Pole piece testing method

Abstract

The present application discloses a pole piece testing method. The method comprises: performing pre-processing of pole pieces to obtain a plurality of test samples; performing rolling on a test sample to obtain the compaction density of the test sample; obtaining the specific surface area of the test sample; calculating the specific surface area of an electrode active material; establishing, on the basis of the specific surface area and compaction density of the electrode active material, a compaction density-specific surface area curve; and obtaining, on the basis of an inflection point of the compaction density-specific surface area curve, a maximum available compaction density of the pole piece.

Description

Pole piece test method

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on July 3, 2023, with application number 202310810909.2 and invention name “Pole Testing Method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The embodiments of the present application relate to, but are not limited to, a pole piece testing method. Background Art

[0003] Positive and negative electrodes are key materials in lithium-ion batteries. During the lithium-ion battery manufacturing process, the electrode compaction density has a significant impact on electrical performance. Compaction density is closely related to the electrode specific capacity, efficiency, internal resistance, and battery cycle performance. An appropriate compaction density can increase the battery's discharge capacity, reduce internal resistance, minimize polarization losses, and extend the battery's cycle life. An appropriate electrode compaction density can increase the battery's discharge capacity, reduce internal resistance, minimize polarization losses, extend the battery's cycle life, and improve the utilization rate of lithium-ion batteries. Excessive or insufficient compaction is detrimental to battery performance, so finding the optimal compaction density is crucial for battery design.

[0004] Application Contents

[0005] This application provides a pole piece testing method, comprising the following steps:

[0006] Pre-process the electrode to obtain several test samples;

[0007] Rolling the test sample to obtain a compaction density of the test sample;

[0008] Obtaining the specific surface area of ​​the test sample;

[0009] The specific surface area S of the electrode active material is calculated according to formula (1): B : S B =S A *(a+b) / b formula (1);

[0010] In formula (1), S A is the specific surface area of ​​the test sample, a is the surface density of the current collector of the electrode piece, and b is the surface density of the electrode active material of the electrode piece;

[0011] establishing a compaction density-specific surface area curve according to the specific surface area of ​​the electrode active material and the compaction density;

[0012] The maximum available compaction density of the pole piece is obtained according to the inflection point of the compaction density-specific surface area curve.

[0013] In some embodiments, obtaining the compacted density of the test sample comprises:

[0014] Measuring the thickness of the rolled test sample;

[0015] The compacted density ρ of the test sample is calculated according to formula (2): ρ = (a + b) / h Formula (2);

[0016] In formula (2), h is the thickness of the test sample.

[0017] In some embodiments, the roller pressing pressure is 3T to 50T.

[0018] In some embodiments, the surface density a of the current collector of the pole piece satisfies: 3 mg / cm 2 ≤a≤6mg / cm 2 ;

[0019] The surface density b of the electrode active material of the electrode sheet satisfies: 10 mg / cm 2 ≤b≤50mg / cm 2 In some embodiments, the pre-processing of the electrode includes:

[0020] Cutting off the pole ears and edge wrinkles of the pole piece;

[0021] The electrode is cut into 5 to 15 test samples of similar size.

[0022] In some embodiments, establishing a compaction density-specific surface area curve according to the specific surface area and the compaction density of the electrode active material comprises:

[0023] Setting the X-axis according to the compacted density value data of the test sample;

[0024] Setting the Y axis according to the specific surface area value data of the electrode active material;

[0025] A rectangular coordinate system is generated, and a compaction density-specific surface area curve is generated in the rectangular coordinate system according to the corresponding relationship between the compaction density value of the test sample and the specific surface area value of the electrode active material.

[0026] In some embodiments, obtaining the maximum available compaction density of the pole piece according to the inflection point of the compaction density-specific surface area curve includes:

[0027] Identifying the inflection point of the compacted density-specific surface area curve;

[0028] Draw tangent lines on the curves on both sides of the inflection point, respectively, so that the two tangent lines intersect to form an intersection point;

[0029] The X-axis coordinate of the intersection point is confirmed in the rectangular coordinate system to determine the maximum available compaction density of the pole piece.

[0030] In some embodiments, the specific surface area of ​​the sample is measured by a nitrogen adsorption continuous flow method or a vacuum static volumetric method.

[0031] In some embodiments, the electrode is a positive electrode, the current collector of the electrode is aluminum foil, and the electrode active material of the electrode is selected from LiMnO2, LiMn2O4, LiCoO2, LiFePO4, LiNi x Mn 1-x O2 and LiNi x Co y Mn 1-x-y At least one of O2; wherein, 0 <x<1,0<y<1。

[0032] In some embodiments, the electrode sheet is a negative electrode sheet, the current collector of the electrode sheet is copper foil, and the electrode active material of the electrode sheet is selected from any one of graphite, soft carbon and hard carbon. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The following detailed description of the specific implementation methods of the present application in conjunction with the accompanying drawings will demonstrate the technical solutions and other beneficial effects of the present application.

[0034] FIG1 is a schematic flow chart of a pole piece testing method provided in an embodiment of the present application;

[0035] FIG2 is a schematic diagram of a process for pre-processing a pole piece according to an embodiment of the present application;

[0036] FIG3 is a compaction density-specific surface area curve obtained by testing in the examples of the present application. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0038] In the existing related technologies, in the performance test of positive and negative electrode sheets, several thickness values ​​are generally measured on an entire electrode, and the average value of all measured values ​​is used as the thickness of the electrode sheet. Due to the uneven thickness of the electrode sheet, the compaction density directly calculated by the average value of the thickness will produce a large error; or the compaction density is determined by testing different compaction-liquid absorption curves, but this method is greatly affected by ambient temperature and humidity, and is easily interfered by human factors, resulting in wrong judgments.

[0039] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the components and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application.

[0040] The present embodiment provides a pole piece testing method that calculates the compacted density by measuring the thickness of several test samples and forming a data curve, thus avoiding the errors caused by directly using the average thickness for calculation. The specific surface area data of the pole piece can be accurately measured using instruments and equipment, which is simple to operate and produces stable and reliable results. By establishing a compacted density-specific surface area curve, the maximum available compacted density of the pole piece can be obtained more intuitively and accurately, effectively avoiding the serious consequences of misjudging material properties caused by human factors such as test liquid absorption errors, and ensuring that the battery discharge capacity can be improved without compromising the wettability and liquid retention performance of the pole piece.

[0041] When the electrode compaction density is too small, the higher porosity will cause some particles to fall off during the cycle and form an insulating state, which makes them unable to participate in charging and discharging, resulting in low discharge specific capacity, poor contact between the electrode coating and the current collector, and large contact internal resistance and exchange impedance.

[0042] When the compaction density of the electrode is too large, the degree of extrusion between the material particles is large, the porosity of the electrode is small, the ability of the electrode to absorb electrolyte is poor, the electrolyte is difficult to infiltrate, the electronic conduction and ion conduction are not coordinated, and dead lithium or lithium precipitation areas are formed, resulting in a low specific capacity of the material and poor liquid retention capacity of the battery. The greater the polarization during the battery cycle, the greater the attenuation will be, the internal resistance will increase significantly, and the rate performance and cycle performance will be poor.

[0043] Specific surface area refers to the surface area per unit mass of a battery electrode material. It is typically used to describe the area of ​​microscopic structures within the material, such as particles, pores, and surface cracks. These structures are closely related to the transport of protons, electrons, and ions in the battery. A larger specific surface area indicates a greater number of microstructures within the battery electrode, providing more contact surface for electrode reactions, thereby increasing the electrochemical reaction rate and activity of the electrode, and thus improving battery performance.

[0044] Generally speaking, a higher specific surface area improves battery performance. For example, in batteries, particles or nanostructures with a larger surface area can increase surface reactivity, enhance electrochemical reactions, and increase the battery's energy and power density. Furthermore, a high specific surface area can increase the rate of electron and ion transport, further enhancing battery performance.

[0045] During the initial compaction process of the electrode, as the compaction density gradually increases, the air-containing pores in the battery electrode material are gradually compressed. Therefore, the compressed pores will gradually reduce the specific surface area. During this stage, the rate of increase of the specific surface area will be slow. When the compaction density increases to a certain threshold, the pores in the battery electrode have been significantly compressed. At this time, an important change will occur in the compaction process: the contact area between the electrode material particles will increase with the increase in compaction density, and new contact points will be formed, thereby increasing the specific surface area. As the number of contact points gradually increases, the rate of increase of the specific surface area will increase sharply, entering a stage of rapid growth, and eventually gradually approaching saturation. This is because excessively high compaction density will also cause the contact between particles to become too close, and the rate of increase of new contact area will slow down, resulting in a decrease in the rate of growth of the specific surface area.

[0046] Therefore, during the compaction process of the battery electrode, there is a stage where the growth rate of the specific surface area suddenly becomes faster. By finding the threshold value of the compaction density corresponding to this stage, the maximum available compaction density of the battery electrode can be determined.

[0047] In some embodiments, the electrode testing method is shown in FIG1 and includes the following steps:

[0048] S1. Pre-process the electrode to obtain several test samples.

[0049] The electrode sheet is disassembled from the battery cell. The electrode sheet can be a positive electrode sheet or a negative electrode sheet. The electrode sheet includes a current collector and an electrode active material.

[0050] Among them, when the electrode is a positive electrode, the current collector is aluminum foil, and the electrode active material is selected from LiMnO2, LiMn2O4, LiCoO2, LiFePO4, LiNi x Mn 1-x O2 and LiNi x Co y Mn 1-x-y At least one of O2, wherein 0 <x<1,0<y<1;

[0051] When the electrode sheet is a negative electrode sheet, the current collector is copper foil, and the electrode active material is selected from any one of graphite, soft carbon and hard carbon.

[0052] As shown in Figure 2, take the electrode to be tested, cut off the electrode ears and edge wrinkles of the electrode, and cut it into strip test electrode sheets with a predetermined length and width to avoid a large difference between the compaction density of the electrode ears and edge wrinkles and the test results of the middle flat area, which will lead to a large error in the final test results.

[0053] Cut the strip test electrode into 5 to 15 test samples of similar size.

[0054] S2. Roll the test sample to obtain the compaction density of the test sample.

[0055] The test samples were rolled at a pressure of 3T to 50T to obtain samples with different rolling thicknesses;

[0056] The compacted density ρ of the test sample is calculated according to formula (2): ρ=(a+b) / h……Formula (2);

[0057] In formula (2), h is the thickness of the test sample, a is the surface density of the current collector, and b is the surface density of the electrode active material.

[0058] The surface density a of the current collector satisfies: 3 mg / cm 2 ≤a≤6mg / cm 2 It is understandable that the value of a (unit: mg / cm 2 ) can be any value among 3, 3.5, 4, 4.5, 5, 5.5, 6 or a range between any two values. When the value of a satisfies the above value range, it can ensure that the electrode has a relatively ideal rolling thickness after rolling.

[0059] The surface density b of the electrode active material satisfies: 10 mg / cm 2 ≤b≤50mg / cm 2 It is understandable that the value of b (unit: mg / cm 2 ) can be any value among 10, 15, 20, 25, 30, 35, 40, 45, 50, or a range between any two values. When the value of b satisfies the above value range, it can ensure that the electrode has a relatively ideal rolling thickness after rolling, thereby obtaining a relatively ideal compaction density.

[0060] S3. Obtain the specific surface area of ​​the test sample.

[0061] The specific surface area S of the electrode active material is calculated according to formula (1): B : S B =S A *(a+b) / b……Formula (1);

[0062] In formula (1), S Ais the specific surface area of ​​the test sample, a is the surface density of the current collector, and b is the surface density of the electrode active material.

[0063] Since the surface density of the current collector and the electrode active material may differ significantly, obtaining the compaction density directly by measuring the specific surface area of ​​the sample is prone to large errors. The calculation using formula (1) can eliminate the interference of the current collector material and further compare the specific surface area data of the electrode sheets under different materials and different compactions.

[0064] S4. Establish a compaction density-specific surface area curve based on the specific surface area and compaction density of the electrode active material.

[0065] Set the X-axis according to the compacted density value data of the test sample;

[0066] The Y axis is set according to the specific surface area value data of the electrode active material;

[0067] Generate a rectangular coordinate system;

[0068] According to the corresponding relationship between the compaction density value of the test sample and the specific surface area value of the electrode active material, a compaction density-specific surface area curve is generated in a rectangular coordinate system.

[0069] S5. Obtain the maximum available compaction density of the electrode according to the inflection point of the compaction density-specific surface area curve.

[0070] Identify the inflection point of the compacted density-specific surface area curve;

[0071] Draw tangent lines on the curves on both sides of the inflection point so that the two tangent lines intersect to form an intersection point;

[0072] Confirm the X-axis coordinate of the intersection point in the rectangular coordinate system and determine the maximum available compaction density of the pole piece.

[0073] The inflection point in the compaction density-specific surface area curve indicates the threshold value at which the porosity in the electrode has been significantly compressed and the specific surface area enters a rapid increase stage. Tangents are drawn on the curves on both sides of the inflection point, and the intersection formed can be used as the maximum available compaction density.

[0074] The following is an explanation of the electrode testing method provided in this application in conjunction with specific embodiments:

[0075] Example 1

[0076] S1. Pre-treat the negative electrode to obtain several test samples.

[0077] Disassemble the negative electrode sheet from the battery cell. The sheet includes the negative electrode current collector and the negative electrode active material. The negative electrode current collector is copper foil, and the negative electrode active material is artificial graphite.

[0078] Take the electrode to be tested, cut off the electrode ears and edge wrinkles of the electrode, cut it into strip test electrode pieces with a predetermined length and width, and cut the strip test electrode pieces into 7 4*4mm test samples.

[0079] S2. Roll the test sample to obtain the compaction density of the test sample.

[0080] The test samples were rolled using a roller press XDG7-5050C, with the rolling pressure set at 5T to 45T to obtain samples with different rolling thicknesses.

[0081] The compacted density ρ of the test sample is calculated according to formula (2): ρ=(a+b) / h……Formula (2);

[0082] In formula (2), h is the thickness of the test sample, a is the surface density of the current collector, and b is the surface density of the electrode active material.

[0083] The compacted density obtained from the test is shown in Table 1.

[0084] Table 1

[0085] S3. Obtain the specific surface area of ​​the test sample.

[0086] The specific surface area of ​​the test sample was tested using Beijing Best 3H-2000A. The specific steps are as follows:

[0087] Open the main valve of the mixed gas cylinder, adjust the pressure reducing valve so that the output pressure is 0.34Mpa+0.02Mpa, and turn on the main unit; take a dry and clean sample tube, accurately weigh its mass (accurate to 0.0001g), load the sample, the sample occupies 1 / 2 of the volume of the sample tube, brush off the sample on the tube wall with a brush, and weigh the mass; load the sample tube into the instrument, put on the heating bag, perform the degassing operation, set the degassing temperature to 200℃, and start heating. After reaching the heating temperature, maintain it for 1 hour; after heating is completed, turn off the heating switch, remove the heating bag after the temperature drops below 100℃, cool it naturally to room temperature, remove the sample tube, accurately weigh its weight (accurate to 0.0001g), subtract the weight of the empty sample tube, and obtain the net weight of the sample; after the sample tube is installed on the instrument, fill the Dewar flask with liquid nitrogen, open the operating software, enter the sample mass, and save the test file; after the analysis is completed, analyze the graph and automatically calculate the specific surface area value S A .

[0088] The specific surface area S of the electrode active material is calculated according to formula (1): B : S B =S A *(a+b) / b……Formula (1);

[0089] In formula (1), SA is the specific surface area of ​​the test sample, a is the surface density of the current collector, and b is the surface density of the electrode active material.

[0090] S4. Establish a compaction density-specific surface area curve based on the specific surface area and compaction density of the electrode active material, as shown in FIG3 .

[0091] Set the X-axis according to the compacted density value data of the test sample;

[0092] The Y axis is set according to the specific surface area value data of the electrode active material;

[0093] Generate a rectangular coordinate system;

[0094] According to the corresponding relationship between the compaction density value of the test sample and the specific surface area value of the electrode active material, a compaction density-specific surface area curve is generated in a rectangular coordinate system.

[0095] S5. Obtain the maximum available compaction density of the electrode according to the inflection point of the compaction density-specific surface area curve.

[0096] Identify the inflection point of the compacted density-specific surface area curve;

[0097] Draw tangent lines on the curves on both sides of the inflection point so that the two tangent lines intersect to form an intersection point;

[0098] Confirm the X-axis coordinate of the intersection point in the rectangular coordinate system and determine the maximum available compaction density of the pole piece.

[0099] The beneficial effect of the present application is that it provides a precise test method for the maximum compaction density of lithium-ion battery material pole pieces, the test method comprising: obtaining pole pieces; pre-treating the pole pieces to obtain a number of test samples; rolling the test samples to obtain the compaction density of the test samples; obtaining the specific surface area of ​​the test samples; calculating the specific surface area of ​​the electrode active material based on the specific surface area of ​​the test samples; establishing a compaction density-specific surface area curve, and obtaining the maximum available compaction density of the pole piece based on the inflection point of the compaction density-specific surface area curve. By measuring the thickness of a number of test samples and calculating the compaction density, a data curve is formed, which avoids the error caused by directly using the average thickness for calculation. The specific surface area data of the pole piece can be accurately measured using instruments and equipment, the operation is simple, and the results are stable and reliable. By establishing the compaction density-specific surface area curve, the maximum available compaction density of the pole piece can be obtained more intuitively and accurately, effectively avoiding the serious consequences of misjudgment of material performance caused by human factors in testing liquid absorption errors, and ensuring that the discharge capacity of the battery can be improved without losing the wettability and liquid retention performance of the pole piece.

[0100] The above is a detailed introduction to the test method for the maximum available compaction density of the pole piece provided in the embodiments of this application. Specific examples are used in this application to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the technical solutions and core ideas of this application; ordinary technicians in this field should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A pole piece testing method, comprising the following steps: Pre-process the pole piece to obtain several test samples; Rolling the test sample to obtain a compaction density of the test sample; Obtaining the specific surface area of ​​the test sample; The specific surface area S of the electrode active material is calculated according to formula (1): B : S B =S A *(a+b) / b Formula (1); In formula (1), S A is the specific surface area of ​​the test sample, a is the surface density of the current collector of the pole piece, and b is the surface density of the electrode active material of the pole piece; Establishing a compaction density-specific surface area curve according to the specific surface area of ​​the electrode active material and the compaction density; The maximum available compaction density of the pole piece is obtained according to the inflection point of the compaction density-specific surface area curve.

2. A pole piece testing method according to claim 1, wherein: Obtaining the compacted density of the test sample comprises: Measuring the thickness of the rolled test sample; The compacted density ρ of the test sample is calculated according to formula (2): ρ=(a+b) / h Formula (2); In formula (2), h is the thickness of the test sample.

3. A pole piece testing method according to claim 1, wherein: The roller pressing pressure is 3T to 50T.

4. A pole piece testing method according to claim 1, wherein: The surface density a of the current collector of the pole piece satisfies: 3 mg / cm 2 ≤a≤6mg / cm 2 .

5. A pole piece testing method according to claim 1 or 4, wherein: The surface density b of the electrode active material of the electrode sheet satisfies: 10 mg / cm 2 ≤b≤50mg / cm 2 .

6. A pole piece testing method according to claim 1, wherein: Pre-processing the pole piece includes: Cutting off the pole ears and edge wrinkles of the pole piece; The pole piece is cut into 5 to 15 test samples of similar size.

7. A pole piece testing method according to claim 1, wherein: Establishing a compaction density-specific surface area curve according to the specific surface area of ​​the electrode active material and the compaction density comprises: Setting the X-axis according to the compacted density value data of the test sample; Setting the Y axis according to the specific surface area value data of the electrode active material; A rectangular coordinate system is generated, and a compaction density-specific surface area curve is generated in the rectangular coordinate system according to the corresponding relationship between the compaction density value of the test sample and the specific surface area value of the electrode active material.

8. A pole piece testing method according to claim 7, wherein: Obtaining the maximum available compaction density of the pole piece according to the inflection point of the compaction density-specific surface area curve includes: confirming the inflection point of the compacted density-specific surface area curve; Draw tangent lines for the curves on both sides of the inflection point respectively, so that the two tangent lines intersect to form an intersection point; The X-axis coordinate of the intersection point is determined in the rectangular coordinate system to determine the maximum available compaction density of the pole piece.

9. A pole piece testing method according to claim 1, wherein: The specific surface area of ​​the test sample is tested by a nitrogen adsorption continuous flow method or a vacuum static volume method.

10. A pole piece testing method according to claim 1, wherein: When the electrode is a positive electrode, the current collector of the electrode is aluminum foil, and the electrode active material of the electrode is selected from LiMnO2, LiMn2O4, LiCoO2, LiFePO4, LiNi x Mn 1-x O2 and LiNi x Co y Mn 1-x-y At least one of O2; wherein 0 <x<1,0<y<1; When the electrode sheet is a negative electrode sheet, the current collector of the electrode sheet is copper foil, and the electrode active material of the electrode sheet is selected from any one of graphite, soft carbon and hard carbon.

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