Method for accurately measuring resistance of pole piece coating

Abstract

The invention discloses a method for accurately measuring the resistance of a pole piece coating. The method comprises the following steps: S1, coating an insulating film with uniformly stirred slurry; s2, baking the insulating film coated with the slurry, and rolling to obtain an insulating film with a coating; s3, cutting and forming the insulating film with the coating; s4, four probes are adopted to measure the coating resistance on the insulating film; according to the method, the tiny difference between the coatings can be obviously distinguished, the influence of interface difference is avoided, the measurement result is stable, the accuracy is high, and the reliability is good.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium-ion batteries, and in particular relates to a method for accurately measuring the resistance of a pole piece coating. Background Art

[0002] The resistance of lithium-ion batteries is one of the important indicators for measuring battery performance. The resistance of lithium-ion batteries will have a direct impact on the capacity, cycle life and safety performance of lithium-ion batteries. The factors that affect the resistance of lithium-ion batteries include electrode materials, electrolytes, diaphragms, process levels, current collector resistance, pole sheet resistance, etc. Among them, the pole sheet resistance reflects the performance of electrode materials and the quality of the formula. The pole sheet is made by coating the current collector with slurry, and the slurry is made of a mixture of active material powder, binder, conductive agent, etc. Through the test of pole sheet resistance, the corresponding relationship between the pole sheet resistance and the resistance of lithium-ion batteries is found, and the resistance of lithium-ion batteries can be pre-evaluated. Not only that, through the test results of battery pole sheet resistance, on the one hand, the slurry coating process can be improved to achieve a rapid evaluation of the material system; on the other hand, pole sheets with large resistance values ​​can be screened and eliminated in a timely manner, so that they do not flow into the monomer manufacturing process, thereby improving the quality and performance of terminal products.

[0003] At present, the lithium battery industry often uses double probes or four probes to test the resistance of the electrode. When the two-probe method is used for testing, the terminals are placed at both ends of the sample, and the current at both ends of the sample is collected by inputting an AC voltage signal, and the sample resistance is obtained through a conversion relationship; when the four-probe method is used for testing, four probes are placed on the surface of the sample, and a DC signal is input to collect the voltage signal between the probes, and the sample resistance is obtained through a conversion relationship. However, the internal resistance of the electrode consists of three parts: coating resistance, current collector resistance, and interface resistance between coating and current collector. When the above two methods are used to test the internal resistance of the electrode, the three parts of resistance cannot be distinguished, and they are always affected by the current collector resistance and interface resistance, and the resistance change and law of the coating cannot be accurately analyzed. Moreover, the interface resistance in the electrode is often mistaken for the coating resistance because there is no specific measurement value, so the result measured by this method is inaccurate when used to replace the resistance of the coating.

[0004] Therefore, more accurate measurement of the resistance change of the coating and elimination or reduction of the influence of the current collector resistance and interface resistance are issues that need to be addressed. Summary of the invention

[0005] The object of the present invention is to provide a method for accurately measuring the resistance of a pole piece coating to solve at least one of the above-mentioned technical problems.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for accurately measuring the resistance of a pole piece coating comprises the following steps:

[0008] S1: Apply the stirred slurry onto the insulating film;

[0009] S2: baking the insulating film coated with the slurry, and then rolling it to obtain an insulating film with a coating;

[0010] S3: cutting and shaping the insulating film with the coating;

[0011] S4: using a four-probe probe to measure the coating resistance on the insulating film.

[0012] The present invention directly detects the coating resistance by coating an insulating film, thereby eliminating the influence of the collector resistance and the interface resistance and significantly distinguishing the slight differences between the coatings. The method is not only simple in process and good in operability, but also has good repeatability, and the measurement results are stable, accurate and reliable.

[0013] Furthermore, the insulating film is made of polyimide film, polyethylene film, polyvinylidene fluoride, polytetrafluoroethylene or polyethylene terephthalate.

[0014] Furthermore, the insulating film is first cleaned with a volatile organic solvent and dried before being coated with the slurry.

[0015] Furthermore, in step S2, the baking temperature is 60-120°C.

[0016] Furthermore, in step S3, the insulating film with the coating is cut into a rectangle with a length of 6 cm and a width of 2 cm.

[0017] Furthermore, in step S4, the cut and shaped insulating film with coating is placed under the four probes, the power of the tester is started, and the probes are slowly pressed down. The probes are pressed against the coating, and the pressure is controlled by a pressure gauge. After reaching the set pressure, the resistance data is read, which is the coating resistance value.

[0018] Furthermore, the pressure of the probe extrusion coating is 5-25 MPa.

[0019] Furthermore, the mass proportion of the conductive agent in the slurry is 2%-6%.

[0020] Furthermore, the slurry is applied to a thickness of 100-400 μm.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention directly detects the coating resistance by coating an insulating film, thereby eliminating the influence of the collector resistance and the interface resistance and significantly distinguishing the slight differences between the coatings. The method is not only simple in process and good in operability, but also has good repeatability, and the measurement results are stable, accurate and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of a method for accurately measuring the resistance of the electrode coating in this embodiment.

[0024] Figure 2 The resistance relationship diagram of the electrode and coating with different proportions of conductive agent formulations.

[0025] Figure 3 The resistance relationship diagram of the electrode and coating under different pressures.

[0026] Figure 4 The resistance relationship diagram of the electrode and coating with different slurry thicknesses. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] like Figure 1 As shown, this embodiment provides a method for accurately measuring the resistance of a pole piece coating, comprising the following steps:

[0029] S1: Apply the stirred slurry onto the insulating film;

[0030] S2: baking the insulating film coated with the slurry, and then rolling it to obtain an insulating film with a coating;

[0031] S3: cutting and shaping the insulating film with the coating;

[0032] S4: using a four-probe probe to measure the coating resistance on the insulating film.

[0033] The present invention directly detects the coating resistance by coating an insulating film, thereby eliminating the influence of the collector resistance and the interface resistance and significantly distinguishing the slight differences between the coatings. The method is not only simple in process and good in operability, but also has good repeatability, and the measurement results are stable, accurate and reliable.

[0034] Furthermore, the insulating film is made of polyimide film, polyethylene film, polyvinylidene fluoride, polytetrafluoroethylene or polyethylene terephthalate, preferably polytetrafluoroethylene.

[0035] Furthermore, before the insulating film is coated with the slurry, it is first cleaned with a volatile organic solvent and dried, and the organic solvent may be alcohol.

[0036] Further, in step S2, the baking temperature is 60-120°C, preferably 80°C.

[0037] Furthermore, in step S3, the insulating film with the coating is cut into a rectangle with a length of 6 cm and a width of 2 cm.

[0038] Furthermore, in step S4, the cut and shaped insulating film with coating is placed under the four probes, the power of the tester is started, and the probes are slowly pressed down. The probes are pressed against the coating, and the pressure is controlled by a pressure gauge. After reaching the set pressure, the resistance data is read, which is the coating resistance value.

[0039] Furthermore, the pressure of the probe extrusion coating is 5-25 MPa, preferably 15 MPa.

[0040] Furthermore, the mass proportion of the conductive agent in the slurry is 2%-6%, and the specific mass proportion of the conductive agent is determined according to the actual mass proportion of the conductive agent in the coating to be measured. For example, the mass proportion of the conductive agent in the coating to be tested is 3%. In this solution, the mass proportion of the conductive agent in the slurry applied to the insulating film is 3%. The conductive agent ratio in the present invention refers to the mass proportion of the conductive agent in the slurry.

[0041] Furthermore, the thickness of the slurry when applied is 100-400μm. In the present method, the specific slurry application thickness is determined according to the actual slurry application thickness of the coating to be measured. For example, if the slurry application thickness of the coating to be tested is 400μm, then in the present solution, the slurry application thickness of the produced coating is set to 400μm.

[0042] Example 1

[0043] The method for accurately measuring the resistance of the electrode coating comprises the following steps:

[0044] A slurry is prepared and evenly coated on a polytetrafluoroethylene insulating film, and then baked and rolled to obtain a coated polytetrafluoroethylene insulating film. The coated polytetrafluoroethylene insulating film is cut into rectangular sheets with a length of 6 cm and a width of 2 cm. The coating resistance on the polytetrafluoroethylene insulating film is measured using a four-probe. This embodiment includes 5 subdivision experiments, the difference being that the slurry settings are different, that is, 5 groups of slurries are set. The difference between these 5 groups of slurries is that the mass proportions of the conductive agent are 2%, 3%, 4%, 5%, and 6%, respectively. When measuring the coating resistance of the coated polytetrafluoroethylene insulating film made of the 5 groups of slurries, each group is measured three times, and the average value and standard deviation of the coating resistance are calculated.

[0045] Example 2

[0046] The method for accurately measuring the resistance of the electrode coating comprises the following steps:

[0047] A slurry is prepared and evenly coated on a polytetrafluoroethylene insulating film, and then baked and rolled to obtain a polytetrafluoroethylene insulating film with a coating. The polytetrafluoroethylene insulating film with a coating is cut into a rectangular sheet with a length of 6 cm and a width of 2 cm. Four probes are used to measure the coating resistance on the polytetrafluoroethylene insulating film. This embodiment includes 5 subdivision experiments, the difference being that the extrusion pressure of the probe on the coating is different, that is, when measuring the resistance, the extrusion pressure of the probe on the coating is set to 5 groups, and the 5 groups of pressures are 5 MPa, 10 MPa, 15 MPa, 20 MPa, and 25 MPa, respectively. Under each group of pressures, the coating resistance is measured three times, and the average value and standard deviation of the coating resistance are calculated.

[0048] Example 3

[0049] The method for accurately measuring the resistance of the electrode coating comprises the following steps:

[0050] A slurry is prepared and evenly coated on a polytetrafluoroethylene insulating film, and then baked and rolled to obtain a coated polytetrafluoroethylene insulating film. The coated polytetrafluoroethylene insulating film is cut into rectangular sheets with a length of 6 cm and a width of 2 cm. A four-probe is used to measure the coating resistance on the polytetrafluoroethylene insulating film. This embodiment includes 4 subdivision experiments, the difference being that the slurry coating thickness is different, that is, when the slurry is coated, 4 groups of coating thicknesses are set, and the 4 groups of coating thicknesses are 100 μm, 200 μm, 300 μm, and 400 μm, respectively. When measuring the coating resistance of the four groups of coated polytetrafluoroethylene insulating films coated with slurries of different thicknesses, each group is measured three times, and the average value and standard deviation of the coating resistance are calculated.

[0051] Comparative Example 1

[0052] Prepare the slurry, evenly apply it on the aluminum foil, and then bake and roll to obtain the electrode. The electrode is cut into a rectangular sheet with a length of 6 cm and a width of 2 cm. Four probes are used to measure the electrode resistance. Among them, this comparative example includes 5 subdivision experiments. The difference lies in the different slurry settings, that is, 5 groups of slurries are set. The difference between these 5 groups of slurries is that the mass proportion of the conductive agent is 2%, 3%, 4%, 5%, and 6%, respectively. When measuring the resistance of the electrode made of these 5 groups of slurries, each group is measured three times, and the average value and standard deviation of the resistance are calculated.

[0053] Comparative Example 2

[0054] Prepare the slurry, evenly apply it on the aluminum foil, and then bake and roll to obtain the electrode. Cut the electrode into a rectangular sheet with a length of 6 cm and a width of 2 cm, and use four probes to measure the electrode resistance. Among them, this comparative example includes 5 subdivision experiments. The difference lies in the different extrusion pressures of the probes on the coating, that is, when measuring the resistance, the extrusion pressures of the probes on the coating are set to 5 groups, and the 5 groups of pressures are 5MPa, 10MPa, 15MPa, 20MPa, and 25MPa, respectively. Under each group of pressure, measure the electrode resistance three times, and calculate the average value and standard deviation of the electrode resistance.

[0055] Comparative Example 3

[0056] Prepare the slurry, evenly apply it on the aluminum foil, and then bake and roll to obtain the electrode. The electrode is cut into a rectangular sheet with a length of 6 cm and a width of 2 cm. Four probes are used to measure the electrode resistance. Among them, this comparative example includes 4 subdivision experiments. The difference lies in the different slurry coating thicknesses. That is, when applying the slurry, 4 groups of coating thicknesses are set, and the 4 groups of coating thicknesses are 100μm, 200μm, 300μm, and 400μm, respectively. When measuring the resistance of the four groups of electrode sheets coated with slurry of different thicknesses, each group is measured three times, and the average value and standard deviation of the coating resistance are calculated.

[0057] Test Results

[0058] 1. The resistance, average value and standard deviation data of the resistance measured in Example 1 and Comparative Example 1 are shown in Table 1 below. The average value of the resistance in Example 1 and Comparative Example 1 is plotted as follows: Figure 2 The line chart shown.

[0059] Table 1

[0060]

[0061]

[0062] For the electrode, the increase in the conductive agent content will inevitably enhance the conductivity of the electrode or coating and reduce the resistance. Figure 2The figure shows the relationship between the resistance of the electrode and the coating of five different conductive agent ratios. It can be seen that as the conductive agent ratio increases, the coating resistance gradually decreases; although the electrode resistance also shows the same trend, there is no obvious change when the conductive agent ratio is 2% and 3%, indicating that the coating resistance is more sensitive than the electrode resistance. In addition, as shown in Table 1, the coating resistance test results and standard deviations are much smaller than the electrode resistance test results and standard deviations, indicating that the coating resistance test is not affected by the interface resistance and the test results have good repeatability.

[0063] 2. The resistance, average value and standard deviation data of the resistance measured in Example 2 and Comparative Example 2 are shown in Table 2 below. The average value of the resistance in Example 2 and Comparative Example 2 is plotted as follows: Figure 3 The line chart shown.

[0064] Table 2

[0065]

[0066]

[0067] Figure 3 The figure is the relationship diagram of the resistance of the electrode and the coating under different pressures. It can be seen that with the increase of the test pressure, the electrode resistance shows a phenomenon of first rapid decrease and then slow decrease, and the coating resistance also shows a trend of gradually decreasing, but the difference is small, indicating that the interface resistance between the coating in the electrode and the aluminum foil will decrease with the increase of pressure, while the coating resistance is less affected by the test pressure, and the test results are more stable.

[0068] 3. The resistance, average value and standard deviation data of the resistance measured in Example 3 and Comparative Example 3 are shown in Table 3 below. The average value of the resistance in Example 3 and Comparative Example 3 is plotted as follows: Figure 4 The line chart shown.

[0069] Table 3

[0070]

[0071]

[0072] For the electrode, the increase in slurry thickness will inevitably increase the resistance of the electrode or coating. Figure 4 The figure shows the relationship between the resistance of the electrode and the coating with different slurry thicknesses. It can be seen that as the slurry thickness increases, the coating resistance also gradually increases, and the variation law of the electrode resistance cannot accurately reflect the variation trend of the slurry coating thickness. This shows that the coating resistance test can accurately reflect the variation of the slurry thickness.

[0073] Based on the test results of Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, and Comparative Example 3, it can be seen that the method for measuring the coating resistance in the battery electrode provided by the present invention can significantly distinguish the slight differences between the coatings and is not affected by interface differences. The measurement results are stable, accurate, and reliable.

[0074] It should be noted that although the present invention is disclosed as above by specific embodiments, the above embodiments are not intended to limit the present invention. Ordinary technicians in this field can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope defined in the claims.

Claims

1. A method for accurately measuring the resistance of a pole piece coating, characterized in that: The following steps are involved: S1: Apply the evenly stirred slurry on the insulating film; S2: baking the insulating film coated with the slurry, and then rolling it to obtain an insulating film with a coating; S3: cutting and shaping the insulating film with the coating; S4: using a four-probe probe to measure the coating resistance on the insulating film.

2. The method for accurately measuring the resistance of a pole piece coating according to claim 1, characterized in that: The insulating film is made of polyimide film, polyethylene film, polyvinylidene fluoride, polytetrafluoroethylene or polyethylene terephthalate.

3. The method for accurately measuring the electrode coating resistance according to claim 1, characterized in that: The insulating film is first cleaned with a volatile organic solvent and dried before being coated with the slurry.

4. The method for accurately measuring the electrode coating resistance according to claim 1, characterized in that: In step S2, the baking temperature is 60-120°C.

5. The method for accurately measuring the resistance of a pole piece coating according to claim 1, characterized in that: In step S3, the insulating film with the coating is cut into a rectangle with a length of 6 cm and a width of 2 cm.

6. The method for accurately measuring the resistance of a pole piece coating according to claim 1, characterized in that: In step S4, the cut and shaped insulating film with coating is placed under the four probes, the power of the tester is turned on, and the probes are slowly pressed down. The probes are pressed against the coating and the pressure is controlled by a pressure gauge. After reaching the set pressure, the resistance data is read, which is the coating resistance value.

7. The method for accurately measuring the resistance of a pole piece coating according to claim 6, characterized in that: The pressure of the probe extrusion coating is 5-25MPa.

8. The method for accurately measuring the electrode coating resistance according to claim 1, characterized in that: The mass proportion of the conductive agent in the slurry is 2%-6%.

9. The method for accurately measuring the resistance of a pole piece coating according to claim 1, characterized in that: The thickness of the slurry when applied is 100-400 μm.

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