A method for evaluating the effectiveness of a button battery made based on mass-produced batteries

Abstract

The present invention discloses a method for evaluating the effectiveness of a button cell fabricated based on mass-produced batteries. The method includes: performing constant charge and discharge volume on the mass-produced batteries; disassembling the mass-produced batteries; fabricating button cells using some of the positive electrode sheets of the mass-produced batteries; charging the button cells; recording the first-week charging capacity of the button cells and calculating the first-week charging capacity per unit area of the positive electrode sheets of the button cells and the corresponding charging capacity per unit area of the mass-produced batteries; calculating the unit area capacity error rate of the button cells. If the absolute value of the unit area capacity error rate of the button cells is less than a preset value, the button cells are effectively usable. The advantages of the present invention are: providing a method for evaluating whether the button cells fabricated based on mass-produced batteries are effectively usable, avoiding affecting subsequent attenuation analysis, and improving the accuracy of the analysis results.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery testing, and more particularly to a method for evaluating the effectiveness of a button cell fabricated based on mass-produced batteries. Background Art

[0002] Due to the progress of technology and the development of society, people not only satisfy the basic requirements of food, clothing, housing, and transportation, but also have higher and higher requirements for the environment in which they live. The exhaust emissions of fuel-powered vehicles can cause serious air pollution. In order to protect the environment, countries have been vigorously developing new energy vehicles in recent years, among which new energy vehicles powered by lithium-ion batteries are particularly outstanding. During the use of lithium-ion batteries, battery attenuation will inevitably occur. For the analysis of battery attenuation, it is necessary to disassemble the battery and fabricate button cells from the positive and negative electrode sheets of the battery, and use the button cells for attenuation analysis. However, since the button cells are fabricated manually, damage may occur during the fabrication process, and the performance of button cells fabricated from the same materials by different personnel varies greatly. Therefore, it is difficult to ensure the effectiveness of the fabricated button cells, which affects subsequent attenuation analysis and leads to inaccurate analysis results. Currently, most in the industry focus on researching the cycle performance of lithium-ion batteries, and a small amount of research uses button cells to evaluate lithium battery materials after cycling. For example, a method for evaluating lithium-ion battery electrode materials after cycling using button cells disclosed in Chinese Patent Publication No. CN110927593A. However, there is currently no method for judging whether the button cells fabricated based on mass-produced batteries are effective and usable. Summary of the Invention

[0003] The technical problem to be solved by the present invention is that there is currently no method for judging whether the button cells fabricated based on mass-produced batteries are effective and usable, which affects subsequent attenuation analysis and leads to inaccurate analysis results.

[0004] The present invention solves the above technical problems by the following technical means: A method for evaluating the effectiveness of a button cell fabricated based on mass-produced batteries, the method comprising:

[0005] Step a: Performing constant current charge and discharge on the mass-produced battery;

[0006] Step b: Disassembling the mass-produced battery;

[0007] Step c: Fabricating a button cell using a part of the positive electrode sheet of the mass-produced battery;

[0008] Step d: Charging the button cell;

[0009] Step e: Recording the first-week charging capacity of the button cell and calculating the first-week charging capacity per unit area of the positive electrode sheet of the button cell and the corresponding charging capacity per unit area of the mass-produced battery;

[0010] Step f: Calculate the capacity error rate per unit area of the button cell. If the absolute value of the capacity error rate per unit area of the button cell is less than the preset value, the button cell is effectively available.

[0011] The present invention calculates the first-week charging capacity per unit area of the positive electrode sheet of the button cell and the corresponding charging capacity per unit area of the mass-produced battery, obtains the capacity error rate per unit area of the button cell based on the first-week charging capacity per unit area of the positive electrode sheet of the button cell and the corresponding charging capacity per unit area of the mass-produced battery, uses the absolute value of the error rate to judge whether the button cell is effectively available, makes up for the gap in the prior art, provides a method for judging whether the button cell made based on the mass-produced battery is effectively available, avoids affecting subsequent attenuation analysis, and improves the accuracy of the analysis results.

[0012] Further, the step a includes:

[0013] Charge the mass-produced battery with a constant current. After it is fully charged, discharge the mass-produced battery with a constant current to the discharge cut-off voltage.

[0014] Furthermore, the constant current is equal to 0.1 times the rated capacity of the mass-produced battery.

[0015] Furthermore, the rated capacity of the mass-produced battery is 20 Ah, the constant current is 2 A, and the discharge cut-off voltage is 2 V. Charge the mass-produced battery with 2 A and record the charging capacity of the mass-produced battery. After it is fully charged, discharge the mass-produced battery with 2 A to 2 V.

[0016] Further, the step b includes: Disassemble the mass-produced battery and measure the length and width of the positive electrode sheet of the mass-produced battery.

[0017] Further, the step c includes: Use a part of the positive electrode sheet of the mass-produced battery to make the positive electrode sheet of the button cell. The negative electrode in the button cell is a lithium metal sheet. According to the diameter of the positive electrode sheet of the button cell, use the circular area formula to calculate the area of the positive electrode sheet of the button cell.

[0018] Further, during the charging process of the button cell in step d, the charging current rate of the button cell is consistent with the charging current rate during the constant volume of the corresponding mass-produced battery.

[0019] Furthermore, in step d, the charging current of the button cell is obtained by using the formula I = 0.1 * C * S / (a * b * 2), where C is the rated capacity of the mass-produced battery, S is the area of the positive electrode sheet of the button cell, and a and b are the length and width of the positive electrode sheet of the mass-produced battery respectively.

[0020] Further, the step e includes:

[0021] Using the formula C k = C 1 / S calculates the first-week charging capacity per unit area of the cathode sheet of a button cell, where C 1 is the first-week charging capacity of the cathode sheet of the button cell, and S is the area of the cathode sheet of the button cell;

[0022] Using the formula C l = C c / (a * b * 2) to calculate the charging capacity per unit area of the corresponding mass-produced battery, where C c is the charging capacity of the mass-produced battery, and a and b are the length and width of the cathode sheet of the mass-produced battery respectively.

[0023] Further, the step f includes:

[0024] Using the formula P = (C k - C l ) / C l to calculate the capacity error rate per unit area of the button cell;

[0025] If the absolute value of the capacity error rate P per unit area of the button cell < 1.5%, then the button cell is effectively usable.

[0026] The advantages of the present invention are as follows:

[0027] (1) The present invention calculates the first-week charging capacity per unit area of the cathode sheet of a button cell and the charging capacity per unit area of the corresponding mass-produced battery, obtains the capacity error rate per unit area of the button cell based on the first-week charging capacity per unit area of the cathode sheet of the button cell and the charging capacity per unit area of the corresponding mass-produced battery, and uses the absolute value of the error rate to determine whether the button cell is effectively usable, filling the gap in the prior art, providing a method for judging whether a button cell made based on a mass-produced battery is effectively usable, avoiding affecting subsequent attenuation analysis, and improving the accuracy of the analysis results.

[0028] (2) During the first-week discharge process of the button cell, lithium ions in the negative lithium sheet will supplement the lithium lost in the positive electrode, making the charging capacity in the second week higher than its first-week charging capacity. Therefore, the present invention uses the first-week charging capacity to calculate the capacity per unit area, and the calculation result is relatively accurate and reliable.

[0029] (3) Since the battery capacity depends on the capacity of the cathode sheet, the present invention calculates the error rate using the first-week charging capacity per unit area of the cathode sheet of the button cell and the charging capacity per unit area of the corresponding mass-produced battery, and the calculation result is relatively accurate and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flowchart of a method for judging the effectiveness of a button cell made based on a mass-produced battery disclosed in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] As Figure 1 shown, a method for evaluating the effectiveness of a button cell made from mass-produced batteries, the method comprising:

[0033] S1. Perform constant current charge and discharge on a mass-produced battery with a rated capacity of 20 Ah. The charging current is 0.1 * 20 = 2 A, and record the charging capacity of the mass-produced battery as 20.1 Ah. Then discharge the battery to 2 V (discharge cut-off voltage) at 2 A.

[0034] S2. Disassemble the mass-produced battery and measure the length and width of the positive electrode plate of the mass-produced battery. In this embodiment, the length of the positive electrode plate of the mass-produced battery is 2556 mm, and the width is 123 mm.

[0035] S3. Use a part of the positive electrode plate of the mass-produced battery to make 5 button cells. The negative electrode in the button cell is a lithium metal sheet, and the diameter of the positive electrode plate of the button cell is 12 mm. Calculate the area S of the positive electrode plate of the button cell = π * 6 mm * 6 mm = 113.1 mm 2 .

[0036] S4. Charge the button cell. To ensure that the charging current rate of the button cell is consistent with the charging current rate during the constant current charging of the corresponding mass-produced battery, where C is the rated capacity of the mass-produced battery, S is the area of the positive electrode plate of the button cell, and a and b are the length and width of the positive electrode plate of the mass-produced battery respectively. It should be noted that the positive electrode plate of the button cell is single-sided, and the corresponding positive electrode plate of the mass-produced battery is double-sided. Therefore, the area of the corresponding positive electrode plate of the mass-produced battery = length of the battery positive electrode plate * width * 2 = 2556 * 123 * 2.

[0037] S5. Record the first-week charging capacity of the positive electrode plates of the 5 button cells, and calculate the first-week charging capacity per unit area of the positive electrode plate of the button cell = first-week charging capacity of the positive electrode plate of the button cell / area of the positive electrode plate of the button cell. The charging capacity per unit area of the corresponding mass-produced battery = charging capacity of the mass-produced battery / (length of the positive electrode plate of the mass-produced battery * width * 2). The above calculation results are shown in Table 1.

[0038] Table 1 First-week charging capacity of button cells and error rate of capacity per unit area

[0039]

[0040]

[0041] S6. According to the first-week charging capacity per unit area of the button cell and the charging capacity per unit area of the mass-produced battery, calculate the capacity error rate per unit area of the button cell = (the first-week charging capacity per unit area of the button cell - the charging capacity per unit area of the mass-produced battery) / the charging capacity per unit area of the mass-produced battery. The calculation results are shown in Table 1. The calculation results show that the absolute values of the error rates of Button Cells 1#, 2#, 3#, and 5# are <1.5% and are available, while the absolute value of the error rate of Button Cell 4# >1.5% and is not available.

[0042] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating the effectiveness of a button cell made from mass-produced batteries, characterized in that, the method includes: Step a: Perform constant current charge and discharge to determine the capacity of the mass-produced battery; Step b: Disassemble the mass-produced battery; Step c: Use a part of the positive electrode sheet of the mass-produced battery to make a button cell; Step d: Charge the button cell; Step e: Record the first-week charging capacity of the button cell and calculate the first-week charging capacity per unit area of the positive electrode sheet of the button cell and the corresponding charging capacity per unit area of the mass-produced battery; Step e includes: Use the formula C k = C l / S to calculate the first-week charging capacity per unit area of the positive electrode sheet of a button battery, where C l is the first-week charging capacity of the positive electrode sheet of the button battery, and S is the area of the positive electrode sheet of the button battery; Use formula C l = C c / (a * b * 2) to calculate the charging capacity per unit area of the mass-produced battery. Among them, C c is the charging capacity of the mass-produced battery, and a and b are the length and width of the positive electrode plate of the mass-produced battery respectively; Step f: Calculate the unit area capacity error rate of the button cell. If the absolute value of the unit area capacity error rate of the button cell is less than the preset value, the button cell is effectively usable; Step f includes: Calculate the capacity error rate per unit area of the button cell using the formula P=(C k -C l ) / C l . If the absolute value of the unit area capacity error rate P of the button cell < 1.5%, the button cell is effectively usable.

2. The method for evaluating the effectiveness of a button cell made from mass-produced batteries according to claim 1, characterized in that, the said Step a includes: Charge the mass-produced battery with a constant current, and after it is fully charged, discharge the mass-produced battery with a constant current to the discharge cut-off voltage.

3. The method for evaluating the effectiveness of a button cell made from mass-produced batteries according to claim 2, characterized in that, the said constant current is equal to 0.1 times the rated capacity of the mass-produced battery.

4. The method for evaluating the effectiveness of a button cell made from mass-produced batteries according to claim 3, characterized in that, the rated capacity of the mass-produced battery is 20Ah, the constant current is 2A, the discharge cut-off voltage is 2V, charge the mass-produced battery with 2A, record the charging capacity of the mass-produced battery, and after it is fully charged, discharge the mass-produced battery with 2A to 2V.

5. The method for evaluating the effectiveness of a button cell made from mass-produced batteries according to claim 1, characterized in that, the said Step b includes: Disassemble the mass-produced battery and measure the length and width of the positive electrode sheet of the mass-produced battery.

6. The method for evaluating the effectiveness of a button cell made from mass-produced batteries according to claim 1, characterized in that, the said Step c includes: Use a part of the positive electrode sheet of the mass-produced battery to make the positive electrode sheet of the button cell. The negative electrode in the button cell is a lithium metal sheet. According to the diameter of the positive electrode sheet of the button cell, use the circular area formula to calculate the area of the positive electrode sheet of the button cell.

7. The method for evaluating the effectiveness of a button cell made from mass-produced batteries according to claim 1, characterized in that, during the charging process of the button cell in Step d, the charging current rate of the button cell is consistent with the charging current rate during the constant current charging of the corresponding mass-produced battery.

8. The method for evaluating the effectiveness of a button cell made from mass-produced batteries according to claim 7, characterized in that, in Step d, use the formula I = 0.1*C*S / (a*b*2) to obtain the charging current of the button cell, where C is the rated capacity of the mass-produced battery, S is the area of the positive electrode sheet of the button cell, and a and b are the length and width of the positive electrode sheet of the mass-produced battery respectively.

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