Method for determining the amount of conductive agent in each layer of a multi-layer coated pole piece and application thereof

Abstract

This application relates to a method and application for determining the amount of conductive agent in each layer of a multilayer coated electrode. The method includes the following steps: determining the optimal amount of conductive agent in a single-layer coated electrode with m different areal densities, wherein the single-layer coated electrode includes a single active material layer; based on the optimal amount of conductive agent in the single-layer coated electrode with different areal densities, constructing a fitting curve between the optimal amount of conductive agent in the single-layer coated electrode and the areal density of the single-layer coated electrode, obtaining a functional relationship with areal density as the independent variable G and conductive agent amount as the dependent variable B; for each active material layer in the multilayer coated electrode, the sum of the areal densities of the active material layer and all active material layers located on the surface of the active material layer away from the current collector is used as the independent variable G in the functional relationship, and the obtained dependent variable B is used as the amount of conductive agent in the active material layer. This achieves precise quantification of the amount of conductive agent in each layer of the multilayer coated electrode.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method for determining the amount of conductive agent in each layer of a multilayer coated electrode and its application. Background Technology

[0002] With the large-scale application of rechargeable batteries in electric vehicles, energy storage systems, and consumer electronics, improving their energy density and power density has become a popular research direction. When using the same type of active materials, current technologies typically increase the energy density of the battery by increasing the coating weight (area density) of the active material layer. However, increasing the coating weight inevitably leads to an increase in the battery's internal resistance, which may result in a series of problems such as battery capacity decay, increased heat generation, decreased output voltage, decreased power output, reduced charging efficiency, and even thermal runaway.

[0003] Currently, the multi-layer coating process can effectively solve the above problems. The multi-layer coated electrode includes a current collector and multiple active material layers stacked sequentially on the current collector. Through the flexible design and combination of multiple active material layers, it is easy to balance the energy density and safety of the battery.

[0004] However, there is currently no clear solution in the industry for determining the amount of conductive agent in each active material layer of multilayer coated electrodes during the production process. Currently, the industry mostly relies on experience to determine the amount of conductive agent in each active material layer of multilayer coated electrodes, resulting in significant trial-and-error costs. Summary of the Invention

[0005] In view of this, the present application provides a method and application for determining the amount of conductive agent in each layer of a multilayer coated electrode to solve at least one problem existing in the background art.

[0006] In a first aspect, embodiments of this application provide a method for determining the amount of conductive agent in each layer of a multilayer coated electrode, characterized in that the multilayer coated electrode includes a current collector and multiple active material layers sequentially stacked on at least one surface of the current collector; the method includes the following steps:

[0007] S1: Determine the optimal amount of conductive agent in m single-layer coated electrodes with different areal densities, wherein the single-layer coated electrode comprises a single-layer active material layer; for each of the single-layer coated electrodes, the method for determining the optimal amount includes:

[0008] Prepare n single-layer coated electrodes with equal areal density but different amounts of conductive agent. Fabricate each of the single-layer coated electrodes into a battery and test the internal resistance of the battery. Using the amount of conductive agent of the single-layer coated electrode as the independent variable x and the internal resistance of the corresponding battery as the dependent variable y, fit the curve to obtain a fitting curve. The minimum x value corresponding to the absolute value of the slope of the fitting curve reaching the preset slope value is determined as the optimal amount of conductive agent in the single-layer coated electrode.

[0009] S2: Based on the optimal amount of conductive agent in monolayer coated electrodes under different areal densities, a fitting curve between the optimal amount of conductive agent in monolayer coated electrodes and the areal density of monolayer coated electrodes is constructed, and a functional relationship is obtained with areal density as independent variable G and conductive agent amount as dependent variable B.

[0010] S3: For each active material layer in the multilayer coated electrode, the sum of the surface density of the active material layer and all active material layers on the surface of the active material layer away from the current collector is taken as the independent variable G in the functional relationship, and the resulting dependent variable B is taken as the amount of conductive agent in the active material layer.

[0011] In conjunction with the first aspect of this application, in an alternative embodiment, in step S1, m ≥ 3.

[0012] In conjunction with the first aspect of this application, in an optional embodiment, in step S1, the preset slope value is less than or equal to 5% of the maximum absolute value of the slope of the fitted curve, preferably 0.

[0013] In conjunction with the first aspect of this application, in an optional embodiment, step S1 involves fabricating n monolayer coated electrodes with equal areal density but different amounts of conductive agent, including:

[0014] The amount of conductive agent in the n single-layer coated electrodes to be tested is increased sequentially from a first preset value to a second preset value; wherein, the single increase in the amount of conductive agent is less than or equal to 33% of the difference between the second preset value and the first preset value.

[0015] In conjunction with the first aspect of this application, in an optional embodiment, the single increment value is less than or equal to 20% of the difference between the second preset value and the first preset value, preferably 10%.

[0016] In conjunction with the first aspect of this application, in an alternative embodiment, the single increment value is a fixed value.

[0017] In conjunction with the first aspect of this application, in an optional embodiment, the amount of conductive agent in the monolayer coated electrode is the mass percentage of the conductive agent in the monolayer active material layer; the first preset value is less than or equal to 0.3%, preferably 0%; the second preset value is greater than or equal to 3%, preferably greater than or equal to 5%.

[0018] In conjunction with the first aspect of this application, in an optional embodiment, after step S2, a step of detecting the accuracy of the functional relationship is further included:

[0019] S21. Based on the functional relationship, the amount of the first conductive agent at a certain surface density is obtained, and the first test single-layer coated electrode is prepared.

[0020] Keeping the areal density constant, reduce the amount of conductive agent based on the amount of the first conductive agent to produce a second test single-layer coated electrode sheet; keep the areal density constant, increase the amount of conductive agent based on the amount of the first conductive agent to produce a third test single-layer coated electrode sheet.

[0021] The absolute values ​​of the differences between the amount of conductive agent in the second and third test single-layer coated electrode sheets and the amount of the first conductive agent are both less than the minimum difference in the amount of conductive agent in different test single-layer coated electrode sheets in step S1.

[0022] S22. The first test single-layer coated electrode, the second test single-layer coated electrode, and the third test single-layer coated electrode are respectively made into a first battery, a second battery, and a third battery, and the internal resistance of each battery is tested.

[0023] S23. Determine whether the first internal resistance of the first battery, the second internal resistance of the second battery, and the third internal resistance of the third battery satisfy the following conditions: the second internal resistance is greater than the first internal resistance and the relative difference between the second internal resistance and the first internal resistance is greater than or equal to a first preset difference, and the relative difference between the third internal resistance and the first internal resistance is less than or equal to a second preset difference, and the first preset difference is greater than the second preset difference.

[0024] If the above conditions are met, proceed to step S3;

[0025] If the above conditions are not met, increase the value of m in step S1, and re-obtain the functional relationship according to steps S1 and S2.

[0026] In conjunction with the first aspect of this application, in an optional embodiment, the second preset difference is less than or equal to 5%.

[0027] Secondly, embodiments of this application provide the application of the method for determining the amount of conductive agent in each layer of a multilayer coated electrode as described in any of the first aspects in the preparation of the electrode; optionally, the electrode includes a positive electrode and / or a negative electrode.

[0028] Compared with the prior art, the embodiments of this application have the following beneficial effects:

[0029] The present application provides a method and application for determining the amount of conductive agent in each layer of a multilayer coated electrode. The multilayer coated electrode includes a current collector and multiple active material layers sequentially stacked on at least one side surface of the current collector. In the method for determining the amount of conductive agent in each layer of the multilayer coated electrode, the optimal amount of conductive agent in a single-layer coated electrode with m different areal densities is first determined. Then, based on the optimal amount of conductive agent in a single-layer coated electrode with different areal densities, a functional relationship can be obtained with areal density as the independent variable G and the amount of conductive agent as the dependent variable B. Next, for each active material layer in the multilayer coated electrode, the sum of the areal densities of the active material layer and all active material layers on the surface of the active material layer away from the current collector is used as the independent variable G in the functional relationship, and the resulting dependent variable B is the amount of conductive agent in the active material layer. This application embodiment achieves precise quantification of the amount of conductive agent in each layer of a multilayer coated electrode. The method is simple, practical, and feasible, filling the gap in determining the amount of conductive agent in each layer of a multilayer coated electrode. In addition, this application embodiment also considers that the active material layer closer to the current collector theoretically has a larger maximum charge capacity. Therefore, by using the sum of the areal densities of the active material layer and all active material layers on the surface of the active material layer away from the current collector as the independent variable G in the functional relationship, and using the obtained dependent variable B as the amount of conductive agent in the active material layer, the amount of conductive agent in each active material layer gradually decreases from the active material layer closer to the current collector to the active material layer farther away from the current collector. This helps to improve the energy density of the battery while maintaining a low battery internal resistance.

[0030] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0031] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0032] Figure 1 A flowchart illustrating a method for determining the amount of conductive agent in each layer of a multilayer coated electrode, provided in an embodiment of this application;

[0033] Figure 2A flowchart illustrating another method for determining the amount of conductive agent in each layer of a multilayer coated electrode, provided in an embodiment of this application;

[0034] Figure 3 A cross-sectional structural diagram of a multilayer coated electrode sheet provided for an embodiment of this application;

[0035] Figure 4 This is a fitting curve between the optimal amount of conductive agent in a single-layer coated electrode and the areal density of the single-layer coated electrode, based on the optimal amount of conductive agent in the single-layer coated electrode under different areal densities in the embodiments of this application. Detailed Implementation

[0036] To make the technical solution and beneficial effects of the present invention more apparent and understandable, a detailed description is provided below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional experimental conditions. Unless otherwise specified, all reagents and raw materials used in this invention are commercially available.

[0037] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and steps described in detail.

[0038] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0039] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.

[0040] Unless otherwise defined, the technical and scientific terms used in this application have the same meanings as those in the technical and scientific field to which this application pertains.

[0041] Unless otherwise specified, the techniques or conditions described in the following embodiments are generally performed in accordance with conventional techniques or conditions described in the literature in this field, or in accordance with the product manual and the manufacturer's recommendations. All numerical ranges in the following embodiments include endpoint values.

[0042] This application provides a method for determining the amount of conductive agent in each layer of a multilayer coated electrode. The multilayer coated electrode includes a current collector and multiple active material layers sequentially stacked on at least one surface of the current collector; please refer to... Figure 1 The method for determining the amount of conductive agent in each layer of the multilayer coated electrode provided in this application includes the following steps:

[0043] S1: Determine the optimal amount of conductive agent in m single-layer coated electrodes with different areal densities, where each single-layer coated electrode consists of a single layer of active material. The methods for determining the optimal amount for each single-layer coated electrode include:

[0044] Prepare n single-layer coated electrodes with equal areal density but different amounts of conductive agent. Fabricate each single-layer coated electrode into a battery and test the internal resistance of the battery. Use the amount of conductive agent in the single-layer coated electrode as the independent variable x and the internal resistance of the corresponding battery as the dependent variable y. Fit the curve to obtain the fitting curve. Determine the minimum x value corresponding to the absolute value of the slope of the fitting curve reaching the preset slope value as the optimal amount of conductive agent in the single-layer coated electrode.

[0045] S2: Based on the optimal amount of conductive agent in monolayer coated electrodes under different areal densities, a fitting curve between the optimal amount of conductive agent in monolayer coated electrodes and the areal density of monolayer coated electrodes is constructed, and a functional relationship is obtained with areal density as independent variable G and conductive agent amount as dependent variable B.

[0046] S3: For each active material layer in a multilayer coated electrode, the sum of the surface densities of the active material layer and all active material layers on the surface of the active material layer away from the current collector is taken as the independent variable G in the functional relationship, and the resulting dependent variable B is taken as the amount of conductive agent in the active material layer.

[0047] This application embodiment achieves precise quantification of the amount of conductive agent in each layer of a multilayer coated electrode. The method is simple, practical, and feasible, filling the gap in determining the amount of conductive agent in each layer of a multilayer coated electrode. In addition, this application embodiment also considers that the active material layer closer to the current collector theoretically has a larger maximum charge capacity. Therefore, by using the sum of the areal densities of the active material layer and all active material layers on the surface of the active material layer away from the current collector as the independent variable G in the functional relationship, and using the obtained dependent variable B as the amount of conductive agent in the active material layer, the amount of conductive agent in each active material layer gradually decreases from the active material layer closer to the current collector to the active material layer farther away from the current collector. This helps to improve the energy density of the battery while maintaining a low battery internal resistance.

[0048] In step S1, fabricating n single-layer coated electrodes with equal areal density but different amounts of conductive agent may include: sequentially increasing the amount of conductive agent in the n single-layer coated electrodes from a first preset value to a second preset value; wherein, the single increase in the amount of conductive agent is less than or equal to 33% of the difference between the second preset value and the first preset value.

[0049] Specifically, the amount of conductive agent in a single-layer coated electrode can be considered as the mass percentage of the conductive agent in the single-layer active material layer. The active material layer in the single-layer coated electrode to be tested includes an active material (also known as the main material), a conductive agent, and other additives (specifically, including binders). The mass percentages of the main material, conductive agent, and other additives in the active material layer are represented by A%, B%, and C%, respectively, where A+B+C=100. From the first single-layer coated electrode to be tested to the nth single-layer coated electrode, the amount of conductive agent B% increases sequentially from a first preset value B0% to a second preset value B0%. n The percentage of other additives (C%) remains constant, while the percentage of main material (A%) is adjusted accordingly. For example, if the amount of conductive agent increases, the amount of main material decreases accordingly to maintain A+B+C=100, ensuring that the areal density of the n tested single-layer coated electrodes is equal. For example, the conductive agent may include at least one of conductive carbon black, carbon fiber, graphene, and carbon nanotubes. The active material includes a positive electrode active material or a negative electrode active material, wherein the positive electrode active material includes at least one of ternary positive electrode materials, lithium iron phosphate materials, lithium cobalt oxide, and lithium nickel oxide, and the negative electrode active material includes, for example, graphite and / or silicon-based materials. Other additives may include at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid.

[0050] In this embodiment, from the first monolayer coated electrode to the nth electrode, the amount of conductive agent B% increases sequentially from a first preset value B0% to a second preset value B0%. nThe single increase in the amount of conductive agent is less than or equal to 33% of the difference between the second preset value and the first preset value. This ensures that at least three conductive agent dosage points can be set between the first preset value and the second preset value, so that n is greater than or equal to 5. This helps to improve the accuracy of the optimal amount of conductive agent in the subsequently obtained single-layer coated electrode.

[0051] Furthermore, in some specific embodiments, from the first monolayer coated electrode to the nth monolayer coated electrode, the single increase in the amount of conductive agent can be less than or equal to 20% of the difference between the second preset value and the first preset value, preferably 15%, and more preferably 10%. This increases the value of n, which further increases the gradient of conductive agent amount, thereby helping to further improve the accuracy of the optimal amount of conductive agent in the subsequently obtained monolayer coated electrodes.

[0052] In some specific embodiments, the increment value can be a fixed value. This increases the uniformity of the conductive agent dosage variation in the n tested monolayer coated electrodes, thereby improving the accuracy of the optimal conductive agent dosage in the subsequently obtained monolayer coated electrodes.

[0053] The first and second preset values ​​can be adjusted according to the type of single-layer coated electrode. For single-layer coated electrodes with low areal density (also known as thin-coated electrodes), the appropriate amount of conductive agent is usually relatively small, in which case the first preset value needs to be small enough; while for single-layer coated electrodes with high areal density (also known as thick-coated electrodes), the appropriate amount of conductive agent is usually relatively large, in which case the second preset value needs to be large enough. This is beneficial for obtaining the optimal amount of conductive agent in the accurate single-layer coated electrode.

[0054] In some embodiments, the first preset value B0% may be less than or equal to 0.3%, preferably 0%; the second preset value B n The percentage can be greater than or equal to 3%, preferably greater than or equal to 5%. This can accommodate the needs of both thin-coated and thick-coated electrodes, thus broadening its applicability. Specifically, the first preset value B0% can be 0%, and the second preset value B... n % can be 5%; or, the first preset value B0% can be 0%, and the second preset value B n % can be 3%; or, the first preset value B0% can be 0.3%, and the second preset value B n % can be 5%; or, the first preset value B0% can be 0.3%, and the second preset value B n % can be 3%.

[0055] The difference in the amount of conductive agent used between single-layer thin-coated electrodes and single-layer thick-coated electrodes is significant. Therefore, in some other embodiments, the first preset value B0% and the second preset value B...n The percentage can be adjusted accordingly; for example, for areal densities ≤ 5 mg / cm³. 2 For a single-layer thin-coated electrode, the first preset value B0% can be 0%, and the second preset value B n % can be 1%; for areal density ≥ 8 mg / cm³ 2 For a single-layer thick-coated electrode, the first preset value B0% can be 3%, and the second preset value B n The percentage can be 5%. This reduces the number of monolayer coated electrodes n that need to be prepared, not only ensuring accurate and optimal dosage of conductive agent, but also simplifying the preparation process and improving efficiency.

[0056] After preparing n single-layer coated electrodes with equal areal density but different amounts of conductive agent, each electrode is used to fabricate a battery, and the internal resistance of the battery is tested. It should be noted that if the n electrodes are positive, the same negative electrode is used to prepare the corresponding n batteries, meaning the amount of conductive agent in all negative electrodes remains the same. Conversely, if the n electrodes are negative, the same positive electrode is used to prepare the corresponding n batteries, meaning the amount of conductive agent in all positive electrodes remains the same. Furthermore, the main material, conductive agent, and other additives in the n electrodes can all be of the same type; this avoids the potential impact on the battery internal resistance test results due to differences in at least one of the main material, conductive agent, or other additives among the different electrodes, thus facilitating the accurate determination of the optimal amount of conductive agent in the single-layer coated electrode.

[0057] It should be noted that the specific preparation methods of the positive electrode, negative electrode and battery in the embodiments of this application are not limited, and any method well known to those skilled in the art can be used for preparation.

[0058] Specifically, a method for testing battery internal resistance could be, for example, discharging the battery at a rate of 2C for 30 seconds at 25°C and 50% SOC (State of Charge). The internal resistance DCR is calculated as: (Voltage before discharge V1 - Voltage after discharge V2) / Discharge current I. Of course, this application does not exclude the possibility of using other testing methods to measure battery internal resistance.

[0059] After measuring the internal resistance of batteries made from n single-layer coated electrodes, the amount of conductive agent in each single-layer coated electrode is used as the independent variable x, and the internal resistance of the corresponding battery is used as the dependent variable y. A fitting curve is obtained, and the minimum x value corresponding to the absolute value of the slope of the fitting curve reaching the preset slope value is determined as the optimal amount of conductive agent in the single-layer coated electrode.

[0060] It is understandable that as the amount of conductive agent in the single-layer coated electrode increases, the internal resistance of the corresponding battery will show a trend of first rapidly decreasing and then stabilizing. That is, after the amount of conductive agent increases to a certain value, the internal resistance of the battery basically no longer decreases with the increase of the amount of conductive agent. Therefore, in the above fitting curve, there will be a turning point (also called an inflection point), and the x value corresponding to the inflection point can be considered as the optimal amount of conductive agent. In the embodiments of this application, the inflection point of the fitting curve can be located relatively accurately by the change in the absolute value of the slope of the fitting curve. Specifically, the minimum x value corresponding to the absolute value of the slope of the fitting curve reaching the preset slope value can be determined as the optimal amount of conductive agent in the single-layer coated electrode. The smaller the preset slope value, the more accurate the determined optimal amount of conductive agent. In some specific embodiments, the preset slope value can be less than or equal to 5% of the maximum value of the absolute value of the slope of the fitting curve, preferably less than or equal to 3% of the maximum value of the absolute value of the slope of the fitting curve, and more preferably 0.

[0061] In some embodiments, in step S1, m ≥ 3. That is, the optimal amount of conductive agent in the monolayer coated electrode under at least 3 different areal densities is determined. In this way, the accuracy of the functional relationship obtained in step S2 based on the optimal amount of conductive agent in the monolayer coated electrode under different areal densities, with areal density as the independent variable G and conductive agent amount as the dependent variable B, will be higher.

[0062] The following example, using m=3, illustrates the specific steps for performing steps S1 and S2 above.

[0063] First, perform step S1 to determine the optimal amount of conductive agent in the single-layer coated electrode at the three areal densities. Specifically:

[0064] 1) Under an areal density of G1, prepare n1 single-layer coated electrodes with equal areal densities but different amounts of conductive agent. From the first to the n1th single-layer coated electrode, the mass percentage of conductive agent B% increases from 0% to 3%, with a gradient set for every 0.3% (i.e., n1 = 11). The mass percentage of other additives C% remains constant, and the mass percentage of the main material A% is adjusted accordingly to maintain A + B + C = 100. Prepare batteries from the n1 single-layer coated electrodes and measure the internal resistance DCR of each battery. Using the amount of conductive agent in each single-layer coated electrode as the independent variable x and the internal resistance of the corresponding battery as the dependent variable y, fit the curve to obtain a fitting curve. The minimum x value corresponding to the absolute value of the slope of the fitting curve reaching the preset slope value (e.g., close to 0) is determined as the optimal amount B1 of conductive agent in the single-layer coated electrode with an areal density of G1.

[0065] 2) Under an areal density of G2, prepare n2 single-layer coated electrodes with equal areal densities but different amounts of conductive agent. From the first to the n2nd single-layer coated electrode, the mass percentage of conductive agent B% increases from 0% to 3%, with a gradient set for every 0.3% (i.e., n2 = 11). The mass percentage of other additives C% remains constant, and the mass percentage of the main material A% is adjusted accordingly to maintain A + B + C = 100. Prepare batteries from the n2 single-layer coated electrodes and measure the internal resistance DCR of each battery. Using the amount of conductive agent in each single-layer coated electrode as the independent variable x and the internal resistance of the corresponding battery as the dependent variable y, fit the curve to obtain a fitting curve. The minimum x value corresponding to the absolute value of the slope of the fitting curve reaching the preset slope value (e.g., close to 0) is determined as the optimal amount of conductive agent B2 in the single-layer coated electrode with an areal density of G2.

[0066] 3) Under an areal density of G3, prepare n3 single-layer coated electrodes with equal areal densities but different amounts of conductive agent. From the first to the n3rd single-layer coated electrode, the mass percentage of conductive agent B% increases from 0% to 3%, with a gradient set for every 0.3% (i.e., n3 = 11). The mass percentage of other additives C% remains constant, and the mass percentage of the main material A% is adjusted accordingly to maintain A + B + C = 100. Prepare batteries from the n3 single-layer coated electrodes and measure the internal resistance DCR of each battery. Using the amount of conductive agent in each single-layer coated electrode as the independent variable x and the internal resistance of the corresponding battery as the dependent variable y, fit the curve to obtain a fitting curve. The minimum x value corresponding to the absolute value of the slope of the fitting curve reaching the preset slope value (e.g., close to 0) is determined as the optimal amount of conductive agent B3 in the single-layer coated electrode with an areal density of G3.

[0067] Next, step S2 is executed. Based on the optimal amount of conductive agent in the single-layer coated electrode under different areal densities, a fitting curve between the optimal amount of conductive agent in the single-layer coated electrode and the areal density of the single-layer coated electrode is constructed, and a functional relationship is obtained with areal density as the independent variable G and conductive agent amount as the dependent variable B.

[0068] Specifically, based on the data sets (G1, B1), (G2, B2), and (G3, B3) of the optimal amount of conductive agent in the single-layer coated electrode under different areal densities obtained in step S1, a functional relationship B = F(G) with G as the independent variable and B as the dependent variable is fitted using these data.

[0069] The above example uses m=3. It can be understood that the larger the value of m, that is, the more surface density gradients are set, the more data sets are obtained in step S1, and the higher the accuracy of the function relationship obtained in step S2.

[0070] In some embodiments, please refer to Figure 2After step S2, the method for determining the amount of conductive agent in each layer of the multilayer coated electrode may also include a step of detecting the accuracy of the functional relationship:

[0071] S21. Based on the functional relationship, obtain the amount of the first conductive agent at a certain areal density, and fabricate the first test single-layer coated electrode sheet; keeping the areal density constant, reduce the amount of conductive agent based on the first amount of conductive agent to fabricate the second test single-layer coated electrode sheet; keeping the areal density constant, increase the amount of conductive agent based on the first amount of conductive agent to fabricate the third test single-layer coated electrode sheet; the absolute value of the difference between the amount of conductive agent and the first amount of conductive agent in the second and third test single-layer coated electrode sheets is less than the minimum difference of the amount of conductive agent in the different test single-layer coated electrode sheets in step S1;

[0072] Specifically, any areal density g1 can be substituted into the functional relationship B = F(G) obtained in step S2 to obtain the amount of the first conductive agent b1. Then, a first inspection single-layer coated electrode sheet is made with the main material mass percentage A%, the first conductive agent mass percentage b1, and the other additive mass percentage C%. A second inspection single-layer coated electrode sheet is made with the main material mass percentage (A% - 0.2%), the conductive agent mass percentage (b1 + 0.2%), and the other additive mass percentage C. A third inspection single-layer coated electrode sheet is made with the main material mass percentage (A% + 0.2%), the conductive agent mass percentage (b1 - 0.2%), and the other additive mass percentage C.

[0073] It should be noted that the reduction and increase of the conductive agent content in the second and third test monolayer coated electrodes by 0.2% relative to the first conductive agent content is merely an example. Referring to the above embodiment, in step S1, when the areal densities are G1, G2, and G3, the minimum increase gradient of the conductive agent content in the multiple test monolayer coated electrodes at each areal density is 0.3%. In practical applications, the absolute value of the difference between the conductive agent content in the second and third test monolayer coated electrodes and the first conductive agent content should be less than the minimum difference in the conductive agent content in the different test monolayer coated electrodes in step S1. This can better ensure the reliability of the accuracy detection of the functional relationship.

[0074] S22. The first inspection single-layer coated electrode, the second inspection single-layer coated electrode, and the third inspection single-layer coated electrode are respectively made into a first battery, a second battery, and a third battery, and the internal resistance of each battery is tested.

[0075] The method for testing the battery internal resistance can be understood by referring to the method described in the above embodiments, and will not be repeated here. The internal resistances of the first, second, and third batteries can be denoted as DCR1, DCR2, and DCR3, respectively.

[0076] S23. Determine whether the first internal resistance of the first battery, the second internal resistance of the second battery, and the third internal resistance of the third battery meet the following conditions: the second internal resistance is greater than the first internal resistance and the relative difference between the second internal resistance and the first internal resistance is greater than or equal to the first preset difference, and the relative difference between the third internal resistance and the first internal resistance is less than or equal to the second preset difference, and the first preset difference is greater than the second preset difference.

[0077] If the above conditions are met, continue to step S3; if the above conditions are not met, increase the value of m in step S1, and obtain the functional relationship again according to steps S1 and S2.

[0078] In step S23, DCR2 > DCR1, and the relative difference between them is greater than or equal to the first preset value, while the relative difference between DCR1 and DCR3 is less than or equal to the second preset difference. The first preset difference is greater than the second preset difference, thus determining that DCR2 is greater than DCR1. Since DCR1 and DCR3 are essentially equal, it can be considered that DCR2 > DCR1 ≈ DCR3. In this case, it indicates that reducing the amount of conductive agent based on the first conductive agent dosage will lead to an increase in the internal resistance of the corresponding battery, while increasing the amount of conductive agent based on the first conductive agent dosage will keep the internal resistance of the battery essentially unchanged. That is, under the condition of the first conductive agent dosage, the internal resistance of the battery has reached the lowest stable level. Therefore, it can be considered that using the first conductive agent dosage as the optimal dosage of conductive agent in a single-layer coated electrode at g1 areal density is relatively accurate. In other words, the accuracy of the functional relationship B = F(G) obtained in step S2 meets the requirements.

[0079] The relative differences between DCR2 and DCR1, and between DCR3 and DCR1, represent the percentage decrease of the smaller resistance relative to the larger resistance. For example, when DCR2 ≥ DCR1, the relative difference between the second internal resistance and the first internal resistance = ((DCR2 - DCR1) / DCR2) * 100%. When DCR1 ≥ DCR3, the relative difference between the third internal resistance and the first internal resistance = ((DCR1 - DCR3) / DCR1) * 100%.

[0080] In some specific embodiments, the second preset difference can be less than or equal to 5%. That is, when the relative difference between DCR1 and DCR3 is within 5%, DCR1 and DCR3 can be considered to be essentially equal. The first preset difference is greater than the second preset difference, and the first preset difference is greater than 5%. Specifically, the first preset difference can be, for example, 10%, 20%, 30%, 40%, 50%, or a larger value, which can be determined based on the difference in the amount of conductive agent used in the first and second test single-layer coated electrodes.

[0081] In this embodiment, an additional step is added to check the accuracy of the functional relationship B = F(G) obtained in step S2. If the accuracy requirement is not met, the value of m in step S1 can be increased, i.e., more surface density gradient can be added in step S1, to obtain a more accurate functional relationship B = F(G) in step S2. If the accuracy of the functional relationship obtained after the first increase in the value of m still does not meet the requirement after testing, the value of m can be increased again, and the functional relationship can be obtained again until the accuracy of the functional relationship meets the requirement.

[0082] Finally, step S3 is executed. For each active material layer in the multilayer coated electrode, the sum of the surface density of the active material layer and all active material layers on the surface of the active material layer away from the current collector is used as the independent variable G in the functional relationship, and the resulting dependent variable B is used as the amount of conductive agent in the active material layer.

[0083] Please refer to Figure 3 The multilayer coated electrode may include a current collector 100 and multiple active material layers 200 sequentially stacked on at least one surface of the current collector 100 along its thickness direction. From the direction closest to the current collector to the direction furthest away from it, the multiple active material layers 200 sequentially include a first active material layer 201, ..., an Nth active material layer 204 (N is greater than or equal to 2). Each active material layer contains active materials. The current generated by the active materials during charging and discharging is collected by the current collector and then output to an external circuit. That is, the current generated by the active materials in the upper active material layer furthest from the current collector during charging and discharging needs to pass through the lower active material layer closest to the current collector to reach the current collector for collection. For example, if the capacity of each active material layer in the multiple active material layers 200 is C, then the theoretical maximum charge passing through the Nth active material layer 204 is C, the theoretical maximum charge passing through the (N-1)th active material layer is 2C, and so on, the theoretical maximum charge passing through the second active material layer is (N-1)C, and the theoretical maximum charge passing through the first active material layer 201 is nC. Theoretically, the maximum charge that can pass through an active material layer closer to the current collector is greater. Therefore, the amount of conductive agent required for an active material layer closer to the current collector is higher. That is, the actual amount of conductive agent required gradually decreases from the first active material layer 201 to the Nth active material layer 204. Therefore, in this embodiment, for each active material layer in the multilayer coated electrode, the sum of the areal densities of the active material layer and all active material layers located on the surface of the active material layer away from the current collector is used as the independent variable G in the functional relationship, and the resulting dependent variable B is used as the amount of conductive agent in that active material layer. This allows the determined amount of conductive agent in each active material layer of the multilayer coated electrode to gradually decrease, which not only better ensures the conductivity of the multilayer coated electrode and reduces the internal resistance of the battery, but also helps to improve the energy density and dynamic performance of the battery.

[0084] For details, please continue to refer to Figure 3 Taking N greater than or equal to 4 as an example, the areal densities of the first active material layer 201 to the Nth active material layer 204 are denoted as G1', G2', G3', ..., G... N According to the functional relationship B = F(G) obtained in step S2, the amount of conductive agent in the first active material layer 201 is B1' = F(G1' + G2' + G3' + ... + G...). N The amount of conductive agent in the second active material layer 202 is B2' = F(G2' + G3' + ... + G). N The amount of conductive agent in the third active material layer 203 is B3' = F(G3' + ... + G). N '), and so on, the amount of conductive agent B in the Nth active material layer 204 N '=F(G N ').

[0085] This application also provides an application of the method for determining the amount of conductive agent in each layer of the multilayer coated electrode as described in any of the above embodiments in the preparation of the electrode. The electrode here may include a positive electrode and / or a negative electrode. That is, the method for determining the amount of conductive agent in each layer of the multilayer coated electrode in this application is applicable to both multilayer coated positive electrodes and multilayer coated negative electrodes, and has high practical application value.

[0086] The following example illustrates the application of the method for determining the amount of conductive agent in each layer of a multilayer coated electrode in the preparation of a negative electrode, further demonstrating the technical solution of this application.

[0087] In this embodiment, the negative electrode active material layer in the negative electrode sheet includes graphite (the main negative electrode material), conductive carbon black SP (conductive agent), sodium carboxymethyl cellulose CMC (binder), and styrene-butadiene rubber SBR (binder). The mass percentages of graphite, conductive carbon black, CMC, and SBR in the negative electrode active material layer are A%, B%, 1.5%, and 2%, respectively, where A+B = 96.5. The compaction density of the negative electrode sheet is 1.6 g / cc. The N / P ratio (the ratio of negative electrode capacity to positive electrode capacity) is 1.12.

[0088] The same positive electrode sheet is used in the battery fabrication. The positive electrode active material layer in the positive electrode sheet includes a hexagonal ternary positive electrode material (the main positive electrode material), a binder PVDF, conductive carbon black SP (conductive agent), and carbon nanotubes CNT (conductive agent). The mass percentages of the hexagonal ternary positive electrode material, PVDF, conductive carbon black, and CNT in the positive electrode active material layer are 90%, 2%, 4%, and 4%, respectively. The compaction density of the positive electrode sheet is 3.45 g / cc.

[0089] First, with a surface density of 8 mg / cm³2 10mg / cm 2 12mg / cm 2 For each areal density, 11 single-layer coated negative electrode sheets with equal areal densities but different amounts of conductive agent were fabricated for testing. The formulations of the negative electrode main material (graphite), conductive agent (SP), and binder (CMC+SBR) in each single-layer coated negative electrode sheet are shown in Tables 1 to 3 below. The areal density of each single-layer coated negative electrode sheet in Table 1 is 8 mg / cm³. 2 The areal density of each monolayer coated negative electrode sheet to be tested in Table 2 is 10 mg / cm³. 2 The areal density of each monolayer coated negative electrode sheet in Table 3 is 12 mg / cm³. 2 .

[0090] Next, the various single-layer coated negative electrode sheets prepared under different areal densities were combined with the aforementioned positive electrode sheets to form batteries. These batteries were then discharged at 2C for 30 seconds at 25°C and 50% SOC. The internal resistance (DCR) of the batteries was measured, where DCR = (voltage before discharge V1 - voltage after discharge V2) / discharge current I. The internal resistance test results for each single-layer coated negative electrode sheet are shown in Tables 1 to 3.

[0091] Table 1 shows that the surface density is 8 mg / cm³. 2 At that time, the formulation of each single-layer coated negative electrode and the internal resistance of the corresponding battery were determined.

[0092]

[0093]

[0094] Table 2 shows the surface density as 10 mg / cm³. 2 At that time, the formulation of each single-layer coated negative electrode and the internal resistance of the corresponding battery were determined.

[0095] 1 96.50％ 0.00％ 1.50％ 2.00％ 163.9 2 96.20％ 0.30％ 1.50％ 2.00％ 134.6 3 95.90％ 0.60％ 1.50％ 2.00％ 111.8 4 95.60％ 0.90％ 1.50％ 2.00％ 89.7 5 95.30％ 1.20％ 1.50％ 2.00％ 65.8 6 95.00％ 1.50％ 1.50％ 2.00％ 41.2 7 94.70％ 1.80％ 1.50％ 2.00％ 41.0 8 94.40％ 2.10％ 1.50％ 2.00％ 41.1 9 94.10％ 2.40％ 1.50％ 2.00％ 40.9 10 93.80％ 2.70％ 1.50％ 2.00％ 40.7 11 93.50％ 3.00％ 1.50％ 2.00％ 41.0

[0096] Table 3 shows that the surface density is 12 mg / cm³. 2 At that time, the formulation of each single-layer coated negative electrode and the internal resistance of the corresponding battery were determined.

[0097] 1 96.50％ 0.00％ 1.50％ 2.00％ 261.3 2 96.20％ 0.30％ 1.50％ 2.00％ 223.6 3 95.90％ 0.60％ 1.50％ 2.00％ 192.8 4 95.60％ 0.90％ 1.50％ 2.00％ 154.3 5 95.30％ 1.20％ 1.50％ 2.00％ 121.8 6 95.00％ 1.50％ 1.50％ 2.00％ 98.9 7 94.70％ 1.80％ 1.50％ 2.00％ 76.8 8 94.40％ 2.10％ 1.50％ 2.00％ 59.7 9 94.10％ 2.40％ 1.50％ 2.00％ 59.6 10 93.80％ 2.70％ 1.50％ 2.00％ 59.5 11 93.50％ 3.00％ 1.50％ 2.00％ 59.6

[0098] Next, based on the test data in Tables 1 to 3, for the 11 tested single-layer coated negative electrode sheets at various areal densities, the SP content (conductive agent dosage) of each tested single-layer coated electrode sheet was used as the independent variable x, and the corresponding internal resistance of the battery was used as the dependent variable y. A fitting curve was obtained, and the minimum x value corresponding to the absolute value of the slope of the fitting curve reaching a preset slope value (close to 0) was determined as the optimal dosage of conductive agent in the single-layer coated electrode sheet at that areal density. For an areal density of 8 mg / cm³... 2For single-layer coated electrodes, the optimal amount of conductive agent can be determined from the values ​​in Table 1 to be 0.9%. For single-layer coated electrodes with an areal density of 10 mg / cm², the optimal amount of conductive agent can be determined from the values ​​in Table 2 to be 1.5%. For single-layer coated electrodes with an areal density of 12 mg / cm², the optimal amount of conductive agent can be determined from the values ​​in Table 3 to be 2.1%.

[0099] Next, the function B = F(G) with surface density G as the independent variable and conductive agent dosage B as the dependent variable was fitted using (8, 0.9), (10, 1.5), and (12, 2.1). The fitting results are as follows: Figure 4 As shown, the fitted function is B = 0.3G - 1.5, where G is in mg / cm² and B is in %. Substituting the areal density (mg / cm²) into the formula, we get B in %, meaning the amount of conductive agent used is expressed as the mass percentage of the conductive agent in the active material layer.

[0100] Next, the accuracy of the obtained functional relationship B = 0.3G - 1.5 will be tested.

[0101] Specifically, firstly, the surface density is 9 mg / cm³. 2 Substituting into the functional relationship B = 0.3G - 1.5, the amount of conductive agent is found to be 1.2%. This 1.2% conductive agent amount is used as the amount of conductive agent in the first test single-layer coated electrode. Next, the first test single-layer coated electrode, the second test single-layer coated electrode, and the third test single-layer coated electrode are prepared according to the following formula. The prepared first test single-layer coated electrode, the second test single-layer coated electrode, and the third test single-layer coated electrode are combined with the positive electrode sheet described in the above steps to form a battery. The internal resistance of each battery is tested using the same method as in the above steps.

[0102] ① In the first test single-layer coated electrode sheet, the graphite main material content is 96.3%, the conductive agent SP content is 1.2%, and the total content of other additives CMC and SBR is 3.5%; the DCR1 of the battery made using the first test single-layer coated electrode sheet is 33.5mΩ;

[0103] ② In the second test single-layer coated electrode, the graphite main material content is 96.5%, the conductive agent SP content is 1.0%, and the total content of other additives CMC and SBR is 3.5%; the DCR2 of the battery made using the second test single-layer coated electrode is 59.4mΩ;

[0104] ③ In the third test single-layer coated electrode, the graphite content is 96.1%, the conductive agent SP content is 1.4%, and the total content of other additives CMC and SBR is 3.5%; the DCR3 of the battery made using the third test single-layer coated electrode is 32.6mΩ.

[0105] Based on the above test results, the relative difference between DCR3 and DCR1 is ((DCR1-DCR3) / DCR1)*100% = 2.7%, which means the second preset difference is less than or equal to 5%. The relative difference between DCR2 and DCR1 is ((DCR2-DCR1) / DCR2)*100% = 43.6%, which means the first preset difference is greater than the second preset difference. Therefore, the test results of the three battery internal resistances satisfy DCR2>DCR1≈DCR3, which indicates that the accuracy of the fitted function B=0.3G-1.5 obtained in the above steps meets the requirements.

[0106] Finally, the amount of conductive agent in each layer of the multilayer coated electrode was determined. Taking a three-layer coated negative electrode as an example, in the three-layer coated negative electrode, from the surface of the current collector to the direction away from the current collector, the first active material layer to the third active material layer are stacked sequentially on the surface of the current collector, and the areal densities of the first active material layer to the third active material layer are 2 mg / cm³, respectively. 2 4mg / cm 2 and 8mg / cm 2 Based on the functional relationship B = 0.3G - 1.5, the amount of conductive agent in the first active material layer can be determined as 0.3*(2+4+8) - 1.5 = 2.7%; the amount of conductive agent in the second active material layer is 0.3*(4+8) - 1.5 = 2.1%; and the amount of conductive agent in the third active material layer is 0.3*8 - 1.5 = 0.9%.

[0107] After determining the amount of conductive agent (SP) in each active material layer of the three-layer coated negative electrode, battery examples and comparative examples were prepared. The coating type, areal density, and active material layer formulations of the negative electrodes in the battery examples and comparative examples are shown in Table 4 below. In both the battery examples and comparative examples, the negative electrode active material used was graphite, the conductive agent was SP, and the binder was a combination of CMC and SBR. The positive electrode in both the battery examples and comparative examples used the positive electrode described in the above steps. The battery was obtained after assembling the positive and negative electrodes.

[0108] Table 4

[0109]

[0110]

[0111] The internal resistance and energy density of the batteries in the battery examples and comparative examples were tested. The method for testing the internal resistance of the batteries was the same as that in the previous steps. The method for testing the energy density of the batteries was as follows: First, the batteries were left to stand at 25°C for 30 minutes; then, they were charged at a constant current rate of 1C to 4.2V, and then charged at a constant voltage rate to the cutoff current of 0.05C; next, they were left to stand for 30 minutes, and then discharged at a rate of 1C to 2.8V. The total discharge energy during the discharge process was recorded as W. The cell was weighed and the weight of the cell was recorded as G; the energy density of the battery = W / G. The test results are shown in Table 5.

[0112] Table 5

[0113]

[0114] As shown in Table 5, when the sum of the areal densities of the three active material layers in a three-layer coated negative electrode is the same as that of a single active material layer in a single-layer coated negative electrode, the difference in internal resistance (DCR) between the three-layer coated negative electrode and the single-layer coated negative electrode is approximately 0.27%, which can be considered essentially the same. However, the energy density of the battery corresponding to the three-layer coated negative electrode is 1.28% higher than that of the battery corresponding to the single-layer coated negative electrode. Therefore, the method for determining the amount of conductive agent in each layer of the multi-layer coated electrode provided in this application, by gradually reducing the amount of conductive agent in each active material layer from the layer closest to the current collector to the layer furthest from the current collector, not only maintains a battery internal resistance similar to that of a single-layer coated electrode at the same areal density, but also improves the battery energy density. Although the increase in battery energy density is relatively small, the relative benefit is very high because the amount of conductive agent in the active material layer is inherently small, and it can be considered to have a significant effect on improving battery energy density. Moreover, the method for determining the amount of conductive agent in each layer of the multilayer coated electrode provided in this application has a more obvious advantage in multilayer thick coated electrodes.

[0115] This invention provides a method for quantitatively determining the amount of conductive agent in each layer of a multilayer coated electrode. It provides a clear and quantitative definition of the amount of conductive agent in each layer of a multilayer coated electrode, filling the gap in the definition of the amount of conductive agent in each layer of a multilayer coated electrode. While ensuring the conductivity of the multilayer coated electrode, it can also improve the energy density and dynamic performance of the battery.

[0116] It should be noted that the method for determining the amount of conductive agent in each layer of the multilayer coated electrode provided in this application belongs to the same concept as the application embodiment; the technical features in the technical solutions described in each embodiment can be arbitrarily combined without conflict.

[0117] It should be understood that the above embodiments are exemplary and not intended to encompass all possible implementations of this application. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of the present invention and do not limit the scope of protection of this patent.

Claims

1. A method for determining the amount of conductive agent in each layer of a multilayer coated electrode, characterized in that, The multilayer coated electrode includes a current collector and multiple layers of active material sequentially stacked on at least one surface of the current collector; the method includes the following steps: S1: Determine the optimal amount of conductive agent in single-layer coated electrodes with m different areal densities, wherein the single-layer coated electrode comprises a single-layer active material layer, and m ≥ 3; the method for determining the optimal amount for each single-layer coated electrode includes: Prepare n single-layer coated electrodes with equal areal density and different amounts of conductive agent, n≥5. Fabricate each of the single-layer coated electrodes into a battery and test the internal resistance of the battery. Using the amount of conductive agent of the single-layer coated electrode as the independent variable x and the internal resistance of the corresponding battery as the dependent variable y, fit the curve to obtain a fitting curve. The minimum x value corresponding to the absolute value of the slope of the fitting curve reaching the preset slope value is determined as the optimal amount of conductive agent in the single-layer coated electrode. S2: Based on the optimal amount of conductive agent in monolayer coated electrodes under different areal densities, a fitting curve between the optimal amount of conductive agent in monolayer coated electrodes and the areal density of monolayer coated electrodes is constructed, and a functional relationship is obtained with areal density as independent variable G and conductive agent amount as dependent variable B. S3: For each active material layer in the multilayer coated electrode, the sum of the surface density of the active material layer and all active material layers on the surface of the active material layer away from the current collector is taken as the independent variable G in the functional relationship, and the resulting dependent variable B is taken as the amount of conductive agent in the active material layer.

2. The method for determining the amount of conductive agent in each layer of the multilayer coated electrode according to claim 1, characterized in that, In step S1, the preset slope value is less than or equal to 5% of the maximum absolute value of the slope of the fitted curve.

3. The method for determining the amount of conductive agent in each layer of the multilayer coated electrode according to claim 1, characterized in that, The preset slope value is 0.

4. The method for determining the amount of conductive agent in each layer of the multilayer coated electrode according to claim 1, characterized in that, In step S1, n single-layer coated electrodes with equal areal density but different amounts of conductive agent are fabricated, including: The amount of conductive agent in the n single-layer coated electrodes to be tested is increased sequentially from a first preset value to a second preset value; wherein, the single increase in the amount of conductive agent is less than or equal to 33% of the difference between the second preset value and the first preset value.

5. The method for determining the amount of conductive agent in each layer of the multilayer coated electrode according to claim 4, characterized in that, The single increase value is less than or equal to 20% of the difference between the second preset value and the first preset value.

6. The method for determining the amount of conductive agent in each layer of the multilayer coated electrode according to claim 5, characterized in that, The single increase value is less than or equal to 10% of the difference between the second preset value and the first preset value.

7. The method for determining the amount of conductive agent in each layer of the multilayer coated electrode according to claim 4, characterized in that, The single increment value is a fixed value.

8. The method for determining the amount of conductive agent in each layer of the multilayer coated electrode according to claim 4, characterized in that, The amount of conductive agent in the single-layer coated electrode is the mass percentage of the conductive agent in the single-layer active material layer; the first preset value is less than or equal to 0.3%; the second preset value is greater than or equal to 3%.

9. The method for determining the amount of conductive agent in each layer of the multilayer coated electrode according to claim 8, characterized in that, The first preset value is 0%, and the second preset value is greater than or equal to 5%.

10. The method for determining the amount of conductive agent in each layer of the multilayer coated electrode according to any one of claims 4 to 9, characterized in that, Following step S2, the method further includes a step of checking the accuracy of the functional relationship: S21. Based on the functional relationship, the amount of the first conductive agent at a certain surface density is obtained, and the first test single-layer coated electrode is prepared. Keeping the areal density constant, reduce the amount of conductive agent based on the amount of the first conductive agent to produce a second test single-layer coated electrode sheet; keep the areal density constant, increase the amount of conductive agent based on the amount of the first conductive agent to produce a third test single-layer coated electrode sheet. The absolute values ​​of the differences between the amount of conductive agent in the second and third test single-layer coated electrode sheets and the amount of the first conductive agent are both less than the minimum difference in the amount of conductive agent in different test single-layer coated electrode sheets in step S1. S22. The first test single-layer coated electrode, the second test single-layer coated electrode, and the third test single-layer coated electrode are respectively made into a first battery, a second battery, and a third battery, and the internal resistance of each battery is tested. S23. Determine whether the first internal resistance of the first battery, the second internal resistance of the second battery, and the third internal resistance of the third battery satisfy the following conditions: the second internal resistance is greater than the first internal resistance and the relative difference between the second internal resistance and the first internal resistance is greater than or equal to a first preset difference, and the relative difference between the third internal resistance and the first internal resistance is less than or equal to a second preset difference, and the first preset difference is greater than the second preset difference. If the above conditions are met, proceed to step S3; If the above conditions are not met, increase the value of m in step S1, and re-obtain the functional relationship according to steps S1 and S2.

11. The method for determining the amount of conductive agent in each layer of the multilayer coated electrode according to claim 10, characterized in that, The second preset difference is less than or equal to 5%.

12. The method for determining the amount of conductive agent in each layer of the multilayer coated electrode according to any one of claims 1 to 11 is applied in the preparation of the electrode; the electrode includes a positive electrode and / or a negative electrode.

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