Method for judging consistency of pole piece and verification method

Abstract

The application provides a method for judging the consistency of an electrode sheet and a verification method, which comprises the following steps: selecting at least three measurement groups on the electrode sheet, the distance between the measurement groups and the lug of the electrode sheet is greater than a preset distance, the measurement group comprises at least three measurement points, and the distance between the measurement points is equal interval; performing linear fitting on the first impedance values of all the measurement points in each measurement group to generate a fitting straight line corresponding to each measurement group; obtaining a second impedance value corresponding to each measurement group according to the fitting straight line corresponding to each measurement group; obtaining the difference between each two second impedance values according to the second impedance values corresponding to each measurement group; and judging the consistency of the electrode sheet according to the difference of the difference values. The method for judging the consistency of the electrode sheet can quickly judge the consistency of the electrode sheet, simplifies the test steps, reduces the cost of the measuring equipment, and is more accurate in judgment.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion battery research and development, and in particular to a method for judging the consistency of an electrode sheet and a verification method. BACKGROUND

[0002] At present, relying on the background of global energy revolution and a series of favorable policies on new energy vehicles issued by governments of some countries and regions, the lithium ion battery industry is booming. In addition, lithium ion batteries also dominate in the fields of portable electronics and energy storage. According to statistics, the global lithium ion battery industry scale reached 66 billion US dollars in 2022, showing a huge market value.

[0003] The quality of lithium ion batteries is affected by the consistency of the electrode sheet, so many methods for judging the consistency of the electrode sheet have emerged. Currently, some methods for judging the consistency of the electrode sheet divide the electrode sheet into several regions, measure the impedance value of each region by a measuring device, and then compare it with the set threshold to judge the consistency of the electrode sheet. Others select sampling points on the electrode sheet, measure the square resistance value of each sampling point by a measuring device, calculate the average square resistance value of each sampling point, and then compare it with the standard square resistance to judge the consistency of the electrode sheet. The above-mentioned methods for judging the consistency of the electrode sheet usually require a multi-probe measuring device to measure the capacitance value or resistance value, and then calculate and compare the measured capacitance value or resistance value to judge the consistency of the electrode sheet. The steps of measurement and judgment are complicated, the cost is high, and only the capacitance value or resistance value on the surface of the electrode sheet is measured, so the judgment of the consistency of the electrode sheet is not accurate enough. SUMMARY

[0004] The present application proposes a method for judging the consistency of an electrode sheet to solve the above-mentioned problems. The method can quickly judge the consistency of the electrode sheet, simplify the testing steps, reduce the cost of the measuring device, and make the judgment of the consistency of the electrode sheet more accurate.

[0005] According to a first aspect, a method for judging the consistency of an electrode sheet is provided in an embodiment, comprising: selecting at least three measurement groups on the electrode sheet, the distance between the measurement group and the lug of the electrode sheet being greater than a preset distance; the measurement group comprising at least three measurement points, the distance between the measurement points being equal interval; measuring the first impedance value of each measurement point; linear fitting is performed according to the first impedance value of all measurement points in each measurement group to generate a fitting straight line corresponding to each measurement group; obtaining the second impedance value corresponding to each measurement group according to the fitting straight line corresponding to each measurement group; obtaining the difference value between each two second impedance values according to the second impedance value corresponding to each measurement group; calculating the difference between the difference values, and judging the consistency of the electrode sheet according to the difference between the difference values.

[0006] In some embodiments, the method of linear fitting according to the first impedance values of all the measuring points in each measuring group is linear fitting by using the original software, wherein the X axis is the number of small sections, the number of small sections is the number of small sections into which the tab is divided into at equal intervals, and the Y axis is the resistance value.

[0007] In some embodiments, the preset distance is 30 cm.

[0008] In some embodiments, the distance between each measuring point is 3 cm.

[0009] In some embodiments, the method of measuring the first impedance value of each measuring point by using a single resistance probe and a measuring instrument includes connecting one measuring head of the measuring instrument to the tab lug of the tab and connecting the other measuring head to the single resistance probe, and placing the single resistance probe above the tab.

[0010] In some embodiments, the single resistance probe is a cylindrical single resistance probe, and the bottom of the cylindrical single resistance probe is provided with four fan-shaped protrusions.

[0011] In some embodiments, the method of obtaining the second impedance value corresponding to each measuring group according to the fitting straight line corresponding to each measuring group includes taking the intersection point of the fitting straight line corresponding to each measuring group and the X axis value as the preset small section value as the intercept of the fitting straight line, and obtaining the second impedance value corresponding to each measuring group according to the intercept of the fitting straight line corresponding to each measuring group.

[0012] According to a second aspect, an embodiment provides a verification method of a method of judging the consistency of a tab, including: dividing the tab into a plurality of measuring sections at equal intervals, the measuring sections including the following resistance values: a vertical resistance value, a horizontal resistance value, and a copper foil resistance value; using a resistance element to establish a circuit model for judging the consistency of the tab according to the vertical resistance value, the horizontal resistance value, and the copper foil resistance value of each measuring section; using a two-probe method to measure the vertical resistance value of a measuring section, and using a four-probe method to measure the horizontal resistance value and the copper foil resistance value of each measuring section, respectively; using multi-sim software to establish an analog circuit model according to the circuit model, the vertical resistance value, the horizontal resistance value, and the copper foil resistance value; and verifying the method of judging the consistency of the tab based on the analog circuit model.

[0013] In some embodiments, the size of each measuring section is 5 cm.

[0014] In some embodiments, the vertical resistance value is 550 mΩ, the horizontal resistance value is 51 mΩ, and the copper foil resistance value is 3.5 mΩ.

[0015] According to the method of the above embodiment, by selecting at least three measurement groups on the pole piece, according to the second impedance value corresponding to each measurement group, the difference between each two second impedance values is obtained, and according to the difference of the calculated difference value, the consistency of the pole piece can be quickly judged; according to the measured combined impedance of the pole piece coating and the foil, the consistency of the pole piece is judged, so that the consistency of the pole piece is more accurate; using a single resistance probe and a measuring instrument to measure the first impedance value of each measurement point can reduce the cost of the measuring equipment and simplify the measurement steps; the single resistance probe is improved into a cylindrical single resistance probe, and the four fan-shaped protrusions arranged at the bottom thereof can reduce the contact area of the resistance probe and the pole piece, reduce the contact impedance, and thus improve the accuracy of the consistency judgment of the pole piece. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 A flowchart of the pole piece consistency judgment method;

[0017] Figure 2 A schematic diagram of measuring the first impedance value of each measurement point;

[0018] Figure 3 A structural schematic diagram of the cylindrical single resistance probe;

[0019] Figure 4 A structural schematic diagram of the fan-shaped protrusion;

[0020] Figure 5 A flowchart of obtaining the second impedance value corresponding to each measurement group;

[0021] Figure 6 A schematic diagram of a linear fitting straight line of the first impedance values of all measurement points of one measurement group;

[0022] Figure 7 A schematic diagram of a linear fitting straight line of the first impedance values of all measurement points of another measurement group;

[0023] Figure 8 A schematic diagram of a linear fitting straight line of the first impedance values of all measurement points of another measurement group;

[0024] Figure 9 A flowchart of the verification method;

[0025] Figure 10 A schematic diagram of one embodiment of the verification method;

[0026] Figure 11 A schematic diagram of another embodiment of the verification method;

[0027] Figure 12 A schematic diagram of the relationship between impedance and measurement section;

[0028] Figure 13A diagram showing the relationship between impedance increment and the measurement section;

[0029] Figure 14 A diagram showing another embodiment of the verification method;

[0030] Figure 15 A diagram showing another embodiment of the verification method. DETAILED DESCRIPTION

[0031] The application will be further described below in connection with the drawings. Like elements in different embodiments are denoted by like reference numerals. In the following description, many details are described in order to provide a more thorough understanding of the application. However, it will be apparent to one skilled in the art that some features, which are not necessary to an understanding of the application, can be omitted or substituted for others as appropriate. In some instances, well-known structures and functions have not been described in detail in order to avoid obscuring the application.

[0032] In addition, the features, operations or characteristics described in the specification can be combined in any appropriate manner to form various embodiments. Also, the steps or actions in the method description can be performed in any appropriate order, as is apparent to those skilled in the art, unless otherwise specified. Therefore, the various sequences in the specification and the drawings are merely for the purpose of clear description of one embodiment, and do not mean that the sequence is necessary to follow.

[0033] For the lithium ion electrode sheet coated with electrode material on the current collector foil, the existing electrode sheet consistency judgment method usually needs to cooperate with a multi-probe measurement device and a measuring instrument to measure the capacitance value or the resistance value, such as: the four-probe resistance is used to measure the square resistance, four probes are connected with the surface of the electrode sheet on the same side to measure the resistance, and after the capacitance value or the resistance value is measured, the measured capacitance value or resistance value is compared with the standard value to obtain the judgment result of the electrode sheet consistency. The measurement steps are very cumbersome, time-consuming and laborious, resulting in low efficiency of judging the electrode sheet consistency, and only the capacitance value or the resistance value of the surface of the electrode sheet is measured in the measurement, so that the judgment of the electrode sheet consistency is not accurate enough.

[0034] Based on the aforementioned problems, this invention proposes a method for determining electrode consistency. At least three measurement groups are selected on the electrode, each group including multiple measurement points. A linear fit is performed on the first impedance values ​​of all measurement points in each group to generate a fitted straight line for each test group. A second impedance value is obtained for each test group based on the fitted straight line. The difference between any two second impedance values ​​is obtained based on the second impedance values ​​for each test group. The consistency of the electrode is determined based on the difference in these differences. This method for determining electrode consistency provides a rapid assessment of electrode consistency, simplifies the testing process, reduces the cost of measurement equipment, and provides more accurate results.

[0035] Please refer to Figure 1 One embodiment of the present invention provides a method for determining electrode consistency, comprising:

[0036] S10: Select at least three measurement groups on the electrode, with the distance between the measurement group and the electrode tab of the electrode greater than a preset distance; the measurement group includes at least three measurement points, and the distance between the measurement points is equal.

[0037] In practical applications, multiple measurement groups are selected at different locations on the electrode. The number of measurement groups and measurement points in each group can be adjusted adaptively. It should be understood that the more measurement groups and measurement points selected, the more accurate the judgment of electrode consistency will be.

[0038] S20: Measure the first impedance value at each measurement point.

[0039] In some embodiments, a first impedance value is measured at each measurement point, such as Figure 2 As shown, the method for measuring the first impedance value at each measurement point using a single resistance probe 1 and a measuring instrument 2 includes: connecting one measuring head 21 of the measuring instrument 2 to the tab of the electrode, and connecting the other measuring head 22 to the single resistance probe 1, placing the single resistance probe 1 above the electrode, and the measuring instrument 2 being an ohmmeter.

[0040] like Figures 3-4 As shown, in some embodiments, the single resistance probe 1 is improved to a cylindrical single resistance probe 10. The cylindrical single resistance probe 10 is provided with four fan-shaped protrusions 11. The four fan-shaped protrusions 11 can reduce the contact area between the resistance probe and the electrode, reduce the contact impedance, and thus improve the accuracy of the electrode consistency judgment.

[0041] S30: Perform linear fitting based on the first impedance value of all measurement points in each measurement group to generate the fitting line corresponding to each measurement group.

[0042] In some embodiments, the method for generating a fitted straight line for each measurement group by linear fitting based on the first impedance values ​​of all measurement points in each measurement group includes: performing linear fitting using Origin software, where the X-axis represents the number of segments, which is the number of equally spaced segments into which the electrode is divided, and the Y-axis represents the impedance value. The number of segments can be adaptively adjusted as needed, and other tools can be selected for linear fitting as required. Origin software is a scientific plotting and data analysis software developed by OriginLab. Origin's data analysis functions include statistics, signal processing, curve fitting, and peak analysis.

[0043] S40: Based on the fitted straight line corresponding to each measurement group, obtain the second impedance value corresponding to each measurement group.

[0044] In some embodiments, such as Figure 5 As shown, the method for obtaining the second impedance value for each measurement group based on the fitted straight line for each measurement group includes:

[0045] S41: The intersection point of the fitted line corresponding to each measurement group and the X-axis value is a preset small segment value is taken as the intercept of the fitted line.

[0046] S42: Based on the intercept of the fitted straight line corresponding to each measurement group, obtain the second impedance value corresponding to each measurement group.

[0047] In some embodiments, three measurement groups are selected on the electrode, with the distance between the measurement group and the electrode tab being greater than or equal to 30 cm. Each measurement group includes four measurement points, with a distance of 3 cm between each measurement point. A single resistance probe 1 and a measuring instrument 2 are used to measure the first impedance value of each measurement point in each measurement group. The first impedance values ​​of the four measurement points in each measurement group are linearly fitted using Origine software, such as... Figures 6-8 As shown, the fitted straight lines corresponding to the three measurement groups A, B, and C are obtained respectively. Here, Equation represents the linear fitting equation, Weight represents the weight function, Ratio Sum of Squares represents the sum of squared differences, Pearson's r represents the correlation coefficient, Adj. R-Square represents the correction determination coefficient, Value represents the assumed value, Intercept represents the intercept, Slope represents the slope, and linear Fitting of represents the fitted straight line corresponding to each group. In this embodiment, because the distance between the selected three measurement groups and the electrode tabs is greater than or equal to 30cm (preset distance), the first impedance values ​​of all measurement points in the three measurement groups can be linearly fitted to a straight line. The preset distance value can be adaptively adjusted according to actual applications.

[0048] In some embodiments, the preset segment value is 6, and the value of each segment is 5 cm, as shown in FIG. 1. When X = 6, the distance from the tab of the pole piece is 30 cm. As can be seen from the figure, the distance from each selected measurement group to the tab of the pole piece is greater than 30 cm. The intersection point of the fitting straight line corresponding to the three measurement groups and X = 6 is taken as the intercept of the fitting straight line. The value of the Y axis corresponding to the intercept of each fitting straight line is the corresponding second impedance value R0. The second impedance value of each measurement group is the impedance value of the part of the pole piece covered by the measurement group. Figures 6-8

[0049] S50: According to the second impedance value corresponding to each test group, the difference between each two second impedance values is obtained.

[0050] S60: Calculate the difference between the differences, and judge the consistency of the pole piece according to the difference between the differences.

[0051] In some embodiments, three measurement groups A, B and C are selected on the pole piece. The first impedance values of all measurement points in the three measurement groups can be linearly fitted into a straight line, and the second impedance value corresponding to each measurement group is R0. The difference between each two second impedance values is calculated, the difference between the differences is calculated, and the consistency of the pole piece is judged by comparing the difference between the differences. According to the data shown in Table 1, the difference between A measurement group and B measurement group is 0.08, and the difference between C measurement group and B measurement group is 0.2. It is judged that the consistency of the latter section of the pole piece is worse than that of the former section. The method provided by the application can quickly judge the consistency of the entire pole piece.

[0052] Measurement group A B C [R0] 31.75 31.67 31.47

[0053] Table 1

[0054] Another embodiment of the application provides a verification method for judging the consistency of a pole piece, as shown in FIG. 2, comprising: Figure 9

[0055] S70: The pole piece is divided into multiple measurement sections with equal intervals, and the measurement sections include the following resistance values: vertical resistance value, horizontal resistance value and copper foil resistance value.

[0056] S80: According to the vertical resistance value, the horizontal resistance value and the copper foil resistance value of each measurement section, a circuit model for judging the consistency of the pole piece is established by using a resistance element.

[0057] ​​In practical applications, the electrode adopts a sandwich (dressing-foil-dressing) structure. During the measurement process, the current flows spherically when passing through the resistance probe. In some embodiments, only three resistance values—vertical resistance, lateral resistance, and copper foil resistance—are selected to establish a circuit model for judging electrode consistency. The reason is that after the current flows through the cylindrical single resistance probe 10, it splits laterally to the left and right and vertically to the right. The vertical current flows through the dressing and then through the copper foil below to the electrode tab. The lateral current is further split into a second lateral current and a second vertical current. The second vertical current flows downward through the dressing and then continues into the copper foil. The second lateral current continues to split in this way. Figure 10 As shown. The effectiveness of the method of the present invention can be verified by simply establishing a circuit model for judging the consistency of the electrode based on the equivalent values ​​of vertical resistance, horizontal resistance, and copper foil resistance.

[0058] In some embodiments, the electrode is divided into N equally spaced measurement segments, each segment being 5 cm in size. Each measurement segment has corresponding transverse material resistance, longitudinal material resistance, and transverse copper foil resistance, such as... Figure 11 As shown, a circuit model for determining electrode consistency is established using resistive elements.

[0059] S90: The vertical resistance value of a measurement segment is measured using a two-probe method, and the transverse resistance value and the copper foil resistance value of each measurement segment are measured using a four-probe method.

[0060] S100: Based on the circuit model, the vertical resistance value, the horizontal resistance value, and the copper foil resistance value, a simulation circuit model is established using Multisimilar software.

[0061] In some embodiments, the measured vertical resistance is 550mΩ, the lateral resistance is 51mΩ, and the copper foil resistance is 3.5mΩ. The analog circuit model built using Multisim software is as follows: Figure 14 As shown, Multis IM software is a Windows-based simulation tool suitable for board-level analog / digital circuit board design and possesses rich simulation analysis capabilities.

[0062] S110: Verify the method for judging electrode consistency based on the analog circuit model.

[0063] In some embodiments, based on Figure 14 The circuit model shown is used for verification. Figure 12 The graph shows the relationship between impedance and measurement segment, where the horizontal axis represents the measurement segment and the vertical axis represents the impedance value. Figure 13The relationship between the impedance increment and the measurement section is shown, wherein the horizontal coordinate represents the measurement section, and the vertical coordinate represents the impedance increment value. When the measurement distance of the measurement group is outside the sixth measurement section of the tab, the impedance value of each measurement point changes linearly, and the impedance value increases by 3.5 mΩ every time a measurement point is passed, which corresponds to the impedance value of the copper foil in the section. This indicates that after the measurement point is a certain distance (such as 30 cm) away from the tab, the transverse shunt of the dressing has little effect on the overall impedance value. Through this verification, it can be seen that if the tab consistency is good, the impedance values of all measurement points in each measurement group can be fitted into a straight line when the distance between the measurement group and the tab of the tab is greater than or equal to the preset distance. The results obtained by measuring the tab with good consistency should have linear characteristics. Figure 13 The impedance increment value ΔR is shown. It can be seen that if the tab consistency is good, the difference between the adjacent two measurement groups is small. Figure 14 The current values I(dc) corresponding to the nine measurement points measured based on the established analog circuit model are shown.

[0064] Since the dressing on the tab has a thickness, most of the existing measurement methods for judging the tab consistency only measure the surface resistance value of the dressing, which affects the accuracy of the tab consistency judgment. The method provided by the present application judges the tab consistency based on the measured combined impedance of the tab dressing and the foil, so that the judgment result is more accurate.

[0065] In some embodiments, as shown in Figure 15 When the measurement distance of the measurement group is in or outside the sixth measurement section (5 cm for each measurement section, so the sixth measurement section is 30 cm) of the tab, the front section of the cylindrical single resistance probe 10 can be regarded as an integral impedance value R0 in series with the copper foil impedance from the remaining section to the tab. The test results show that when X = 6, the impedance value corresponding to the measurement group is R0, which also verifies the feasibility of the method for obtaining the second impedance value in steps S41 and S42.

[0066] The above application of specific examples to the present application is only used to help understand the present application and does not limit the present application. For those skilled in the art to which the present application belongs, according to the idea of the present application, a number of simple deductions, deformations or substitutions can be made.

Claims

1. A method of determining electrode consistency, characterized by, The method comprises the following steps: selecting at least three measurement groups on the pole piece, the distance between the measurement groups and the lug of the pole piece being greater than a preset distance, the measurement groups comprising at least three measurement points, the distance between the measurement points being equal intervals; measuring the first impedance value of each measurement point; linear fitting is performed on the first impedance values of all measurement points in each measurement group to generate a fitting straight line corresponding to each measurement group; obtaining the second impedance value corresponding to each measurement group according to the fitting straight line corresponding to each measurement group; obtaining the difference between each two second impedance values according to the second impedance values corresponding to each measurement group; calculating the difference between the differences, and judging the consistency of the pole piece according to the difference between the differences; The method for measuring the first impedance value of each measurement point comprises: connecting one measurement head of a measuring instrument with the lug of the pole piece, and connecting the other measurement head with a single resistance probe, and placing the resistance probe above the pole piece. Wherein, when measuring the first impedance value of each measurement point, the resistance probe is placed at the position of the measurement point which needs to measure the first impedance value.

2. The method of claim 1, wherein, The method for linear fitting according to the first impedance values of each measurement point in each measurement group to generate a fitting straight line corresponding to each measurement group is: linear fitting is performed by using origin software, wherein the X-axis is the number of small sections, the number of small sections is the number of small sections obtained by dividing the pole piece into equal intervals, and the Y-axis is the resistance value.

3. The method of claim 1, wherein, The preset distance is 30 cm.

4. The method of claim 1, wherein, The distance between each measurement point is 3 cm.

5. The method of claim 1, wherein, The single resistance probe is a cylindrical single resistance probe, and the bottom of the cylindrical single resistance probe is provided with four fan-shaped protrusions.

6. The method of claim 2, wherein, The method for obtaining the second impedance value corresponding to each measurement group according to the fitting straight line corresponding to each measurement group comprises: taking the intersection point of the fitting straight line corresponding to each measurement group and the X-axis value as the preset small section value as the intercept of the fitting straight line; obtaining the second impedance value corresponding to each measurement group according to the intercept of the fitting straight line corresponding to each measurement group.

7. A method of verifying a method of judging electrode consistency, characterized by, The method comprises the following steps: dividing the pole piece into a plurality of measurement sections with equal intervals, the measurement sections comprising the following resistance values: vertical resistance value, horizontal resistance value and copper foil resistance value; establishing a circuit model for judging the consistency of the pole piece by using resistance elements according to the vertical resistance value, the horizontal resistance value and the copper foil resistance value of each measurement section; measuring the vertical resistance value of a measurement section by using a two-probe method, and measuring the horizontal resistance value and the copper foil resistance value of each measurement section by using a four-probe method; establishing an analog circuit model by using multisim software according to the circuit model, the vertical resistance value, the horizontal resistance value and the copper foil resistance value; verifying the method for judging the consistency of the pole piece based on the analog circuit model.

8. The authentication method of claim 7, wherein, The size of each measurement section is 5 cm.

9. The authentication method of claim 8, wherein, The vertical resistance value is 550 mΩ, the horizontal resistance value is 51 mΩ, and the copper foil resistance value is 3.5 mΩ.

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