amount of the battery core.

[0019] As a preferred technical solution of the present invention, the infiltration time is 2-60h.

[0020] As a preferred technical solution of the present invention, the formation method in step (3) is the same as the formation method in step (1).

[0021] As a preferred technical solution of the present invention, the aging method in step (3) is the same as the aging method in step (1).

[0022] As a preferred technical solution of the present invention, the battery cell described in step (3) is the same as the battery cell described in step (1). It can be understood that the same battery cell described in the present invention means that the material type, formula, electrode thickness, compaction density, electrode size and battery cell thickness of the positive electrode plate and the negative electrode plate of the battery cell are respectively the same, but the electrolyte formula, battery cell shape and shell type may be different.

[0023] The technical solution provided by the embodiment of the present invention has the following advantages compared with the prior art:

[0024] The method provided by the present invention realizes accurate monitoring of the electrolyte and monitoring of the entire life cycle of the battery by isotope labeling the electrolyte in the battery core, thereby timely discovering and solving the problem of insufficient electrolyte, avoiding subsequent destructive inspections and optimizing the electrolyte injection amount and infiltration conditions, thereby effectively improving the performance and life of the battery. In addition, the method of the present invention can obtain the optimal injection and infiltration conditions based on the optimal infiltration conditions of the electrolyte, eliminating the need for subsequent long-term cycle performance testing, and effectively saving time and testing costs. DETAILED DESCRIPTION

[0025] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0026] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0028] In the field of electrolyte management technology, the main method currently used is to determine the amount of electrolyte injected through disassembly experiments and experience. However, this method cannot achieve precise control of the electrolyte, resulting in the battery's performance and life failing to reach the optimal state, and it is also impossible to monitor the battery's entire life cycle, and it is impossible to promptly discover and solve the problem of insufficient electrolyte. In addition, this method often requires destructive inspection of the battery, and non-destructive testing cannot be achieved. Therefore, an embodiment of the present invention provides a method for determining the optimal injection and wetting conditions of a battery cell.

[0029] First, an embodiment of the present invention provides a method for determining the optimal injection and wetting conditions of a battery cell, comprising the following steps:

[0030] (1) using an isotope-labeled electrolyte, and then sequentially performing a first injection, infiltration, formation, a second injection, and aging on the bare battery cell, wherein the first injection volume, the infiltration time, and the second injection volume are set with multiple sets of variables to obtain multiple groups of battery cells;

[0031] (2) Using radioactive autoradiography technology to monitor the electrolyte infiltration in the central area of ​​the pole piece in the middle layer of the pole core, and then conducting cycle performance tests on the obtained multiple groups of battery cells, and taking the infiltration condition corresponding to the best cycle performance as the best infiltration condition;

[0032] (3) Using isotope-labeled electrolyte, the bare battery cell is then subjected to first injection, infiltration, formation, second injection and aging in sequence, wherein the first injection volume, infiltration time and second injection volume are set with multiple sets of variables to obtain multiple groups of battery cells, and the radioactive autoradiography technology is used to monitor the infiltration of the electrolyte in the central area of ​​the pole piece in the middle layer of the pole core. When the electrolyte infiltration condition meets the optimal infiltration condition described in step (2), the corresponding injection and infiltration conditions are the optimal injection and infiltration conditions of the battery cell.

[0033] Among them, the optimal cycle performance is: when multiple groups of battery cells reach the same capacity retention rate, the cycle performance corresponding to the battery cell with the highest number of cycles is the optimal cycle performance, or, when the number of cycles of multiple groups of battery cells is the same, the cycle performance corresponding to the battery cell with the highest capacity retention rate is the optimal cycle performance.

[0034] The method provided in the embodiment of the present invention realizes accurate monitoring of the electrolyte and monitoring of the entire life cycle of the battery by isotope labeling of the electrolyte in the battery cell, thereby timely discovering and solving the problem of insufficient electrolyte, avoiding subsequent destructive inspections and optimizing the electrolyte injection volume and infiltration conditions, thereby effectively improving the performance and life of the battery. In addition, the method of the present invention can obtain the optimal injection and infiltration conditions based on the optimal infiltration conditions of the electrolyte, eliminating the need for subsequent long-term cycle performance testing, and effectively saving time and testing costs. Specifically:

[0035] The method provided by the embodiment of the present invention is to carry out isotope labeling of the electrolyte in the battery cell and to carry out isotope monitoring by radioactive autoradiography technology, so as to achieve precise control of the electrolyte, monitor the consumption of the electrolyte in the formation, aging, constant volume and circulation process, and timely discover and solve the problem of insufficient electrolyte. On this basis, according to the strength of the isotope monitoring signal and the cycle performance test results, the optimal infiltration of the electrolyte in the battery cell is obtained, and then the optimal injection and infiltration conditions of the battery cells of different systems and different life cycles are corrected according to the optimal infiltration conditions, avoiding the problem of poor battery performance and life due to too much or too little electrolyte, thereby improving the performance and life of the battery. In addition, by monitoring the content changes of isotopes in each process through radioactive autoradiography technology, the monitoring of the full life cycle of the battery is achieved, and the battery does not need to be destructively inspected, so that non-destructive testing is achieved. Moreover, the method can obtain the optimal injection and infiltration conditions according to the optimal infiltration of the electrolyte, eliminating the need for subsequent long-term cycle performance testing, and predicting the performance of the battery cell in advance in the long-term cycle, effectively saving time and testing costs.

[0036] Radioactive autoradiography is a development technology that detects the internal distribution of radioactive nuclides or their labeled compounds based on the principle of radioactive nuclide tracing and the property of radiation making photosensitive materials sensitive to light. Radioactive autoradiography expresses the distribution of markers in the form of images, and has the characteristics of accurate positioning, high sensitivity and non-invasiveness. It is widely used in the fields of medicine, environmental protection and national defense. The embodiment of the present invention uses radioactive autoradiography technology to monitor the electrolyte infiltration in the central area of ​​the pole piece in the middle layer of the pole core, which can achieve: 1. Accurate control of the electrolyte to avoid the problem of poor battery performance and life due to excessive or insufficient electrolyte; 2. Monitoring the consumption of electrolyte: By monitoring the consumption of electrolyte in the formation, aging, constant volume and circulation process, the use of electrolyte can be monitored, and the problem of insufficient electrolyte can be discovered and solved in time, thereby improving the service life of the battery; 3. Monitoring the entire life cycle of the battery can be achieved, and there is no need to perform destructive inspections on the battery later, thus achieving non-destructive testing and effectively improving the safety and reliability of the battery; 4. According to the correlation between the cycle performance and the infiltration condition, the optimal injection and infiltration conditions are obtained, and the cycle diving caused by the lean liquid is avoided in advance, thereby improving the cycle life of the battery. Through the above improvements, the performance and life of the battery are effectively improved, so that the battery can work in the best state.

[0037] It can be understood that the central area of ​​the pole piece in the middle layer of the pole core refers to the middle positive and negative electrode layers of the total number of layers of the battery cell, and is the center position of the surface of the positive and negative electrode layers.

[0038] In some embodiments of the invention, the isotopes include 2 H and 14 Any one or both of C.

[0039] In some embodiments of the present invention, the isotope-labeled component accounts for 0.01-0.5% of the component, for example, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc. However, the present invention is not limited to the listed values, and other values ​​not listed in the range are also applicable. When the content of the isotope label is within this range, the infiltration of the electrolyte can be accurately and effectively monitored.

[0040] In some embodiments of the present invention, the isotope in step (3) is the same as the isotope in step (1).

[0041] The implementation manner of the present invention obtains the optimal electrolyte infiltration condition after the formation, aging and cycle performance tests of multiple groups of battery cells are carried out in the early stage. When the injection amount of the battery cells of the same system is judged later, it is only necessary to use the same isotope to carry out the formation and aging tests of multiple groups of battery cells. When the electrolyte infiltration condition meets the optimal infiltration condition, the optimal injection and infiltration conditions of the battery cells are obtained.

[0042] In some embodiments of the present invention, the electrolyte infiltration condition is the isotope signal percentage in the central area of ​​the pole piece in the middle layer of the pole core;

[0043] The isotope signal percentage of the central area of ​​the pole piece in the middle layer of the pole core = A / B × 100%;

[0044] Among them, A is the isotope signal intensity of the central area of ​​the middle layer of the pole piece of the pole core to be tested, and B is the isotope signal intensity of the central area of ​​the middle layer of the pole piece of the same bare cell after being immersed in the same electrolyte for 120 hours. It can be understood that the same bare cell refers to a bare cell that is the same as the cell to be tested and has not undergone the first injection, infiltration, formation, second injection and aging steps, and the same electrolyte refers to an electrolyte with the same composition, the same dosage and the same isotope labeling amount as the electrolyte in step (1). When the isotope signal intensity of the pole piece to be tested is consistent with that of the pole piece immersed for 120 hours, the whole cell is fully infiltrated.

[0045] In some embodiments of the present invention, the infiltration conditions of the electrolyte are divided into 5 levels, where:

[0046] Level 1: The central area of ​​the pole piece in the middle layer of the pole core, the isotope signal is less than 70%;

[0047] Second level: the central area of ​​the pole piece in the middle layer of the pole core, 70%≤isotope signal<80%;

[0048] Level 3: The central area of ​​the pole piece in the middle layer of the pole core, 80%≤isotope signal<90%;

[0049] Level 4: The central area of ​​the pole piece in the middle layer of the pole core, 90%≤isotope signal<95%;

[0050] Level 5: In the central area of ​​the pole piece in the middle layer of the pole core, the isotope signal is 95% ≤ ≤ 100%.

[0051] In some embodiments of the present invention, the cycle performance is the number of cycles when the capacity retention rate reaches 90%. The higher the number of cycles, the better the cycle performance of the battery. The optimal cycle performance, that is, the wetting level corresponding to the highest number of cycles, is the optimal wetting condition. In other words, when the wetting condition of the electrolyte is the optimal wetting condition, the battery performance is optimal.

[0052] In some embodiments of the present invention, the total injection amount of the battery cell is the rated capacity of the battery cell × (2-3.5) mg / Ah, for example, it can be rated capacity × 2 mg / Ah, rated capacity × 2.5 mg / Ah, rated capacity × 3 mg / Ah, rated capacity × 3.5 mg / Ah, etc., but the present invention is not limited to the listed values, and other values ​​not listed in the range are also applicable. When the total injection amount of the battery cell is within the above range, the optimal injection and wetting conditions of the battery cell can be obtained more quickly.

[0053] In some embodiments of the present invention, the first injection amount is 50-100% of the total injection amount of the battery cell, for example, it can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, etc., based on the total injection amount of the battery cell as 100%. However, the present invention is not limited to the listed values, and other values ​​not listed in the range are also applicable. When the first injection amount is within the above range, the optimal injection and wetting conditions of the battery cell can be obtained more quickly.

[0054] In some embodiments of the present invention, the soaking time is 2-60 hours, for example, 2 hours, 10 hours, 20 hours, 30 hours, 36 hours, 42 hours, 48 ​​hours, 55 hours, 60 hours, etc. However, the present invention is not limited to the listed values, and other values ​​not listed in the range are also applicable. The above soaking time comprehensively considers the production efficiency and production line cost, and can shorten the soaking time as much as possible and reduce the cost while meeting the performance of the battery cell.

[0055] In some embodiments of the present invention, the method of formation in step (3) is the same as the method of formation in step (1). The method of formation is not particularly limited in the embodiments of the present invention, and is a commonly used formation method in the art, and the same formation conditions need only be used in step (1) and step (3).

[0056] In some embodiments of the present invention, the aging method in step (3) is the same as the aging method in step (1). The aging method in the embodiments of the present invention is not particularly limited, and is a commonly used aging method in the art, and only the same formation conditions need to be used in step (1) and step (3).

[0057] In some embodiments of the present invention, the battery cell in step (3) is the same as the battery cell in step (1). It is understood that the battery cells described in the embodiments of the present invention are the same in that the material type, formula, thickness, compaction density, size and thickness of the positive and negative electrode sheets of the battery cells are the same, but the electrolyte formula, battery cell shape and shell type may be different.

[0058] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention will be further described in detail in conjunction with the embodiments below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its applications. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0059] If no specific techniques or conditions are specified in the examples, the conventional techniques or conditions in the art, or the techniques or conditions described in the literature, or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0060] Example 1

[0061] This embodiment provides a method for determining optimal injection and wetting conditions of a battery cell, comprising the following steps:

[0062] (1) A lithium-ion battery with a capacity of 50 Ah was selected, the positive electrode was NCM622, the negative electrode was Gr, the separator was double-sided glue-coated ceramic (base film 9 μm + glue layer 3 μm + ceramic layer 2 μm), the electrolyte composition was EC:EMC:DEC=1:1:1, 1 mol / L LiPF6, and the electrolyte solvent was 2 H isotope (deuterium can be used for long-term tracer experiments due to its stability) labeling, the deuterium content in the solvent is 0.1% of hydrogen; then the bare battery cell is sequentially subjected to the first injection, infiltration, formation, second injection and aging, wherein the formation method is to use a constant current of 0.2C to 3.75V, and the aging method is to place at 45°C for 48h, and the first injection volume, infiltration time and second injection volume are respectively set with multiple groups of variables (each group is set with at least 2 variables to facilitate the deuterium signal detection in step (2)), as shown in Table 1, to obtain multiple groups of battery cells;

[0063] (2) Using radioactive autoradiography technology to monitor the electrolyte infiltration in the central area of ​​the pole piece in the middle layer of the pole core, the isotope signal percentage in the central area of ​​the pole piece in the middle layer of the pole core is obtained = A / B × 100%;

[0064] Wherein, A is the isotope signal intensity of the central area of ​​the pole piece in the middle layer of the electrode core to be tested, and B is the isotope signal intensity of the central area of ​​the pole piece in the middle layer of the electrode core of the same bare battery cell after being immersed in the same electrolyte as step (1) for 120 hours.

[0065] The electrolyte infiltration conditions are divided into 5 levels, including:

[0066] Level 1: The central area of ​​the pole piece in the middle layer of the pole core, the isotope signal is less than 70%;

[0067] Second level: the central area of ​​the pole piece in the middle layer of the pole core, 70%≤isotope signal<80%;

[0068] Level 3: The central area of ​​the pole piece in the middle layer of the pole core, 80%≤isotope signal<90%;

[0069] Level 4: The central area of ​​the pole piece in the middle layer of the pole core, 90%≤isotope signal<95%;

[0070] Level 5: The central area of ​​the pole piece in the middle layer of the pole core, 95%≤isotope signal≤100%; the results are shown in Table 1.

[0071] Then, the obtained multiple groups of battery cells were subjected to cycle performance tests (voltage range was 2.5V to 4.4V, current range was 1.0C to 2.0C), and the number of cycles when the capacity retention rate was 90% was obtained. The results are shown in Table 1.

[0072] It should be noted that the above-mentioned test lithium-ion battery is only an example listed for determining the optimal injection and wetting conditions of the battery cell. The present invention is not limited to this type of battery. The raw materials, proportions, parameters and processes can be replaced by other conventional raw materials, proportions, parameters and processes in the art to form a battery different from the test lithium-ion battery.

[0073] The test conditions and results are shown in Table 1:

[0074] Table 1

[0075]

[0076] It can be found from Table 1 that the cycle performance of groups 1-10 is the best, and the corresponding wetting condition is level five, that is, the electrolyte wetting level is level five as the optimal wetting condition.

[0077] (3) The electrolyte solvent is 2H isotope labeling, the deuterium content in the solvent is 0.1% of hydrogen, and then the same system bare battery cells that are different from the batch in step (1) are sequentially subjected to the first injection, infiltration, formation, second injection and aging, wherein the composition of the electrolyte, the formation and aging methods are the same as those in step (1), the first injection volume, the infiltration time and the second injection volume are shown in Table 2, and the battery cells are obtained. The radioactive autoradiography technology is used to monitor the infiltration of the electrolyte in the central area of ​​the pole piece in the middle layer of the pole core, as shown in Table 2:

[0078] Table 2

[0079]

[0080] It can be found that the wetting conditions of groups 1-11 are level five, and the corresponding injection and wetting conditions are the optimal injection and wetting conditions for the battery cell: the first injection volume is 106 g, the immersion time is 36 h, and the second injection volume is 19 g.

[0081] Example 2

[0082] This example is used to verify the feasibility of the method of the present invention.

[0083] The two groups of cells obtained in step (3) of Example 1 were subjected to a cycle performance test (voltage range of 2.5 V to 4.4 V, current range of 1.0 C to 2.0 C), and the number of cycles when the capacity retention rate was 90% was obtained. The results are shown in Table 3:

[0084] Table 3

[0085] Group Number of cycles 1-11 771 1-12 694

[0086] It can be found that the cycle performance of group 1-11 is the best, indicating that the method of the present invention is feasible.

[0087] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0088] The above description is only a specific embodiment of the present invention, so that those skilled in the art can understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments described herein, but should conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for determining the optimal injection and wetting conditions of a battery cell, characterized in that: The method comprises the following steps: (1) using an isotope-labeled electrolyte, and then sequentially performing a first injection, infiltration, formation, a second injection, and aging on the bare battery cell, wherein the first injection volume, the infiltration time, and the second injection volume are set with multiple sets of variables to obtain multiple groups of battery cells; (2) Using radioactive autoradiography technology to monitor the electrolyte infiltration in the central area of ​​the pole piece in the middle layer of the pole core, and then conducting cycle performance tests on the obtained multiple groups of battery cells, and taking the infiltration condition corresponding to the best cycle performance as the best infiltration condition; (3) Using isotope-labeled electrolyte, the bare battery cell is then subjected to first injection, infiltration, formation, second injection and aging in sequence, wherein the first injection volume, infiltration time and second injection volume are set with multiple sets of variables to obtain multiple groups of battery cells, and the radioactive autoradiography technology is used to monitor the infiltration of the electrolyte in the central area of ​​the pole piece in the middle layer of the pole core. When the electrolyte infiltration condition meets the optimal infiltration condition described in step (2), the corresponding injection and infiltration conditions are the optimal injection and infiltration conditions of the battery cell.

2. The method according to claim 1, characterized in that: The isotopes include 2 H and 4 Any one or both of C.

3. The method according to claim 1 or 2, characterized in that: The isotope-labeled component accounts for 0.01-0.5% of the component.

4. The method according to claim 1 or 2, characterized in that: The isotope in step (3) is the same as the isotope in step (1).

5. The method according to claim 1 or 2, characterized in that: The electrolyte infiltration condition is the isotope signal percentage in the central area of ​​the pole piece in the middle layer of the pole core; The isotope signal percentage of the central area of ​​the pole piece in the middle layer of the pole core = A / B × 100%; Among them, A is the isotope signal intensity of the central area of ​​the pole piece in the middle layer of the electrode core to be tested, and B is the isotope signal intensity of the central area of ​​the pole piece in the middle layer of the electrode core after the same bare battery cell is immersed in the same electrolyte for 120 hours.

6. The method according to claim 1 or 2, characterized in that: The cycle performance is the number of cycles when the capacity retention rate reaches 90%.

7. The method according to claim 1 or 2, characterized in that: The total liquid injection volume of the battery cell is the rated capacity of the battery cell × (2-3.5) mg / Ah.

8. The method according to claim 1 or 2, characterized in that: Taking the total liquid injection amount of the battery core as 100%, the first liquid injection amount is 50-100% of the total liquid injection amount of the battery core.

9. The method according to claim 1 or 2, characterized in that: The infiltration time is 2-60h.

10. The method according to claim 1 or 2, characterized in that: The method of forming in step (3) is the same as the method of forming in step (1); The aging method in step (3) is the same as the aging method in step (1).

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