Pole piece test method

Abstract

The application discloses a kind of pole piece test methods, comprising: pole piece is pretreated, obtains several test samples;Test sample is rolled, and the compaction density of test sample is obtained;The specific surface area of test sample is obtained;The specific surface area of electrode active material is calculated;According to the specific surface area of electrode active material and compaction density, compaction density-specific surface area curve is established;According to the inflection point of compaction density-specific surface area curve, the maximum available compaction density of pole piece is obtained.Through the thickness of several test samples respectively test compaction density, form data curve, avoid the error caused by using thickness average value directly for calculation.By establishing compaction density-specific surface area curve, the maximum available compaction density of pole piece can be more directly and accurately obtained, to ensure that both the discharge capacity of battery can be improved and the infiltration and liquid retention performance of pole piece are not lost.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to an electrode testing method. Background Technology

[0002] Positive and negative electrode sheets are key materials in lithium-ion batteries. During lithium battery manufacturing, the electrode compaction density has a significant impact on electrical performance. Compaction density is closely related to electrode specific capacity, efficiency, internal resistance, and battery cycle performance. A suitable compaction density can increase the battery's discharge capacity, reduce internal resistance, reduce polarization losses, extend battery cycle life, and improve the utilization rate of lithium-ion batteries. Excessive or insufficient compaction is detrimental to battery performance; therefore, finding the optimal compaction density is crucial for battery design.

[0003] In the performance testing of positive and negative electrode sheets, several thickness values ​​are usually measured on the entire electrode sheet, and the average value of all measured values ​​is taken as the thickness of the electrode sheet. However, due to the unevenness of the electrode sheet thickness, the compaction density calculated directly from the average thickness will produce a large error. Alternatively, the compaction density can be determined by testing different compaction-liquid absorption curves. However, this method is greatly affected by ambient temperature and humidity, and is easily interfered with by human factors, resulting in incorrect judgments. Summary of the Invention

[0004] This application provides an electrode testing method, which aims to overcome the error problem caused by external factors in the existing operation of testing the compaction density of positive and negative electrodes of batteries, and to accurately obtain the maximum usable compaction density of the electrode.

[0005] This application provides a method for testing electrode sheets, including the following steps:

[0006] The electrode sheets were pretreated to obtain several test samples;

[0007] The test sample is rolled to obtain the compaction density of the test sample;

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

[0009] The specific surface area S of the electrode active material is calculated according to equation (1). B :

[0010] S B =S A *(a+b) / b Equation (1);

[0011] In equation (1), S Adenoted as , where is the specific surface area of ​​the test sample, 'a' is the surface density of the current collector of the electrode, and 'b' is the surface density of the electrode active material of the electrode.

[0012] A compaction density-specific surface area curve is established based on the specific surface area of ​​the electrode active material and the compaction density.

[0013] The maximum usable compaction density of the electrode is obtained from the inflection point of the compaction density-specific surface area curve.

[0014] In some embodiments, obtaining the compaction density of the test sample includes:

[0015] Measure the thickness of the test sample after it has been rolled;

[0016] The compaction density ρ of the test sample is calculated according to equation (2):

[0017] ρ=(a+b) / h Equation (2);

[0018] In equation (2), h is the thickness of the test sample.

[0019] In some embodiments, the pressure of the roller pressing is 3T to 50T.

[0020] In some embodiments, the areal density α of the current collector in the electrode satisfies: 3 mg / cm³ 2 ≤a≤6mg / cm 2 ;

[0021] The areal density b of the electrode active material of the electrode sheet satisfies: 10 mg / cm³ 2 ≤b≤50mg / cm 2 In some embodiments, the pretreatment of the electrode includes:

[0022] Cut off the tabs and edge wrinkles of the electrode sheet;

[0023] The electrode is cut into 5 to 15 test samples of approximately the same size.

[0024] In some embodiments, establishing a compaction density-specific surface area curve based on the specific surface area of ​​the electrode active material and the compaction density includes:

[0025] The X-axis is set based on the compaction density data of the test sample;

[0026] The Y-axis is set based on the specific surface area data of the electrode active material;

[0027] A rectangular coordinate system is generated, and a compaction density-specific surface area curve is generated in the rectangular coordinate system based on the correspondence between the compaction density value of the test sample and the specific surface area value of the electrode active material.

[0028] In some embodiments, obtaining the maximum usable compaction density of the electrode based on the inflection point of the compaction density-specific surface area curve includes:

[0029] Confirm the inflection point of the compacted density-specific surface area curve;

[0030] Tangents are drawn to the curves on both sides of the inflection point, and the two tangents intersect to form an intersection point;

[0031] In the rectangular coordinate system, confirm the X-axis coordinate of the intersection point to determine the maximum usable compaction density of the electrode.

[0032] In some embodiments, the specific surface area of ​​the test sample is measured by nitrogen adsorption continuous flow method or vacuum static volumetric method.

[0033] 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, and 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。

[0034] In some embodiments, the electrode is a negative electrode, the current collector of the electrode is copper foil, and the electrode active material of the electrode is selected from any one of graphite, soft carbon, and hard carbon.

[0035] The beneficial effect of this application is that it provides a precise method for testing the maximum compaction density of lithium-ion battery material electrodes. The method includes: obtaining electrodes; pre-treating the electrodes to obtain several test samples; rolling the test samples to obtain their compaction density; 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 usable compaction density of the electrode based on the inflection point of the compaction density-specific surface area curve. By calculating the compaction density by testing the thickness of several test samples separately, a data curve is formed, avoiding the errors caused by directly using the average thickness for calculation. The specific surface area data of the electrode can be accurately measured using instruments and equipment; the operation is simple and the results are stable and reliable. By establishing a compaction density-specific surface area curve, the maximum usable compaction density of the electrode can be obtained more intuitively and accurately, effectively avoiding serious consequences such as misjudgments of material performance caused by human error in liquid absorption testing, ensuring that the discharge capacity of the battery is improved without sacrificing the wettability and liquid retention performance of the electrode. Attached Figure Description

[0036] The technical solution and other beneficial effects of this application will become apparent from the following detailed description of specific embodiments in conjunction with the accompanying drawings.

[0037] Figure 1 A schematic flowchart of an electrode testing method provided in an embodiment of this application;

[0038] Figure 2 This is a schematic diagram of the pretreatment process for the electrode sheet provided in an embodiment of this application;

[0039] Figure 3 This is a compaction density-specific surface area curve obtained from tests conducted in an embodiment of this application. Detailed Implementation

[0040] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0041] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for mutual communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. In the description of this application, "multiple" means two or more, unless otherwise expressly and specifically limited. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more features.

[0042] The following disclosure provides many different implementations or examples for carrying out different structures of this application. To simplify the disclosure of this application, the components and arrangements of specific examples are described below. Of course, these are merely examples and are not intended to limit this application.

[0043] This application provides an electrode testing method that calculates compaction density by testing the thickness of several test samples separately, generating a data curve. This avoids the errors caused by directly using the average thickness for calculation. The specific surface area data of the electrode can be accurately measured using instruments and equipment. The operation is simple and the results are stable and reliable. By establishing a compaction density-specific surface area curve, the maximum usable compaction density of the electrode can be obtained more intuitively and accurately. This effectively avoids serious consequences such as misjudgment of material properties caused by human error in liquid absorption testing, ensuring that the discharge capacity of the battery can be improved without compromising the wettability and liquid retention performance of the electrode.

[0044] When the electrode compaction density is too low, the high porosity will cause some particles to fall off during the cycle and form an insulating state, which cannot participate in charging and discharging, resulting in low discharge specific capacity, poor contact between the electrode coating and the current collector, and high contact internal resistance and exchange impedance.

[0045] When the electrode compaction density is too high, the degree of compression between material particles is large, the porosity of the electrode is small, the electrode's ability to absorb electrolyte is poor, the electrolyte is difficult to wet, electronic conduction and ion conduction are not coordinated, dead lithium or lithium plating areas are formed, resulting in low specific capacity of the material, poor electrolyte retention capacity of the battery, large polarization during battery cycling, greater battery decay, significant increase in internal resistance, and poor rate performance and cycle performance.

[0046] Specific surface area refers to the surface area of ​​a unit mass of battery electrode material. It is commonly used to describe the area of ​​microstructures such as particles, pores, and surface cracks in the material, which are closely related to the transport of protons, electrons, and ions in the battery. The larger the specific surface area, the more microstructures are present in the battery electrode, resulting in more contact surface with the electrode reaction, thereby increasing the electrochemical reaction rate and activity of the electrode and improving battery performance.

[0047] Generally, a higher specific surface area can improve battery performance. For example, in batteries, the larger surface area of ​​particles or nanostructures can enhance surface reactivity, increase electrochemical reactions, and improve the battery's energy density and power density. Furthermore, a high specific surface area can also improve electron and ion transport rates, further enhancing battery performance.

[0048] During the initial compaction of the electrode, as the compaction density gradually increases, the air-containing pores in the battery electrode material are gradually compressed, thus reducing the specific surface area. At this stage, the rate of increase in specific surface area is relatively slow. When the compaction density increases to a certain threshold, the pores in the battery electrode are significantly compressed. At this point, an important change occurs in the compaction process: the contact area between electrode material particles increases with increasing compaction density, forming new contact points and further increasing the specific surface area. As the number of contact points gradually increases, the rate of increase in specific surface area increases dramatically, entering a rapid growth phase before eventually approaching saturation. This is because excessively high compaction density can also lead to overly tight contact between particles, slowing the rate of increase in new contact area and thus reducing the rate of increase in specific surface area.

[0049] Therefore, during the compaction process of battery electrodes, there is a stage where the rate of increase in specific surface area suddenly accelerates. By finding the threshold of compaction density corresponding to this stage, the maximum usable compaction density of the battery electrodes can be determined.

[0050] In some embodiments, the testing method for electrodes is as follows: Figure 1 As shown, it includes the following steps:

[0051] S1. Pre-treat the electrode to obtain several test samples.

[0052] The electrode plates are disassembled from the battery cell. The electrode plates can be positive or negative electrode plates, and they include current collectors and electrode active materials.

[0053] 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, and LiNi. x Mn 1-x O2 and LiNix Co y Mn 1-x-y At least one of O2, wherein, 0 <x<1,0<y<1;

[0054] When the electrode is a negative electrode, the current collector is copper foil, and the electrode active material is selected from any one of graphite, soft carbon, and hard carbon.

[0055] like Figure 2 As shown, take the electrode to be tested, cut off the tabs and edge wrinkles of the electrode, and cut it into strip test electrodes with a predetermined length and width to avoid a large difference between the compaction density of the tabs and edge wrinkles and the test results of the flat area in the middle, which would lead to a large error in the final test results.

[0056] Cut the strip test electrode into 5 to 15 test samples of approximately the same size.

[0057] S2. Roll the test sample to obtain the compaction density of the test sample.

[0058] The test samples were rolled with a rolling pressure of 3T to 50T to obtain samples with different rolling thicknesses.

[0059] The compaction density ρ of the test sample is calculated according to equation (2):

[0060] ρ=(a+b) / h……Equation (2);

[0061] In equation (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.

[0062] The surface density 'a' of the current collector satisfies: 3 mg / cm³ 2 ≤a≤6mg / cm 2 It is understandable that the value of 'a' (unit: mg / cm³) can be... 2 The value of 'a' can be any value from 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 range, it can ensure that the electrode sheet has a relatively ideal rolling thickness after rolling.

[0063] The areal density b of the electrode active material satisfies: 10 mg / cm³ 2 ≤b≤50mg / cm 2 It is understandable that the value of b (unit: mg / cm³) 2 The value of b can be any value from 10, 15, 20, 25, 30, 35, 40, 45, 50, or a range between any two values. When the value of b meets the above range, it can ensure that the electrode sheet has a relatively ideal rolling thickness after rolling, thereby obtaining a relatively ideal compaction density.

[0064] S3. Obtain the specific surface area of ​​the test sample.

[0065] The specific surface area S of the electrode active material is calculated according to equation (1). B :

[0066] S B =S A *(a+b) / b……Equation (1);

[0067] In equation (1), S A The specific surface area of ​​the test sample is given by 'a', the surface density of the current collector is given by 'b', and the surface density of the electrode active material is given by 'b'.

[0068] Since the areal densities of the current collector and the electrode active material may differ significantly, directly obtaining the compaction density from the specific surface area of ​​the test sample is prone to large errors. The calculation using Equation (1) can eliminate the interference of the current collector material, and thus compare the specific surface area data of the electrode sheets under different compaction conditions for different materials.

[0069] S4. Establish a compaction density-specific surface area curve based on the specific surface area and compaction density of the electrode active material.

[0070] The X-axis is set based on the compaction density data of the test sample;

[0071] The Y-axis is set based on the specific surface area data of the electrode active material;

[0072] Generate a rectangular coordinate system;

[0073] Based on the correspondence 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.

[0074] S5. Obtain the maximum usable compaction density of the electrode based on the inflection point of the compaction density-specific surface area curve.

[0075] Identify the inflection point of the compacted density-specific surface area curve;

[0076] Draw tangents to the curves on both sides of the inflection point, so that the two tangents intersect to form an intersection point;

[0077] In a rectangular coordinate system, confirm the X-axis coordinate of the intersection point to determine the maximum usable compaction density of the electrode.

[0078] The inflection point in the compaction density-specific surface area curve represents the threshold at which the porosity of the electrode has been significantly compressed and the specific surface area has entered a stage of rapid increase. The intersection of the curves on both sides of the inflection point can be taken as the maximum usable compaction density.

[0079] The testing method for the electrode provided in this application is described below with reference to specific embodiments:

[0080] Example 1

[0081] S1. Pre-treat the negative electrode to obtain several test samples.

[0082] The negative electrode sheet is disassembled from the battery cell. The electrode sheet includes a negative current collector and a negative active material. The negative current collector is copper foil, and the negative active material is artificial graphite.

[0083] Take the electrode to be tested, cut off the tabs and edge wrinkles, and cut it into strip test electrodes with a predetermined length and width. Cut the strip test electrodes into 7 test samples of 4*4mm each.

[0084] S2. Roll the test sample to obtain the compaction density of the test sample.

[0085] The test samples were rolled using an XDG7-5050C roller press, with the rolling pressure set to 5T~45T, to obtain samples with different rolled thicknesses.

[0086] The compaction density ρ of the test sample is calculated according to equation (2):

[0087] ρ=(a+b) / h……Equation (2);

[0088] In equation (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.

[0089] The compaction densities obtained from the tests are shown in Table 1.

[0090] Table 1

[0091]

[0092]

[0093] S3. Obtain the specific surface area of ​​the test sample.

[0094] The specific surface area of ​​the test sample was tested using the Beijing Bestech 3H-2000A. The specific steps are as follows:

[0095] Open the main valve of the mixed gas cylinder, adjust the pressure reducing valve to make the output pressure 0.34 MPa + 0.02 MPa, and turn on the main unit. Take a dry and clean sample tube, weigh it accurately (accurate to 0.0001 g), fill it with the sample, making sure the sample occupies 1 / 2 of the sample tube volume, and clean the sample adhering to the tube wall with a brush. Weigh it again. Place the sample tube into the instrument, attach the heating pack, and perform degassing. Set the degassing temperature to 200℃ and start heating. After reaching the heating temperature, maintain it for 1 hour. After heating, turn off the heating switch, and remove the heating pack after the temperature drops below 100℃. Allow it to cool naturally to room temperature. Remove the sample tube, weigh it accurately (accurate to 0.0001 g), and subtract the weight of the empty sample tube to obtain the net weight of the sample. Place the sample tube back into the instrument, fill the Dewar flask with liquid nitrogen, open the operating software, input the sample mass, and save the test file. After the analysis, analyze the graph and automatically calculate the specific surface area value S. A .

[0096] The specific surface area S of the electrode active material is calculated according to equation (1). B :

[0097] S B =S A *(a+b) / b……Equation (1);

[0098] In equation (1), S A The specific surface area of ​​the test sample is given by 'a', the surface density of the current collector is given by 'b', and the surface density of the electrode active material is given by 'b'.

[0099] S4. Establish a compaction density-specific surface area curve based on the specific surface area and compaction density of the electrode active material, such as... Figure 3 As shown.

[0100] The X-axis is set based on the compaction density data of the test sample;

[0101] The Y-axis is set based on the specific surface area data of the electrode active material;

[0102] Generate a rectangular coordinate system;

[0103] Based on the correspondence 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.

[0104] S5. Obtain the maximum usable compaction density of the electrode based on the inflection point of the compaction density-specific surface area curve.

[0105] Identify the inflection point of the compacted density-specific surface area curve;

[0106] Draw tangents to the curves on both sides of the inflection point, so that the two tangents intersect to form an intersection point;

[0107] In a rectangular coordinate system, confirm the X-axis coordinate of the intersection point to determine the maximum usable compaction density of the electrode.

[0108] The above provides a detailed description of the test method for the maximum usable compaction density of the electrode sheet provided in the embodiments of this application. Specific examples have been used in this application to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions 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 method for testing electrodes, characterized in that, Includes the following steps: The electrode sheets were pretreated to obtain several test samples; The test sample is rolled to obtain the compaction density of the test sample; Obtain the specific surface area of ​​the test sample; The specific surface area of ​​the test sample is tested by either the nitrogen adsorption continuous flow method or the vacuum static volumetric method. The specific surface area S of the active material of the test sample is calculated according to formula (1). B : S B =S A *(a+b) / b Equation (1); In equation (1), S A denoted as , where is the specific surface area of ​​the test sample, 'a' is the surface density of the current collector of the electrode, and 'b' is the surface density of the electrode active material of the electrode. Satisfying: 3mg / cm 2 ≤a≤6mg / cm 2 10mg / cm 2 ≤b≤50mg / cm 2 The interference of the current collector material is eliminated through the calculation of the above formula (1); A compaction density-specific surface area curve is established based on the specific surface area of ​​the electrode active material and the compaction density, and the inflection point of the compaction density-specific surface area curve is identified; the inflection point represents the threshold at which the porosity of the electrode sheet has been compressed and the specific surface area has entered the increasing stage. The maximum usable compaction density of the electrode is obtained from the inflection point of the compaction density-specific surface area curve.

2. The electrode testing method according to claim 1, characterized in that, Obtaining the compaction density of the test sample includes: Measure the thickness of the test sample after it has been rolled; The compaction density ρ of the test sample is calculated according to equation (2): ρ=(a+b) / h (2); In equation (2), h is the thickness of the test sample.

3. The electrode testing method according to claim 1, characterized in that, The pressure of the roller is 3T~50T.

4. The electrode testing method according to claim 1, characterized in that, The pretreatment of the electrode includes: Cut off the tabs and edge wrinkles of the electrode sheet; The electrode is cut into 5 to 15 test samples of approximately the same size.

5. The electrode testing method according to claim 1, characterized in that, Establishing a compaction density-specific surface area curve based on the specific surface area of ​​the electrode active material and the compaction density includes: The X-axis is set based on the compaction density data of the test sample; The Y-axis is set based on the specific surface area 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 based on the correspondence between the compaction density value of the test sample and the specific surface area value of the electrode active material.

6. The electrode testing method according to claim 5, characterized in that, The maximum usable compaction density of the electrode is obtained from the inflection point of the compaction density-specific surface area curve, including: Tangents are drawn to the curves on both sides of the inflection point, and the two tangents intersect to form an intersection point; In the rectangular coordinate system, confirm the X-axis coordinate of the intersection point to determine the maximum usable compaction density of the electrode.

7. The electrode testing method according to claim 1, characterized in that, 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, and 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。 8. The electrode testing method according to claim 1, characterized in that, The electrode is a negative electrode, the current collector of the electrode is copper foil, and the electrode active material of the electrode is selected from any one of graphite, soft carbon, and hard carbon.

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