Method for determining dosage of conductive agent in each layer of multi-layer coated pole piece and application

Abstract

The invention relates to a method for determining the dosage of a conductive agent in each layer of a multi-layer coated pole piece and application, and the method comprises the following steps: determining the optimal dosage of the conductive agent in m single-layer coated pole pieces under different surface densities, the single-layer coated pole pieces comprising single-layer active material layers; based on the optimal use amount of the conductive agent in the single-layer coated pole piece under different surface densities, constructing a fitting curve between the optimal use amount of the conductive agent in the single-layer coated pole piece and the surface density of the single-layer coated pole piece, and obtaining a function relation taking the surface density as an independent variable G and the use amount of the conductive agent as a dependent variable B; and for each active substance layer in the multi-layer coated pole piece, taking the sum of the surface densities of the active substance layer and all active substance layers on the surface, far away from the current collector, of the active substance layer as an independent variable G in the functional relation, and taking an obtained dependent variable B as the dosage of the conductive agent in the active substance layer. Therefore, accurate quantification of the use amount of the conductive agent in each layer of the multi-layer coated pole piece is realized.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a method for determining the amount of conductive agent used in each layer of a multi-layer coated pole piece and its application. Background Art

[0002] With the large-scale application of secondary batteries in electric vehicles, energy storage systems, consumer electronics and other fields, improving the energy density and power density of secondary batteries has become one of the hot research directions. When using the same type of active material, the existing technology usually adopts the method of increasing the coating weight (surface density) of the active material layer to improve the energy density of the battery. However, with the increase in coating weight, it is inevitable that the internal resistance of the battery will increase, which may lead to a series of problems such as battery capacity attenuation, increased heat generation, decreased output voltage, decreased power output, reduced charging efficiency and thermal runaway of the battery.

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

[0004] However, the industry currently lacks a clear solution for determining the amount of conductive agent used in each active material layer of a multi-layer coated electrode during production. Currently, this determination is largely empirical, resulting in significant trial-and-error costs. Summary of the Invention

[0005] In view of this, embodiments of the present application provide a method and application for determining the amount of conductive agent used in each layer of a multi-layer coated electrode to solve at least one problem existing in the background technology.

[0006] In a first aspect, an embodiment of the present application provides a method for determining the amount of conductive agent used in each layer of a multi-layer coated electrode, characterized in that the multi-layer coated electrode includes a current collector and multiple active material layers sequentially stacked on at least one side surface of the current collector; the method comprises the following steps:

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

[0008] Prepare n single-layer coated electrode sheets to be tested with equal surface density and different amounts of conductive agent, make batteries with each of the single-layer coated electrode sheets to be tested, and measure the internal resistance of the batteries. Use the conductive agent amount of the single-layer coated electrode sheet to be tested as the independent variable x and the internal resistance of the corresponding battery as the dependent variable y to obtain a fitting curve. The minimum x value corresponding to the absolute value of the slope of the fitting curve reaching a preset slope value is determined as the optimal amount of conductive agent in the single-layer coated electrode sheet;

[0009] S2: Based on the optimal amount of conductive agent in the single-layer coated electrode at different surface densities, a fitting curve is constructed between the optimal amount of conductive agent in the single-layer coated electrode and the surface density of the single-layer coated electrode, and a functional relationship is obtained with the surface density as the independent variable G and the amount of conductive agent as the dependent variable B;

[0010] S3: For each active material layer in the multi-layer coated electrode, the sum of the surface density 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.

[0011] In combination with the first aspect of the present application, in an optional implementation manner, in step S1, m≥3.

[0012] In combination with the first aspect of the present application, in an optional implementation manner, in step S1, the preset slope value is less than or equal to 5% of the maximum absolute value of the slope of the fitting curve, and is preferably 0.

[0013] In conjunction with the first aspect of the present application, in an optional embodiment, in step S1, n single-layer coated electrodes to be tested with equal surface density and different amounts of conductive agent are prepared, 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 combination with the first aspect of the present application, in an optional implementation manner, the single increase 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 combination with the first aspect of the present application, in an optional implementation manner, the single increase value is a fixed value.

[0017] In combination with the first aspect of the present application, in an optional embodiment, the amount of conductive agent in the single-layer coated electrode is the mass proportion of the conductive agent in the single-layer 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 the present application, in an optional implementation manner, after step S2, a step of detecting the accuracy of the functional relationship is further included:

[0019] S21, obtaining the amount of the first conductive agent at a certain surface density according to the functional relationship, and producing a first test single-layer coated electrode;

[0020] Keeping the surface density unchanged, the amount of conductive agent is reduced on the basis of the first amount of conductive agent, and a second test single-layer coated electrode piece is produced; keeping the surface density unchanged, the amount of conductive agent is increased on the basis of the first amount of conductive agent, and a third test single-layer coated electrode piece is produced;

[0021] The absolute values ​​of the differences between the amounts of the conductive agent in the second test single-layer coated electrode piece and the third test single-layer coated electrode piece and the amount of the first conductive agent are both smaller than the minimum difference in the amounts of the conductive agent in different single-layer coated electrode pieces to be tested in step S1;

[0022] S22, respectively fabricating the first test single-layer coated electrode piece, the second test single-layer coated electrode piece, and the third test single-layer coated electrode piece into a first battery, a second battery, and a third battery, and testing the internal resistance of each battery;

[0023] S23. Determine whether a first internal resistance of the first battery, a second internal resistance of the second battery, and a third internal resistance of the third battery meet the following conditions: the second internal resistance is greater than the first internal resistance, and a relative difference between the second internal resistance and the first internal resistance is greater than or equal to a first preset difference, and a 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, the value of m in step S1 is increased, and the functional relationship is obtained again according to steps S1 and S2.

[0026] In combination with the first aspect of the present application, in an optional implementation manner, the second preset difference is less than or equal to 5%.

[0027] In a second aspect, an embodiment of the present application provides the application of a method for determining the amount of conductive agent used in each layer of a multi-layer coated electrode as described in any one of the first aspects in preparing an electrode; optionally, the electrode includes a positive electrode and / or a negative electrode.

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

[0029] The embodiments of the present application provide a method for determining the amount of conductive agent in each layer of a multi-layer coated electrode and its application. The multi-layer coated electrode includes a current collector and a multi-layer active material layer stacked in sequence on at least one side surface of the current collector. In the method for determining the amount of conductive agent in each layer of a multi-layer coated electrode, the optimal amount of conductive agent in a single-layer coated electrode at m different surface densities is first determined. Next, based on the optimal amount of conductive agent in a single-layer coated electrode at different surface densities, a functional relationship can be obtained with the surface 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 multi-layer coated electrode, the sum of the surface 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 dependent variable B obtained is the amount of conductive agent in the active material layer. The embodiment of the present application realizes the accurate quantification of the amount of conductive agent in each layer of the multi-layer coated electrode. The method is simple, practical and feasible, filling the gap in determining the amount of conductive agent in each layer of the multi-layer coated electrode. In addition, the embodiment of the present application also takes into account that the closer the active material layer is to the current collector, the greater the theoretical maximum amount of charge that can pass through it. Therefore, by taking the sum of the surface density of the active material layer and all active material layers located on the surface of the active material layer away from the current collector as the independent variable G in the functional relationship, and taking 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 is gradually reduced from the active material layer close to the current collector to the active material layer away from the current collector, thereby maintaining a low internal resistance of the battery while also helping to improve the energy density of the battery.

[0030] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0032] Figure 1 A flow chart of a method for determining the amount of conductive agent used in each layer of a multi-layer coated electrode provided in an embodiment of the present application;

[0033] Figure 2A flow chart of another method for determining the amount of conductive agent used in each layer of a multi-layer coated electrode provided in an embodiment of the present application;

[0034] Figure 3 A schematic cross-sectional view of a multi-layer coated electrode provided in an embodiment of the present application;

[0035] Figure 4 This is a fitting curve between the optimal amount of conductive agent in a single-layer coated electrode and the surface density of the single-layer coated electrode constructed based on the optimal amount of conductive agent in a single-layer coated electrode at different surface densities in the embodiment of the present application. DETAILED DESCRIPTION

[0036] In order to make the technical solutions and beneficial effects of the present invention more clearly understood, the following is a detailed description of the invention by referring to the accompanying drawings and listing specific embodiments. It should be understood that these embodiments are intended only to illustrate the present invention and are not intended to limit the scope of the invention. The experimental methods in the following examples where specific conditions are not specified are generally based on conventional experimental conditions. Unless otherwise specified, the reagents and raw materials used in the present invention are commercially available.

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

[0038] The purpose of the terms used herein is only to describe specific embodiments and is not intended to limit the present application. When used herein, the singular forms "a", "an", and "the" are 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, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0039] In order to fully understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solution of the present application. The preferred embodiments of the present application are described in detail below. However, in addition to these detailed descriptions, the present application may also have other implementation methods.

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

[0041] In the following examples, if no specific techniques or conditions are specified, the methods are generally carried out according to conventional techniques or conditions described in the literature in the field, or according to the product instructions and the conditions recommended by the manufacturer. The numerical ranges in the following examples are all inclusive.

[0042] The present application provides a method for determining the amount of conductive agent in each layer of a multi-layer coated electrode. The multi-layer coated electrode comprises a current collector and a plurality of active material layers sequentially stacked on at least one side of the current collector. Figure 1 The method for determining the amount of conductive agent in each layer of a multi-layer coated electrode provided in an embodiment of the present application includes the following steps:

[0043] S1: Determine the optimal amount of conductive agent in m single-layer coated electrodes at different surface densities, where the single-layer coated electrode includes a single layer of active material. For each single-layer coated electrode, the method for determining the optimal amount includes:

[0044] Prepare n single-layer coated electrode sheets to be tested with equal surface density and different amounts of conductive agent, make batteries with each of the single-layer coated electrode sheets to be tested, and measure the internal resistance of the batteries. Use the conductive agent amount of the single-layer coated electrode sheet to be tested as the independent variable x and the internal resistance of the corresponding battery as the dependent variable y to obtain a fitting curve. The minimum x value corresponding to the absolute value of the slope of the fitting curve reaching a preset slope value is determined as the optimal amount of the conductive agent in the single-layer coated electrode sheet;

[0045] S2: Based on the optimal amount of conductive agent in the single-layer coated electrode at different surface densities, a fitting curve is constructed between the optimal amount of conductive agent in the single-layer coated electrode and the surface density of the single-layer coated electrode, and a functional relationship is obtained with the surface density as the independent variable G and the amount of conductive agent as the dependent variable B;

[0046] S3: For each active material layer in the multi-layer coated electrode, the sum of the surface density 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.

[0047] The embodiment of the present application realizes the accurate quantification of the amount of conductive agent in each layer of the multi-layer coated electrode. The method is simple, practical and feasible, filling the gap in determining the amount of conductive agent in each layer of the multi-layer coated electrode. In addition, the embodiment of the present application also takes into account that the closer the active material layer is to the current collector, the greater the theoretical maximum amount of charge that can pass through it. Therefore, by taking the sum of the surface density of the active material layer and all active material layers located on the surface of the active material layer away from the current collector as the independent variable G in the functional relationship, and taking 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 is gradually reduced from the active material layer close to the current collector to the active material layer away from the current collector, thereby maintaining a low internal resistance of the battery while also helping to improve the energy density of the battery.

[0048] In step S1, making n single-layer coated electrodes to be tested with equal surface density and different conductive agent dosages can include: increasing the conductive agent dosage in the n single-layer coated electrodes to be tested from a first preset value to a second preset value in sequence; wherein the single increase in the conductive agent dosage 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 the single-layer coated electrode can be the mass proportion 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 active material (also referred to as main material), conductive agent and other additives (specifically, for example, including binder), wherein the mass proportions of main material, conductive agent and other additives in the active material layer are represented by A%, B% and C%, respectively, and A+B+C=100. From the first single-layer coated electrode to be tested to the nth single-layer coated electrode to be tested, the amount of conductive agent B% increases from the first preset value B0% to the second preset value B n %, the amount of other additives C% remains unchanged, and the amount of main material A% is adjusted accordingly. For example, the amount of conductive agent is increased, and the amount of main material is correspondingly reduced to maintain A+B+C=100, so that the surface density of n single-layer coated electrodes to be tested is equal. Exemplarily, 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, for example, includes at least one of a ternary positive electrode material, lithium iron phosphate material, lithium cobalt oxide, and lithium nickel oxide, and the negative electrode active material, for example, includes 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 the embodiment of the present application, from the first single-layer coated electrode to be tested to the nth single-layer coated electrode to be tested, the amount of conductive agent B% increases from the first preset value B0% to the second preset value B n%, 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, so that at least three conductive agent dosage points can be set between the first preset value and the second preset value, so that n can be greater than or equal to 5, which is beneficial to improve the accuracy of the optimal amount of conductive agent in the subsequent single-layer coated electrode.

[0051] Furthermore, in some specific embodiments, the single increase in the amount of the conductive agent from the first single-layer coated electrode piece to be tested to the nth single-layer coated electrode piece to be tested 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%. In this way, the value of n can be increased, that is, the gradient of the conductive agent amount can be further increased, which is conducive to further improving the accuracy of the optimal amount of conductive agent in the subsequently obtained single-layer coated electrode piece.

[0052] In some specific embodiments, the single increment value may be a fixed value, which can increase the uniformity of the change in the amount of the conductive agent in the n single-layer coated electrode sheets to be tested, thereby further improving the accuracy of the subsequently obtained optimal amount of the conductive agent in the single-layer coated electrode sheet.

[0053] The first preset value and the second preset value can be adjusted according to the type of single-layer coated electrode. For single-layer coated electrode with a smaller surface density (also called thin-coated electrode), the appropriate amount of conductive agent is usually relatively small. In this case, the first preset value needs to be small enough; and for single-layer coated electrode with a larger surface density (also called thick-coated electrode), the appropriate amount of conductive agent is usually relatively large. In this case, the second preset value needs to be large enough. This is conducive to obtaining the accurate optimal amount of conductive agent in the 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 % can be greater than or equal to 3%, preferably greater than or equal to 5%. In this way, the needs of both thin-coated and thick-coated electrodes can be taken into account, and the scope of application is wider. 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] For a single-layer thin-coated electrode and a single-layer thick-coated electrode, the difference in the amount of conductive agent used is relatively large. Therefore, in some other embodiments, the first preset value B0% and the second preset value Bn % can be adjusted accordingly, for example, for surface density ≤ 5mg / cm 2 The first preset value B0% can be 0%, and the second preset value B n % can be 1%; for surface density ≥8mg / cm 2 The first preset value B0% can be 3%, and the second preset value B n % can be 5%. This can reduce the number n of single-layer coated electrodes to be prepared, not only to obtain the accurate optimal amount of conductive agent, but also to simplify the preparation process and improve efficiency.

[0056] After preparing n single-layer coated electrodes to be tested with equal surface density and different amounts of conductive agent, each single-layer coated electrode to be tested is made into a battery and the internal resistance of the battery is tested. It should be noted here that if the n single-layer coated electrodes to be tested are positive electrodes, the same negative electrode is used to prepare the corresponding n batteries, that is, the amount of conductive agent in all negative electrodes remains the same. On the contrary, if the n single-layer coated electrodes to be tested are negative electrodes, the same positive electrode is used to prepare the corresponding n batteries, that is, the amount of conductive agent in all positive electrodes remains the same. In addition, the types of main materials, conductive agents and other additives in the n single-layer coated electrodes to be tested can be the same; in this way, the influence of the test results of the internal resistance of the battery due to the different types of at least one of the main materials, conductive agents and other additives in different single-layer coated electrodes to be tested can be avoided, which is conducive to obtaining the accurate 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 sheet, the negative electrode sheet and the battery are not limited in the embodiments of the present application, and they can be prepared by methods well known to those skilled in the art.

[0058] Specifically, the battery internal resistance test method may be, for example, as follows: at 25°C, 50% SOC (State of Charge), discharge at a rate of 2C for 30 seconds, and internal resistance DCR = (pre-discharge voltage V1 - post-discharge voltage V2) / discharge current I. Of course, this application does not exclude the use of other test methods to test the battery internal resistance.

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

[0060] It can be understood that as the amount of conductive agent in the single-layer coated electrode to be tested 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 in the amount of conductive agent. Therefore, in the above-mentioned 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 to be the optimal amount of the conductive agent. In the embodiment of the present application, the inflection point of the fitting curve can be more accurately located by the change in the absolute value of the slope of the fitting curve. Specifically, the minimum x value corresponding to when the absolute value of the slope of the fitting curve reaches a preset slope value can be determined as the optimal amount of the conductive agent in the single-layer coated electrode. The smaller the preset slope value here, the more accurately the optimal amount of the conductive agent is determined. In some specific embodiments, the preset slope value can be less than or equal to 5% of the maximum absolute value of the slope of the fitting curve, preferably less than or equal to 3% of the maximum absolute value of the slope of the fitting curve, and further preferably 0.

[0061] In some embodiments, in step S1, m ≥ 3. That is, the optimal amount of the conductive agent in the single-layer coated electrode sheet at at least three different surface densities is determined. In this way, the functional relationship obtained in step S2 with the surface density as the independent variable G and the conductive agent amount as the dependent variable B based on the optimal amount of the conductive agent in the single-layer coated electrode sheet at different surface densities will be more accurate.

[0062] The following takes m=3 as an example to introduce the specific steps of executing the above steps S1 and S2.

[0063] First, execute step S1 to determine the optimal amount of conductive agent in the single-layer coated electrode at three surface densities. The details are as follows:

[0064] 1) At a surface density of G1, n1 single-layer coated electrodes to be tested with equal surface density and different amounts of conductive agent are prepared. From the first single-layer coated electrode to be tested to the n1th single-layer coated electrode to be tested, the mass proportion B% of the conductive agent increases from 0% to 3%, and a gradient is set every 0.3% (i.e., n1=11). The mass proportion C% of other additives remains unchanged, and the mass proportion A% of the main material is adjusted accordingly to maintain A+B+C=100; the n1 single-layer coated electrodes to be tested are prepared into batteries, and the internal resistance DCR of each battery is measured; the amount of conductive agent of each single-layer coated electrode to be tested is used as the independent variable x, and the internal resistance of the corresponding battery is used as the dependent variable y, and a fitting curve is obtained by fitting. The minimum x value corresponding to the absolute value of the slope of the fitting curve reaching the preset slope value (for example, close to 0) is determined as the optimal amount B1% of the conductive agent in the single-layer coated electrode with a surface density of G1.

[0065] 2) At a surface density of G2, n2 single-layer coated electrodes to be tested with equal surface density and different amounts of conductive agent are prepared. From the first single-layer coated electrode to be tested to the n2 single-layer coated electrode to be tested, the mass proportion B% of the conductive agent increases from 0% to 3%, and a gradient is set every 0.3% (i.e., n2=11). The mass proportion C% of other additives remains unchanged, and the mass proportion A% of the main material is adjusted accordingly to maintain A+B+C=100; the n2 single-layer coated electrodes to be tested are prepared into batteries, and the internal resistance DCR of each battery is measured; the amount of conductive agent of each single-layer coated electrode to be tested is used as the independent variable x, and the internal resistance of the corresponding battery is used as the dependent variable y, and a fitting curve is obtained by fitting. The minimum x value corresponding to the absolute value of the slope of the fitting curve reaching the preset slope value (for example, close to 0) is determined as the optimal amount B2% of the conductive agent in the single-layer coated electrode with a surface density of G2.

[0066] 3) At a surface density of G3, n3 single-layer coated electrodes to be tested with equal surface density and different amounts of conductive agent are prepared. From the first single-layer coated electrode to be tested to the n3 single-layer coated electrode to be tested, the mass proportion B% of the conductive agent increases from 0% to 3%, and a gradient is set every 0.3% (i.e., n3=11). The mass proportion C% of other additives remains unchanged, and the mass proportion A% of the main material is adjusted accordingly to maintain A+B+C=100; the n3 single-layer coated electrodes to be tested are prepared into batteries, and the internal resistance DCR of each battery is measured; the amount of conductive agent of each single-layer coated electrode to be tested is used as the independent variable x, and the internal resistance of the corresponding battery is used as the dependent variable y, and a fitting curve is obtained by fitting. The minimum x value corresponding to the absolute value of the slope of the fitting curve reaching the preset slope value (for example, close to 0) is determined as the optimal amount B3% of the conductive agent in the single-layer coated electrode with a surface density of G3.

[0067] Next, execute step S2, and based on the optimal amount of conductive agent in the single-layer coated electrode at different surface densities, construct a fitting curve between the optimal amount of conductive agent in the single-layer coated electrode and the surface density of the single-layer coated electrode, and obtain a functional relationship with the surface density as the independent variable G and the amount of conductive agent as the dependent variable B.

[0068] Specifically, according to the data groups (G1, B1), (G2, B2), (G3, B3) of the optimal dosage of the conductive agent in the single-layer coated electrode at different surface densities obtained in step S1, this data is fitted with a functional relationship B=F(G) with G as the independent variable and B as the dependent variable.

[0069] The above is just an example of 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 groups are obtained in step S1, and the higher the accuracy of the functional relationship obtained by fitting 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 multi-layer coated electrode may further include the step of detecting the accuracy of the functional relationship:

[0071] S21. Determine the amount of a first conductive agent at a certain surface density according to the functional relationship to produce a first test single-layer coated electrode piece; maintain the surface density unchanged, reduce the amount of the conductive agent based on the first amount of the conductive agent, and produce a second test single-layer coated electrode piece; maintain the surface density unchanged, increase the amount of the conductive agent based on the first amount of the conductive agent, and produce a third test single-layer coated electrode piece; the absolute value of the difference between the amount of the conductive agent in the second test single-layer coated electrode piece and the third test single-layer coated electrode piece and the amount of the first conductive agent is less than the minimum difference in the amount of the conductive agent in different single-layer coated electrode pieces to be tested in step S1;

[0072] Specifically, any surface density g1 can be substituted into the functional relationship B=F(G) obtained in step S2 to obtain the first conductive agent dosage b1%, and then the first test single-layer coated electrode is made with the main material mass proportion A%, the first conductive agent mass proportion b1, and the other additives mass proportion C%; the second test single-layer coated electrode is made with the main material mass proportion (A%-0.2%), the conductive agent mass proportion (b1+0.2%), and the other additives mass proportion C%; the third test single-layer coated electrode is made with the main material mass proportion (A%+0.2%), the conductive agent mass proportion (b1-0.2%), and the other additives mass proportion C%.

[0073] It should be noted that the above-mentioned reduction and increase of 0.2% in the amount of conductive agent in the second test single-layer coated electrode and the third test single-layer coated electrode relative to the amount of the first conductive agent is only an example. This is based on the above embodiment. In step S1, when the surface density is G1, G2 and G3, the minimum increase gradient of the conductive agent amount in the multiple single-layer coated electrode sheets to be tested at each surface density is 0.3%. In actual applications, the absolute value of the difference between the amount of conductive agent in the second test single-layer coated electrode and the third test single-layer coated electrode and the amount of the first conductive agent can be less than the minimum difference in the amount of conductive agent in different single-layer coated electrode sheets to be tested in step S1. This can better ensure the reliability of the accuracy detection of the functional relationship.

[0074] S22, respectively fabricating the first test single-layer coated electrode piece, the second test single-layer coated electrode piece, and the third test single-layer coated electrode piece into a first battery, a second battery, and a third battery, and testing the internal resistance of each battery;

[0075] The battery internal resistance test method can be understood by referring to the battery internal resistance test method described in the above embodiment, which will not be repeated here. The internal resistance of the first battery, the second battery and the third battery can be recorded 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 a 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;

[0077] 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.

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

[0079] The relative difference between DCR2 and DCR1, and the relative difference between DCR3 and DCR1, represent the percentage by which the smaller of the two decreases relative to the larger. For example, if DCR2 ≥ DCR1, the relative difference between the second internal resistance and the first internal resistance = ((DCR2 - DCR1) / DCR2) * 100%. If 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 may be less than or equal to 5%. That is, when the relative difference between DCR1 and DCR3 is within 5%, DCR1 and DCR3 may be considered to be substantially equal. The first preset difference is greater than the second preset difference, and the first preset difference is greater than 5%. The first preset difference may be, for example, 10%, 20%, 30%, 40%, 50%, or a greater value, and may be determined based on the difference in the amount of conductive agent used in the first test single-layer coated electrode and the second test single-layer coated electrode.

[0081] In the embodiment of the present application, a step is added to test 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, that is, by adding more surface density gradients in step S1, to obtain a more accurate functional relationship B=F(G) in step S2. If the functional relationship obtained after the first increase in the value of m still does not meet the accuracy requirement after testing, the value of m can be further increased and the functional relationship can be obtained again until the accuracy requirement is met.

[0082] Finally, step S3 is performed. For each active material layer in the multi-layer coated electrode, the sum of the surface density 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.

[0083] Please refer to Figure 3 The multilayer coated electrode sheet 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 closer to the current collector to farther away from it, the multilayer active material layers 200 sequentially include a first active material layer 201, ..., and an Nth active material layer 204 (N is greater than or equal to 2). The active material layers contain active materials. The current generated by the active materials during charge and discharge is collected by the current collector and then output to the external circuit. That is, the current generated by the active materials in the upper active material layer farther away from the current collector during charge and discharge must pass through the lower active material layer closer to the current collector before reaching the current collector for collection. For example, if the capacity of each active material layer in the multilayer active material layer 200 is C, then the theoretical maximum charge that can be passed through the Nth active material layer 204 is C, the theoretical maximum charge that can be passed through the N-1th active material layer is 2C, and so on. The theoretical maximum charge that can be passed through the second active material layer is (N-1)C, and the theoretical maximum charge that can be passed through the first active material layer 201 is nC. That is, the closer the active material layer is to the current collector, the greater the theoretical maximum charge that can pass through it. Therefore, the closer the active material layer is to the current collector, the higher the amount of conductive agent required. 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 the embodiment of the present application, for each active material layer in the multi-layer coated electrode, the sum of the surface density 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 the active material layer. In this way, the amount of conductive agent determined in each active material layer in the multi-layer coated electrode is gradually reduced, which not only better ensures the conductivity of the multi-layer 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 refer to Figure 3 Taking N greater than or equal to 4 as an example, the surface densities of the first active material layer 201 to the Nth active material layer 204 are respectively recorded 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 B2'=F(G2'+G3'+...+G N '), the amount of conductive agent in the third active material layer 203 B3'=F(G3'+...+G N '), and so on, the amount of conductive agent in the Nth active material layer 204 is B N '=F(G N ').

[0085] The present application also provides an embodiment of the method for determining the amount of conductive agent used in each layer of a multi-layer coated electrode sheet, as described in any of the above embodiments, for use in electrode sheet production. The electrode sheet herein may include a positive electrode sheet and / or a negative electrode sheet. In other words, the method for determining the amount of conductive agent used in each layer of a multi-layer coated electrode sheet in the present application embodiment is applicable to both multi-layer coated positive and negative electrode sheets, and thus has high practical application value.

[0086] The following uses the application of the method for determining the amount of conductive agent in each layer of a multi-layer coated electrode in the preparation of a negative electrode as an example to further illustrate the technical solution of the present 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 proportions 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 compacted density of the negative electrode sheet is 1.6 g / cc. The positive and negative electrode N / P ratio (the ratio of the negative electrode capacity to the positive electrode capacity) is 1.12.

[0088] The batteries use the same positive electrode sheet. The active material layer comprises a six-series ternary cathode material (main cathode material), a binder called PVDF, conductive carbon black SP (conductive agent), and carbon nanotubes (CNTs). The weight percentages of the six-series ternary cathode material, PVDF, conductive carbon black, and CNTs in the active material layer are 90%, 2%, 4%, and 4%, respectively. The compacted density of the positive electrode sheet is 3.45g / cc.

[0089] First, the surface density is 8mg / cm2 、10mg / cm 2 , 12mg / cm 2 When the surface density is 1, 11 single-layer coated negative electrode sheets with the same surface density and different amounts of conductive agent are prepared. The formulas 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 surface density of each single-layer coated negative electrode sheet in Table 1 is 8 mg / cm 2 The surface density of each single-layer coated negative electrode sheet to be tested in Table 2 is 10 mg / cm 2 The surface density of each single-layer coated negative electrode sheet to be tested in Table 3 is 12 mg / cm 2 .

[0090] Next, batteries were fabricated by combining the single-layer coated negative electrode sheets (tested at different areal densities) with the aforementioned positive electrode sheets. The batteries were discharged at a 2C rate for 30 seconds at 25°C and 50% SOC. The internal resistance (DCR) of the batteries was measured, where DCR = (pre-discharge voltage V1 - post-discharge voltage V2) / discharge current I. The internal resistance test results for the batteries corresponding to the single-layer coated negative electrode sheets tested are shown in Tables 1 to 3.

[0091] Table 1 Surface density is 8 mg / cm 2 When the formula of each single-layer coated negative electrode sheet to be tested and the internal resistance of the corresponding battery

[0092]

[0093]

[0094] Table 2 Surface density is 10 mg / cm 2 When the formula of each single-layer coated negative electrode sheet to be tested and the internal resistance of the corresponding battery

[0095] Serial number Graphite content A% SP content B% CMC content SBR content DCR / mΩ 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 Surface density is 12 mg / cm 2 When the formula of each single-layer coated negative electrode sheet to be tested and the internal resistance of the corresponding battery

[0097] Serial number Graphite content A% SP content B% CMC content SBR content DCR / mΩ 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, according to the test data in Tables 1 to 3, for the 11 single-layer coated negative electrode sheets to be tested at each surface density, the SP content (conductive agent dosage) of each single-layer coated electrode sheet to be tested is used as the independent variable x, and the internal resistance of the corresponding battery is used as the dependent variable y, and a fitting curve is obtained. The minimum x value corresponding to the absolute value of the slope of the fitting curve reaching the preset slope value (close to 0) is determined as the optimal dosage of the conductive agent in the single-layer coated electrode sheet of the surface density. For the surface density of 8mg / cm 2For the single-layer coated electrode with a surface density of 10 mg / cm2, the optimal amount of conductive agent is 0.9% as shown in Table 1. For the single-layer coated electrode with a surface density of 12 mg / cm2, the optimal amount of conductive agent is 2.1% as shown in Table 3.

[0099] Next, (8, 0.9), (10, 1.5) and (12, 2.1) are used to fit the functional relationship B = F (G) with the surface density G as the independent variable and the conductive agent dosage B as the dependent variable. The fitting results are shown in Figure 2. Figure 4 As shown, the fitted functional relationship is B=0.3G-1.5, where the unit of G is mg / cm2 and the unit of B is %. After substituting the surface density in mg / cm2 into the formula, the unit of B is %, that is, the amount of conductive agent obtained is expressed by the mass proportion of the conductive agent in the active material layer.

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

[0101] Specifically, firstly the surface density is 9 mg / cm 2 Substituting into the functional relationship B=0.3G-1.5, it is obtained that the amount of conductive agent is 1.2%. The amount of conductive agent 1.2% 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, and 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 described in the above steps to make a battery, and the internal resistance of each battery is tested according to the same method as in the above steps.

[0102] ① In the first test single-layer coated electrode, 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 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 tested single-layer coated electrode, the content of the main graphite material is 96.1%, the content of the conductive agent SP 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 tested single-layer coated electrode is 32.6mΩ.

[0105] According to the above test results, the relative difference between DCR3 and DCR1 = ((DCR1-DCR3) / DCR1)*100%=2.7%, that is, the second preset difference is less than or equal to 5%. The relative difference between DCR2 and DCR1 = ((DCR2-DCR1) / DCR2)*100%=43.6%, that is, the first preset difference is greater than the second preset difference. Therefore, the test results of the internal resistance of the above three batteries satisfy DCR2>DCR1≈DCR3, which indicates that the accuracy of the functional relationship B=0.3G-1.5 obtained in the previous step meets the requirements.

[0106] Finally, determine the amount of conductive agent used in each layer of the multi-layer coated electrode. Take the 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 on the surface of the current collector in sequence. The surface density of the first active material layer to the third active material layer is 2 mg / cm 2 , 4mg / cm 2 and 8mg / cm 2 Based on the functional relationship B = 0.3G-1.5, it can be determined that the amount of conductive agent in the first active material layer = 0.3*(2+4+8)-1.5 = 2.7%; the amount of conductive agent in the second active material layer = 0.3*(4+8)-1.5 = 2.1%; and the amount of conductive agent in the third active material layer = 0.3*8-1.5 = 0.9%.

[0107] After determining the amount of conductive agent (SP) used in each active material layer of the three-layer coated negative electrode sheet, battery examples and comparative examples were prepared. The coating type, surface density, and active material layer formulations of the negative electrode sheets of the battery examples and the comparative example are shown in Table 4 below. The negative electrode active material used in the negative electrode sheets of the battery examples and the comparative example was graphite, the conductive agent was SP, and the binder was a combination of CMC and SBR. The positive electrode sheets of the battery examples and the comparative example both used the positive electrode sheets described in the above steps. The positive and negative electrode sheets were assembled to obtain batteries.

[0108] Table 4

[0109]

[0110]

[0111] The internal resistance and energy density of the batteries in the battery examples and the battery comparison examples were tested. The internal resistance test method of the battery is the same as the battery internal resistance test method in the above steps. The battery energy density test method is as follows: first, the battery is allowed to stand at 25°C for 30 minutes; next, it is charged to 4.2V at a constant current rate of 1C, and then charged at a constant voltage to a cutoff current of 0.05C; next, after standing for 30 minutes, it is discharged to 2.8V at a rate of 1C, and the total discharge energy of the discharge process is recorded as W. The battery cell is weighed, and the weight of the battery cell is recorded as G; the energy density of the battery = W / G. The test results are shown in Table 5.

[0112] Table 5

[0113]

[0114] From the data in Table 5, it can be seen that when the sum of the surface densities of the three active material layers in the three-layer coated negative electrode sheet is the same as the surface density of the single active material layer in the single-layer coated negative electrode sheet, the difference between the internal resistance DCR of the battery corresponding to the three-layer coated negative electrode sheet and the internal resistance DCR of the battery corresponding to the single-layer coated negative electrode sheet is about 0.27%, which can be considered to be basically the same, and the energy density of the battery corresponding to the three-layer coated negative electrode sheet is increased by 1.28% relative to the energy density of the battery corresponding to the single-layer coated negative electrode sheet. It can be seen from this that the method for determining the amount of conductive agent in each layer of the multi-layer coated electrode provided in this application, from the active material layer close to the current collector to the active material layer farthest from the current collector, gradually reduces the amount of conductive agent in each active material layer. Under the condition of the same surface density, it not only maintains the battery internal resistance similar to that of the single-layer coating, but also improves the battery energy density. Although the value of the battery energy density improvement is relatively small, since the amount of conductive agent in the active material layer itself is very small, the relative benefit is very high, and it can be considered to have a significant effect on the improvement of the battery energy density. Moreover, the method for determining the amount of conductive agent used in each layer of a multi-layer coated electrode provided in this application has more obvious advantages in multi-layer thick-coated electrodes.

[0115] The present invention provides a method for quantitatively determining the amount of conductive agent in each layer of a multi-layer coated electrode, provides a clear and quantitative definition of the amount of conductive agent in each layer of a multi-layer coated electrode, fills the gap in the definition of the amount of conductive agent in each layer of a multi-layer coated electrode, and can improve the energy density and dynamic performance of the battery while ensuring the conductivity of the multi-layer coated electrode.

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

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

Claims

1. A method for determining the amount of conductive agent in each layer of a multi-layer coated electrode, characterized in that: The multi-layer coated electrode comprises a current collector and a plurality of active material layers sequentially stacked on at least one side surface of the current collector; the method comprises the following steps: S1: Determine the optimal amount of conductive agent in m single-layer coated electrode sheets at different surface densities, wherein the single-layer coated electrode sheet includes a single layer of active material layer; for each single-layer coated electrode sheet, the method for determining the optimal amount includes: Prepare n single-layer coated electrode sheets to be tested with equal surface density and different amounts of conductive agent, make each of the single-layer coated electrode sheets to be tested into a battery and measure the internal resistance of the battery, use the conductive agent amount of the single-layer coated electrode sheet to be tested as the independent variable x, and the internal resistance of the corresponding battery as the dependent variable y to obtain a fitting curve, and determine the minimum x value corresponding to the absolute value of the slope of the fitting curve reaching a preset slope value as the optimal amount of conductive agent in the single-layer coated electrode sheet; S2: Based on the optimal amount of conductive agent in the single-layer coated electrode at different surface densities, a fitting curve is constructed between the optimal amount of conductive agent in the single-layer coated electrode and the surface density of the single-layer coated electrode, and a functional relationship is obtained with the surface density as the independent variable G and the amount of conductive agent as the dependent variable B; S3: For each active material layer in the multi-layer coated electrode, the sum of the surface density 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.

2. The method for determining the amount of conductive agent in each layer of a multi-layer coated electrode according to claim 1, characterized in that: In step S1, m≥3.

3. The method for determining the amount of conductive agent in each layer of a multi-layer 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 fitting curve, and is preferably 0.

4. The method for determining the amount of conductive agent in each layer of a multi-layer coated electrode according to claim 1, characterized in that: In step S1, n single-layer coated electrodes to be tested are prepared with equal surface density and different amounts of conductive agent, 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 a multi-layer 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, preferably 10%.

6. The method for determining the amount of conductive agent in each layer of a multi-layer coated electrode according to claim 4, characterized in that: The single increase value is a fixed value.

7. The method for determining the amount of conductive agent in each layer of a multi-layer coated electrode according to claim 4, characterized in that: The amount of conductive agent in the single-layer coated electrode is the mass proportion of the conductive agent in the single-layer 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%.

8. The method for determining the amount of conductive agent in each layer of a multi-layer coated electrode according to any one of claims 4 to 7, characterized in that: After step S2, the method further includes the following steps: S21, obtaining the amount of the first conductive agent at a certain surface density according to the functional relationship, and producing a first test single-layer coated electrode; Keeping the surface density unchanged, the amount of conductive agent is reduced on the basis of the first amount of conductive agent, and a second test single-layer coated electrode piece is produced; keeping the surface density unchanged, the amount of conductive agent is increased on the basis of the first amount of conductive agent, and a third test single-layer coated electrode piece is produced; The absolute values ​​of the differences between the amounts of the conductive agent in the second test single-layer coated electrode piece and the third test single-layer coated electrode piece and the amount of the first conductive agent are both smaller than the minimum difference in the amounts of the conductive agent in different single-layer coated electrode pieces to be tested in step S1; S22, fabricating the first test single-layer coated electrode piece, the second test single-layer coated electrode piece, and the third test single-layer coated electrode piece into a first battery, a second battery, and a third battery, respectively, and testing the internal resistance of each battery; S23. Determine whether a first internal resistance of the first battery, a second internal resistance of the second battery, and a third internal resistance of the third battery meet the following conditions: the second internal resistance is greater than the first internal resistance, and a relative difference between the second internal resistance and the first internal resistance is greater than or equal to a first preset difference, and a 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, the value of m in step S1 is increased, and the functional relationship is obtained again according to steps S1 and S2.

9. The method for determining the amount of conductive agent in each layer of a multi-layer coated electrode according to claim 8, characterized in that: The second preset difference is less than or equal to 5%.

10. Use of the method for determining the amount of conductive agent in each layer of a multi-layer coated electrode according to any one of claims 1 to 9 in preparing an electrode; optionally, the electrode comprises a positive electrode and / or a negative electrode.

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