A method for testing the degree of electrolyte infiltration of a battery cell

Abstract

The invention discloses a method for testing the degree of electrolyte infiltration of a battery cell, comprising: disassembling the battery cell, taking out the positive electrode sheet in the battery cell; preparing a color developing reagent, the color developing reagent comprising chrome black T and an organic binder, the mass ratio of chrome black T to the organic binder in the color developing reagent being 1:4 to 1:9; unfolding the positive electrode sheet; applying the color developing reagent to the positive electrode sheet to form a coating, the coating being located in the central area of ​​the positive electrode sheet; judging whether the coating is wine red, if so, the electrolyte completely infiltrates the battery cell, if not, the electrolyte does not completely infiltrate the battery cell. The method for testing the degree of electrolyte infiltration of a battery cell disclosed in the invention can test the degree of infiltration of the battery cell at a low cost, is simple to operate, has a fast test speed, shortens the production turnover cycle of the battery cell, improves the accuracy of the test, is intuitive and effective, and does not require additional special equipment.

Description

Technical Field

[0001] The invention belongs to the field of battery core infiltration and relates to a method for testing the degree of electrolyte infiltration of a battery core. Background Art

[0002] After the electrolyte is injected into the battery cell, the electrode sheet needs to be completely soaked before the next step can be carried out. The existing methods for judging whether the battery cell is soaked generally include: disassembly direct observation method, volume fractionation and observation method, ultrasonic transmission imaging method, etc.

[0003] The direct observation method is generally performed by disassembling the battery after long-term high-temperature storage, and directly observing the degree of wetting at the positive and negative electrode interfaces with the naked eye. This method has a large error, and the long-term high-temperature storage waiting time is long, which prolongs the battery cell production turnover cycle.

[0004] The direct observation method after the cell is divided into different capacities is to disassemble the cell and observe whether lithium deposition and black spots appear on the interface. This method is time-consuming and the results are not accurate enough.

[0005] Ultrasonic transmission imaging is based on the fact that ultrasound waves are affected by the physical properties of the battery's internal materials during propagation. When the battery is infiltrated with electrolyte, the ultrasonic wave's transmittance will be relatively high; on the contrary, if the electrolyte is poorly infiltrated, the ultrasonic wave's transmittance will decrease. However, ultrasonic transmission imaging is expensive, which increases the production cost of battery cells.

[0006] For example, patent document CN220854546U discloses a battery cell wetting effect detection device, which detects the internal reflection of the battery cell through ultrasonic wave to determine whether there is poor wetting. However, the ultrasonic collector used is expensive and complicated to operate, which increases the production cost of the battery cell.

[0007] The existing technology of judging the degree of telecommunication infiltration by ultrasonic transmission imaging is relatively complicated. The problem of how to judge the degree of electrolyte infiltration of battery cells in a low-cost manner, simple operation, shorten the production turnover cycle of battery cells, and improve the accuracy of testing has not been effectively solved. Summary of the invention

[0008] The purpose of the present invention is to solve the problem of how to determine the electrolyte infiltration degree of a battery cell in a low-cost manner.

[0009] In a first aspect, the present invention provides a method for testing the degree of electrolyte infiltration of a battery cell, comprising:

[0010] Disassemble the battery cell and take out the positive electrode plate in the battery cell;

[0011] preparing a color developing reagent, wherein the color developing reagent comprises chrome black T and an organic binder, wherein the mass ratio of chrome black T to the organic binder in the color developing reagent is 1:4 to 1:9;

[0012] Unfold the positive electrode;

[0013] Applying a color developing reagent to the positive electrode plate to form a coating portion, wherein the coating portion is located in the central area of ​​the positive electrode plate;

[0014] Determine whether the coated area is wine red. If so, the electrolyte completely penetrates the battery cell. If not, the electrolyte does not completely penetrate the battery cell.

[0015] By adopting the above technical solution, the degree of wetting of the battery cell can be tested at low cost, the operation is simple, the test speed is fast, the production turnover cycle of the battery cell is shortened, the accuracy of the test is improved, and it is intuitive and effective without the need for additional special equipment.

[0016] According to another specific embodiment of the present invention, the coating portion includes two coating regions, the coating regions are equal in length and are spaced apart along the length direction of the positive electrode sheet.

[0017] According to another specific embodiment of the present invention, the coating amount of the color developing reagent in each coating area is 6 to 15 mg.

[0018] According to another specific embodiment of the present invention, the coating area includes four coating regions, the coating regions are equal in length, and are spaced apart along the length direction of the positive electrode sheet, and the intervals between two adjacent coating regions are equal.

[0019] According to another specific embodiment of the present invention, the coating amount of the color developing reagent in each coating area is 2 to 4 mg.

[0020] According to another specific embodiment of the present invention, the coating portion includes a coating area, and the coating area is arranged along the length direction of the positive electrode sheet.

[0021] According to another specific embodiment of the present invention, the coating amount of the color developing reagent in the coating area is 10 to 60 mg.

[0022] According to another specific embodiment of the present invention, the color developing reagent further comprises:

[0023] N-methylpyrrolidone, the mass ratio of the organic binder to N-methylpyrrolidone is 3:125-1:100.

[0024] According to another specific embodiment of the present invention, it also includes:

[0025] Determine whether each coated area is wine red. If so, the electrolyte evenly infiltrates the battery cell. If not, the electrolyte infiltrates the battery cell unevenly.

[0026] In a second aspect, the present invention provides a method for screening battery cells, using the above-mentioned method for testing the degree of electrolyte infiltration of battery cells to test the degree of electrolyte infiltration of battery cells to obtain test results, and screening battery cells with complete infiltration according to the test results.

[0027] By adopting the above technical solution, it is possible to screen out battery cells with complete infiltration degree. The operation is simple, the test speed is fast, the production turnover cycle of the battery cells is shortened, the accuracy of the test is improved, it is intuitive and effective, and no additional special equipment is required. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The process of testing the electrolyte wetting degree of the battery cell in the embodiment of the present invention is shown as follows Figure 1 ;

[0029] Figure 2 Schematic diagram of electrode plate coating in an embodiment of the present invention Figure 1 ;

[0030] Figure 3 A schematic diagram showing a rolled-up state of an electrode sheet in an embodiment of the present invention;

[0031] Figure 4 Schematic diagram of electrode plate coating in an embodiment of the present invention Figure 2 ;

[0032] Figure 5 Schematic diagram of electrode plate coating in an embodiment of the present invention Figure 3 ;

[0033] Figure 6 The test method flow of the battery cell electrolyte infiltration degree in the embodiment of the present invention is as follows Figure 2 .

[0034] Explanation of symbols

[0035] 01 positive electrode plate, 02 coating area, 03 coating area, 031 first coating area, 032 second coating area, 033 third coating area, 034 fourth coating area, 035 fifth coating area, 036 sixth coating area. DETAILED DESCRIPTION

[0036] The following specific embodiments illustrate the implementation of the present invention, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Although the description of the present invention will be introduced in conjunction with the preferred embodiment, this does not mean that the features of this invention are limited to this implementation. On the contrary, the purpose of introducing the invention in conjunction with the implementation is to cover other options or modifications that may extend based on the claims of the present invention. In order to provide a deep understanding of the present invention, the following description will include many specific details. The present invention can also be implemented without using these details. In addition, in order to avoid confusion or blurring the focus of the present invention, some specific details will be omitted in the description. 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.

[0037] It should be noted that in this specification, similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0039] The battery cell includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. In a dry state, Chrome Black T appears black.

[0040] When the battery cell is in the process of infiltration, trace amounts of hydrofluoric acid in the electrolyte will dissolve the transition metal on the positive electrode plate, and when the dissolved metal ions encounter chrome black T, a coordination reaction will occur. Under different levels of metal ions and hydrofluoric acid, the developer chrome black T has different color development degrees. When the pH value is less than 6.3, the chrome black T solution appears wine red. When the pH value is between 6.3 and 11.6, the chrome black T solution appears blue. Chrome black T, which has not undergone a chemical reaction, appears black in itself and only changes color when a reaction occurs. The inventor thought of using the color development characteristics of chrome black T and the positive electrode plate material to apply chrome black T to the center area of ​​the battery cell that is most difficult to infiltrate, observe whether chrome black T appears wine red, and judge the degree of infiltration of the battery cell electrode plate, so as to reduce the waiting time for infiltration and avoid inaccuracies caused by direct observation after disassembly. Chrome Black T is particularly suitable for testing the degree of electrolyte infiltration in the battery cell field because of its fast and clear color development and the ability to develop the color of the electrolyte that wets the positive electrode without the need for additional equipment.

[0041] Based on the above principles, reference Figure 1 In a first aspect, the present invention provides a method for testing the degree of electrolyte infiltration of a battery cell, comprising:

[0042] S1: Disassemble the battery cell and take out the positive electrode plate in the battery cell;

[0043] S2: preparing a color developing reagent, the color developing reagent comprising chrome black T and an organic binder, wherein the mass ratio of chrome black T to the organic binder in the color developing reagent is 1:4 to 1:9. Preferably, the organic binder is polyvinylidene fluoride.

[0044] S3: unfold the positive electrode sheet;

[0045] S4: coating a color developing reagent onto the positive electrode plate to form a coating portion, wherein the coating portion is located in a central area of ​​the positive electrode plate;

[0046] S5: Determine whether the coated area is wine red. If so, S5-1: the electrolyte completely infiltrates the battery cell. If not, S5-2: the electrolyte does not completely infiltrate the battery cell.

[0047] By adopting the above technical scheme, the degree of wetting of the battery cell can be tested at low cost, the operation is simple, the test speed is fast, the production turnover cycle of the battery cell is shortened, the accuracy of the test is improved, it is intuitive and effective, and no additional special equipment is required. By judging whether the coating is colored, the accuracy is higher than directly observing the infiltration of the electrode sheet with the naked eye, and it is more intuitive and effective. The battery cell to be tested is extracted from the same batch of battery cells produced and injected to carry out the test of the degree of infiltration of the battery cell electrolyte of the present invention, and the degree of infiltration is tested 6-12 hours after the battery cell is injected with the electrolyte. If the electrolyte of the battery cell to be tested completely infiltrates the electrode sheet, the battery cell produced and injected in the same batch can be carried out to the next process. Compared with the traditional battery cell injection, it waits 48 hours for the infiltration to be complete before carrying out the subsequent process, which shortens the production turnover cycle of the battery cell. Compared with the ultrasonic transmission imaging method, no additional special equipment is required, which reduces the expensive equipment cost of the ultrasonic transmission imaging method, is easy to operate, and reduces the difficulty of operation.

[0048] Specifically, if Figure 2 As shown, the coating part 02 is located at the positive electrode sheet 01 in the center area of ​​the winding core, that is, the coating part 02 is located at the center area of ​​the length direction of the positive electrode sheet 01 after it is unfolded, and the coating part 02 is located at the center area of ​​the width direction of the positive electrode sheet 01 after it is unfolded. The length of the coating part 02 is 1 / 8-1 / 4 of the circumference of the positive electrode sheet 01 (i.e. the winding core), and the width of the coating part is 2%-8% of the width of the positive electrode sheet. The width of the coating part 02 is 1.8mm-7.0mm. This setting can save the amount of color developing reagent and accurately reflect the degree of wetting of the electrode sheet. Reference Figure 2 and Figure 3The present invention is applicable to judging the electrolyte infiltration of cylindrical battery cells. The electrode sheet is rolled along the length direction of the electrode sheet, and the electrolyte is injected after rolling. Because the central hole area A of the winding core and the outer peripheral wall B of the winding core are in contact with the electrolyte, the infiltration effect is better, that is, the C end and the D end of the positive electrode sheet after unfolding are the easiest to infiltrate at the same time, and the coating 02 located in the central area of ​​the positive electrode sheet 01 is the most difficult to infiltrate. If the most difficult to infiltrate central area, that is, the coating 02, is completely infiltrated, it means that the positive electrode sheet 01 of the battery cell is completely infiltrated by the electrolyte.

[0049] Among them, the color developing reagent includes chrome black T and an organic binder, and the mass ratio of chrome black T to the organic binder in the color developing reagent is 1:4 to 1:9. Chrome black T plays an indicating role in the electrolyte on the positive electrode plate. Preferably, the organic binder is polyvinylidene fluoride, and polyvinylidene fluoride (PVDF) acts as a binder to bond chrome black T to the coating 02 of the positive electrode plate 01. The mass ratio of chrome black T and polyvinylidene fluoride is 1:4 to 1:9. In this mass ratio range, it has a coloring effect and is suitable for judging the wetting condition of the positive electrode plate 01.

[0050] According to another specific embodiment of the present invention, Figure 2 and Figure 4 As shown, the coating area 02 includes two coating areas 03, the lengths of the two coating areas 03 are equal, and they are spaced apart along the length direction of the positive electrode sheet 01. Specifically, each coating area 03 has an equal length along the length direction of the positive electrode sheet 01, and is arranged along the length direction of the positive electrode sheet 01, and is sequentially a first coating area 031 and a second coating area 032. The length of the first coating area 031 is 30%-50% of the coating area 02, and the length of the second coating area 032 is 30%-50% of the coating area 02. Preferably, each coating area 03 has an equal area so as to observe the color change after reacting with the color developing reagent. By adopting the above technical solution, it is possible to accurately judge whether the positive electrode sheet 01 of the battery cell is completely infiltrated by the electrolyte.

[0051] According to another specific embodiment of the present invention, continue to refer to Figure 4 , the coating amount of the color developing reagent in each coating area 03 is 6 to 15 mg. That is, the coating amount of the color developing reagent in the first coating area 031 is 10 to 15 mg, the coating amount of the color developing reagent in the second coating area 032 is 6 to 15 mg, and the total coating amount of the coating area 02 is 12 to 40 mg. By adopting the above technical solution, it is possible to accurately determine whether the positive electrode sheet 01 of the battery cell is completely infiltrated by the electrolyte, and save the amount of the color developing reagent.

[0052] According to another specific embodiment of the present invention, Figure 2 and Figure 5The coating 02 includes four coating regions 03 , which are of equal length and are arranged at intervals along the length direction of the positive electrode sheet 01 , and the intervals between two adjacent coating regions 03 are equal. That is, the coating areas 03 are arranged equidistantly along the length direction of the positive electrode plate 01, namely the third coating area 033, the fourth coating area 034, the fifth coating area 035, and the sixth coating area 036. The length of the third coating area 033 is 6%-25% of the coating location 02, the length of the fourth coating area 034 is 6%-25% of the coating location 02, the length of the fifth coating area 035 is 6%-25% of the coating location 02, and the length of the sixth coating area 036 is 6%-25% of the coating location 02. Preferably, the length of the third coating area 033 is 6.25%-12.5% ​​of the coating location 02, the length of the fourth coating area 034 is 6.25%-12.5% ​​of the coating location 02, the length of the fifth coating area 035 is 6.25%-12.5% ​​of the coating location 02, and the length of the sixth coating area 036 is 6.25%-12.5% ​​of the coating location 02. By adopting the above technical solution, it is possible to accurately determine whether the positive electrode plate 01 of the battery cell is infiltrated by the electrolyte.

[0053] According to another specific embodiment of the present invention, continue to refer to Figure 5 , the coating amount of the color developing reagent in each coating area 03 is 2 to 4 mg. That is, the coating amount of the color developing reagent in the third coating area 033 is 2 to 4 mg, the coating amount of the color developing reagent in the fourth coating area 034 is 2 to 4 mg, the coating amount of the color developing reagent in the fifth coating area 035 is 2 to 4 mg, and the coating amount of the color developing reagent in the sixth coating area 036 is 2 to 4 mg. By adopting the above technical solution, the degree of wetting of the positive electrode sheet 01 of the battery cell can be accurately determined, and the amount of the color developing reagent can be saved.

[0054] According to another specific embodiment of the present invention, continue to refer to Figure 2 The coating part 02 includes a coating area 03, and the coating area 03 is arranged along the length direction of the positive electrode sheet 01. The above technical solution is simple to operate and can accurately determine the electrolyte infiltration degree of the positive electrode sheet 01 of the battery cell.

[0055] According to another specific embodiment of the present invention, the coating amount of the color developing reagent in the coating area 03 is 10 to 60 mg. By adopting the above technical solution, the electrolyte infiltration condition of the positive electrode plate of the battery cell can be accurately determined.

[0056] According to another specific embodiment of the present invention, the color developing reagent further comprises:

[0057] N-methylpyrrolidone, the mass ratio of the organic binder to N-methylpyrrolidone is 3:125-1:100. Preferably,

[0058] The organic binder is polyvinylidene fluoride.

[0059] Wherein, N-methylpyrrolidone is referred to as NMP, that is, the mass ratio of polyvinylidene fluoride (PVDF) to N-methylpyrrolidone (NMP) is 1.0%-2.4%, that is, the solid content of polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) is 1.0%-2.4%. Preferably, the mass ratio of polyvinylidene fluoride to N-methylpyrrolidone is 2:100, that is, the mass ratio of polyvinylidene fluoride (PVDF) to N-methylpyrrolidone (NMP) is 2%, and the solid content of polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) is 2%.

[0060] According to another specific embodiment of the present invention, referring to Figure 6 , the test methods for the degree of electrolyte infiltration of the battery cell also include:

[0061] S6: Determine whether each coated area is wine red. If so, S6-1: The electrolyte evenly infiltrates the battery cell. If not, S6-2: The electrolyte infiltrates the battery cell unevenly.

[0062] Continue to refer Figure 4 If both the first coating area 031 and the second coating area 032 are wine red, it means that both the first coating area 031 and the second coating area 032 are infiltrated and the battery cell is infiltrated evenly. If the first coating area 031 or the second coating area 032 is not wine red, but the black color of the chrome black T is shown, it means that the infiltration is uneven. Figure 5 , the third coating area 033, the fourth coating area 034, the fifth coating area 035, and the sixth coating area 036 are all infiltrated, and the battery cell is infiltrated evenly. If any coating area 03 among the third coating area 033, the fourth coating area 034, the fifth coating area 035, and the sixth coating area 036 does not show wine red, but shows the black color of the chrome black T itself, it means that the infiltration is uneven. The above technical solution can accurately determine whether the electrolyte infiltration of the positive electrode sheet 01 of the battery cell is uniform. Reference Figure 2 If the coating area 03 of the coating 02 is uniformly burgundy, it means that the electrolyte infiltration of the positive electrode plate 01 of the battery cell is uniform. If the coating area 03 is unevenly burgundy, it means that the electrolyte infiltration of the positive electrode plate 01 of the battery cell is uneven.

[0063] Next, specific embodiments of the present invention are introduced.

[0064] Example 1: Disassemble the battery cell and take out the positive electrode sheet in the battery cell; prepare a color developing reagent, the color developing reagent includes chrome black T and polyvinylidene fluoride, and the mass ratio of chrome black T to polyvinylidene fluoride in the color developing reagent is 1:4; unfold the positive electrode sheet; apply the color developing reagent to the positive electrode sheet to form a coating area, which is located in the central area of ​​the positive electrode sheet. Apply the coating area at the coating area, there is 1 coating area, the area of ​​the coating area is 36mm*4mm, and the spraying amount of the coating area is 12mg.

[0065] Example 2: Disassemble the battery cell and take out the positive electrode plate in the battery cell; prepare a color developing reagent, the color developing reagent includes chrome black T and polyvinylidene fluoride, and the mass ratio of chrome black T to polyvinylidene fluoride in the color developing reagent is 1:5; unfold the positive electrode plate; apply the color developing reagent to the positive electrode plate to form a coating, and the coating is located in the central area of ​​the positive electrode plate. The coating is performed in the coating area of ​​the coating, there is 1 coating area, the area of ​​the coating area is 36mm*4mm, and the spraying amount of the coating area is 12mg. Example 3: Disassemble the battery cell and take out the positive electrode plate in the battery cell; prepare a color developing reagent, the color developing reagent includes chrome black T and polyvinylidene fluoride, and the mass ratio of chrome black T to polyvinylidene fluoride in the color developing reagent is 1:6; unfold the positive electrode plate; apply the color developing reagent to the positive electrode plate to form a coating, and the coating is located in the central area of ​​the positive electrode plate. The coating is carried out in the coating area of ​​the coating location. There is one coating area, the area of ​​the coating area is 36 mm*4 mm, and the spraying amount of the coating area is 12 mg.

[0066] Example 4: Disassemble the battery cell and take out the positive electrode sheet in the battery cell; prepare a color developing reagent, the color developing reagent includes chrome black T and polyvinylidene fluoride, and the mass ratio of chrome black T to polyvinylidene fluoride in the color developing reagent is 1:7; unfold the positive electrode sheet; apply the color developing reagent to the positive electrode sheet to form a coating area, which is located in the central area of ​​the positive electrode sheet. Apply the coating area at the coating area, there is 1 coating area, the area of ​​the coating area is 36mm*4mm, and the spraying amount of the coating area is 12mg.

[0067] Example 5: Disassemble the battery cell and take out the positive electrode sheet in the battery cell; prepare a color developing reagent, the color developing reagent includes chrome black T and polyvinylidene fluoride, and the mass ratio of chrome black T to polyvinylidene fluoride in the color developing reagent is 1:8; unfold the positive electrode sheet; apply the color developing reagent to the positive electrode sheet to form a coating area, which is located in the central area of ​​the positive electrode sheet. Apply the coating area at the coating area, there is 1 coating area, the area of ​​the coating area is 36mm*4mm, and the spraying amount of the coating area is 12mg.

[0068] Example 6: Disassemble the battery cell and take out the positive electrode sheet in the battery cell; prepare a color developing reagent, the color developing reagent includes chrome black T and polyvinylidene fluoride, and the mass ratio of chrome black T to polyvinylidene fluoride in the color developing reagent is 1:9; unfold the positive electrode sheet; apply the color developing reagent to the positive electrode sheet to form a coating area, which is located in the central area of ​​the positive electrode sheet. Apply the coating area at the coating area, there is 1 coating area, the area of ​​the coating area is 36mm*4mm, and the spraying amount of the coating area is 12mg.

[0069] Example 7: Disassemble the battery cell and take out the positive electrode sheet in the battery cell; prepare a color developing reagent, the color developing reagent includes chrome black T and polyvinylidene fluoride, and the mass ratio of chrome black T to polyvinylidene fluoride in the color developing reagent is 1:7; unfold the positive electrode sheet; apply the color developing reagent to the positive electrode sheet to form a coating area, which is located in the central area of ​​the positive electrode sheet. Apply the coating area at the coating area, there is 1 coating area, the area of ​​the coating area is 36mm*4mm, and the spraying amount of the coating area is 12mg.

[0070] Example 8: Disassemble the battery cell and take out the positive electrode sheet in the battery cell; prepare a color developing reagent, the color developing reagent includes chrome black T and polyvinylidene fluoride, and the mass ratio of chrome black T to polyvinylidene fluoride in the color developing reagent is 1:7; unfold the positive electrode sheet; apply the color developing reagent to the positive electrode sheet to form a coating area, which is located in the central area of ​​the positive electrode sheet. Apply the coating area at the coating area, there are 2 coating areas, the area of ​​the coating area is 18mm*4mm, and the spraying amount of each coating area is 6mg.

[0071] Example 9: Disassemble the battery cell and take out the positive electrode sheet in the battery cell; prepare a color developing reagent, the color developing reagent includes chrome black T and polyvinylidene fluoride, and the mass ratio of chrome black T to polyvinylidene fluoride in the color developing reagent is 1:7; unfold the positive electrode sheet; apply the color developing reagent to the positive electrode sheet to form a coating area, which is located in the central area of ​​the positive electrode sheet. Apply the coating area at the coating area, there are 4 coating areas, the area of ​​the coating area is 9mm*4m, and the spraying amount of each coating area is 3mg.

[0072] Comparative Example 1: Disassemble the battery cell and take out the positive electrode sheet in the battery cell; prepare a color developing reagent, the color developing reagent includes chrome black T and polyvinylidene fluoride, and the mass ratio of chrome black T to polyvinylidene fluoride in the color developing reagent is 1:2; unfold the positive electrode sheet; apply the color developing reagent to the positive electrode sheet to form a coating area, which is located in the central area of ​​the positive electrode sheet. Apply the coating area at the coating area, there is 1 coating area, the area of ​​the coating area is 36mm*4mm, and the spraying amount of the coating area is 12mg.

[0073] Comparative Example 2: Disassemble the battery cell and take out the positive electrode sheet in the battery cell; prepare a color developing reagent, the color developing reagent includes chrome black T and polyvinylidene fluoride, and the mass ratio of chrome black T to polyvinylidene fluoride in the color developing reagent is 1:3; unfold the positive electrode sheet; apply the color developing reagent to the positive electrode sheet to form a coating area, which is located in the central area of ​​the positive electrode sheet. Apply the coating area at the coating area, there is 1 coating area, the area of ​​the coating area is 36mm*4mm, and the spraying amount of the coating area is 12mg.

[0074] Comparative Example 3: Disassemble the battery cell and take out the positive electrode sheet in the battery cell; prepare a color developing reagent, the color developing reagent includes chrome black T and polyvinylidene fluoride, and the mass ratio of chrome black T to polyvinylidene fluoride in the color developing reagent is 1:10; unfold the positive electrode sheet; apply the color developing reagent to the positive electrode sheet to form a coating area, which is located in the central area of ​​the positive electrode sheet. Apply the coating area at the coating area, there is 1 coating area, the area of ​​the coating area is 36mm*4mm, and the spraying amount of the coating area is 12mg.

[0075] The color development results are shown in Table 1.

[0076] Table 1 Color development results and color development reagents of Examples 1-9 and Comparative Examples 1-3

[0077] name Color rendering Color development time Example 1 Light color 445-500s Example 2 Light color 380-468s Example 3 Light color 250-338s Example 4 Good color rendering 150-223s Example 5 Light color 128-175s Example 6 Light color 50-108s Example 7 Good color rendering 150-189s Example 8 Good color rendering 86-131s Example 9 Good color rendering 54-93s Comparative Example 1 No color - Comparative Example 2 No color - Comparative Example 3 No color -

[0078] Color development time refers to the time from coating completion to the start of color development to the time from coating completion to the time from no longer obvious color development. As can be seen from Table 1, embodiments 1-9 can all develop color, and the time from coating completion to the start of color development is no more than 445s, and the color development speed is fast. It is illustrated that the technical scheme of the present invention is short in test time relative to the prior art. In embodiment 4, embodiment 7, embodiment 8 and embodiment 9, the mass ratio of chrome black T and polyvinylidene fluoride in the color developing reagent is 1:7, and the color development effect is good. It is illustrated that the mass ratio of chrome black T and polyvinylidene fluoride is 1:7, and the color development effect is best. In comparative example 1 and comparative example 2, the mass ratios of chrome black T and polyvinylidene fluoride are 1:2 and 1:3 respectively, and the content of chrome black T is too high, resulting in excessive viscosity of the developer, and the color of the coating area is covered by the original black of chrome black T, and no color development. In comparative example 3, the mass ratio of chrome black T and polyvinylidene fluoride is 1:10, and the content of chrome black T is too low, and the color of the developer is not obvious, and the color development change cannot be distinguished, and no color development is performed. In Example 7, there is 1 coating area, the area of ​​the coating area is 36mm*4mm, the spraying amount of each coating area is 12mg, the color development effect is good, the time to start color development is 150s, the color development speed is fast, and the test time of the battery cell electrolyte infiltration degree test is short. In Example 8, there are 2 coating areas, the area of ​​the coating area is 18mm*4mm, the spraying amount of each coating area is 6mg, the color development effect is good, the time to start color development is 86s, the color development speed is fast, and the test time of the battery cell electrolyte infiltration degree test is short. In Example 9, there are 4 coating areas, the area of ​​the coating area is 9mm*4m, the spraying amount of each coating area is 3mg, the color development effect is good, the time to start color development is 54s, the color development speed is fast, and the test time of the battery cell electrolyte infiltration degree test is short.

[0079] In a second aspect, the present invention provides a method for screening battery cells, using the above-mentioned method for testing the degree of electrolyte infiltration of battery cells to test the degree of electrolyte infiltration of battery cells to obtain test results, and screening battery cells with complete infiltration according to the test results.

[0080] By adopting the above technical solution, it is possible to screen out battery cells with complete infiltration degree. The operation is simple, the test speed is fast, the production turnover cycle of the battery cells is shortened, the accuracy of the test is improved, it is intuitive and effective, and no additional special equipment is required.

[0081] Although the present invention has been illustrated and described with reference to certain preferred embodiments of the present invention, it should be understood by those skilled in the art that the above is a further detailed description of the present invention in conjunction with specific embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. Those skilled in the art may make various changes in form and details, including making several simple deductions or substitutions, without departing from the spirit and scope of the present invention.

Claims

1. A method for testing the degree of electrolyte infiltration of a battery cell, characterized in that: include: Disassembling the battery cell and taking out the positive electrode sheet in the battery cell; A color developing reagent is prepared, wherein the color developing reagent comprises chrome black T and an organic binder, wherein the mass ratio of chrome black T to the organic binder in the color developing reagent is 1:4 to 1:9; Unfolding the positive electrode sheet; Applying the color developing reagent to the positive electrode plate to form a coating area, wherein the coating area is located in the central area of ​​the positive electrode plate; It is determined whether the coating area is wine red. If so, the electrolyte completely infiltrates the battery cell. If not, the electrolyte does not completely infiltrate the battery cell.

2. The method for testing the degree of electrolyte infiltration of a battery cell according to claim 1, characterized in that: The coating portion includes two coating regions, which are of equal length and are spaced apart along the length direction of the positive electrode sheet.

3. The method for testing the degree of electrolyte infiltration of a battery cell according to claim 2, characterized in that: The coating amount of the color developing reagent in each of the coating areas is 6 to 15 mg.

4. The method for testing the degree of electrolyte wetting of a battery cell according to claim 1, characterized in that: The coating area includes four coating regions, which are of equal length and are arranged at intervals along the length direction of the positive electrode sheet, and the intervals between two adjacent coating regions are equal.

5. The method for testing the degree of electrolyte infiltration of a battery cell according to claim 4, characterized in that: The coating amount of the color developing reagent in each of the coating areas is 2 to 4 mg.

6. The method for testing the degree of electrolyte infiltration of a battery cell according to claim 1, characterized in that: The coating portion includes a coating area, and the coating area is arranged along the length direction of the positive electrode plate.

7. The method for testing the degree of electrolyte infiltration of a battery cell according to claim 6, characterized in that: The coating amount of the color developing reagent in the coating area is 10 to 60 mg.

8. The method for testing the degree of electrolyte infiltration of a battery cell according to claim 1, characterized in that: The color developing reagent also includes: N-methylpyrrolidone, the mass ratio of the organic binder to the N-methylpyrrolidone is 3:125-1:

100.

9. The method for testing the degree of electrolyte infiltration of a battery cell according to any one of claims 2 to 5, characterized in that: Also includes: It is determined whether each of the coating areas is wine red. If so, the electrolyte evenly infiltrates the battery cell. If not, the electrolyte unevenly infiltrates the battery cell.

10. A method for screening battery cells, comprising: testing the degree of electrolyte infiltration of the battery cells using the method for testing the degree of electrolyte infiltration of the battery cells as described in any one of claims 1 to 9 to obtain a test result, and screening battery cells with complete infiltration according to the test result.

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