Method for determining particle size distribution of primary particles of electrode active material and application thereof

Abstract

The present application relates to a method for determining the particle size distribution of primary particles of an electrode active material and the application thereof. The determination method comprises the following steps: photographing a cross section or surface of an active layer of an electrode sheet, so as to obtain a plurality of images, wherein the active layer contains an electrode active material; measuring the particle sizes of primary particles of the electrode active material in the plurality of images; on the basis of the particle sizes of the primary particles of the electrode active material, calculating the number statistical value of primary particles in the entire particle size range; and calculating the number and proportion statistical values of primary particles in different particle size ranges, so as to obtain the particle size distribution of the primary particles of the electrode active material. The test error of the determination method is small, and the accuracy of the obtained particle size distribution of primary particles of an electrode active material is higher.

Description

Methods and applications for determining the primary particle size distribution of electrode active materials

[0001] Cross-referencing

[0002] This application claims priority to Chinese Patent Application No. 202411654086.X, filed on November 19, 2024, entitled "Method and Application for Determination of Primary Particle Size Distribution of Electrode Active Materials", which is incorporated herein by reference in its entirety. Technical Field

[0003] This application relates to the field of secondary battery technology, and in particular to a method for determining the particle size distribution of primary particles in an electrode active material and its application. Background Technology

[0004] In recent years, with the increasingly widespread application of secondary batteries such as lithium-ion batteries, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant development of lithium-ion batteries, higher requirements have been placed on their rate performance, cycle performance, and safety performance.

[0005] Electrode active materials are a crucial component of lithium-ion batteries, and the primary particle size distribution of these materials typically influences the battery's electrical properties, such as DC internal resistance (DCR) and rate performance. However, traditional methods for measuring the primary particle size of positive electrode active materials are not accurate enough. Consequently, attempts to improve the electrical performance of secondary batteries by adjusting the primary particle size distribution of the active material often fail to yield the desired performance. Summary of the Invention

[0006] This application provides a method and application for determining the primary particle size distribution of an electrode active material. The method has a small testing error and the obtained primary particle size distribution of the electrode active material is more accurate.

[0007] A first aspect of this application provides a method for determining the primary particle size distribution of an electrode active material, comprising the following steps:

[0008] Multiple images are obtained by photographing the cross-section or surface of the active layer of the electrode; the active layer contains the electrode active material;

[0009] The particle size of the primary particles of the electrode active material in multiple images was measured.

[0010] Based on the particle size of the primary particles of the electrode active material, calculate the statistical value of the number of primary particles across the entire particle size range;

[0011] The number and proportion of primary particles in different particle size ranges are calculated to obtain the particle size distribution of the primary particles in the electrode active material.

[0012] The above measurement method obtains the primary particle size distribution of the electrode active material by measuring the electrode active material in the electrode sheet. This can reduce the agglomeration and stacking of the electrode active material. The primary particles of the electrode active material in the image are basically at the same horizontal position in the same field of view, which can reduce the interference of imaging depth of field and is conducive to obtaining the actual primary particle size of the electrode active material. In this way, the test error of the primary particle size distribution of the electrode active material is relatively small and the accuracy is higher.

[0013] In some embodiments, the active layer does not contain a conductive agent. This reduces the interference of the conductive agent on the primary particles of the electrode active material, reduces testing errors, and further improves the accuracy of the particle size distribution of the primary particles of the electrode active material.

[0014] In some embodiments, the step of photographing a cross-section or surface of the active layer of the electrode includes:

[0015] Use SEM to photograph the cross-section or surface of the active layer of the electrode.

[0016] The images obtained using SEM show clearer boundaries between the primary particles of the electrode active material, resulting in smaller errors and higher accuracy in the testing of the primary particle size distribution of the electrode active material.

[0017] In some embodiments, the step of measuring the particle size of the primary particles of the electrode active material in multiple images includes:

[0018] Obtain the circumscribed rectangle of the primary particles of the electrode active material in the image. Calculate the particle size L1 of the primary particles of the electrode active material based on the diagonal length of the circumscribed rectangle. L1 satisfies the following: Where L2 is the length of the diagonal of the circumscribed rectangle.

[0019] This can improve the accuracy of measuring the primary particle size distribution of the electrode active material.

[0020] In some embodiments, the number of images at the same magnification is 10 to 50. This reduces the problem of unrepresentative primary particle size distribution due to an insufficient number of images, thereby further improving the accuracy of the primary particle size distribution of the electrode active material measured by the above method.

[0021] In some embodiments, the method for preparing the electrode sheet includes the following steps: depositing an electrode slurry containing the electrode active material and a binder on at least one surface of a substrate, and sequentially subjecting it to drying and rolling processes to form the active layer, thereby obtaining the electrode sheet. This results in a relatively smooth surface for the electrode sheet, which can further improve the accuracy of the measured primary particle size distribution of the electrode active material.

[0022] In some embodiments, the electrode active material includes a positive electrode active material or a negative electrode active material.

[0023] In some embodiments, the positive electrode active material includes one or more of lithium phosphate and ternary positive electrode materials.

[0024] In some embodiments, the positive electrode active material comprises only lithium phosphate, and the compaction density of the electrode sheet is 2 g / cm³. 3 ~2.6g / cm 3 This reduces the probability of lithium phosphate particles breaking, thereby further improving the accuracy of the primary particle size distribution of the electrode active material measured by the above method.

[0025] In some embodiments, the lithium-containing phosphate includes the chemical formula Li m A a Fe x D d P y E e O z G g The material comprises, wherein A includes at least one element selected from Al, Na, K and Mg; D includes at least one element selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti and V; E includes at least one element selected from B, S, Si and N; G includes at least one element selected from S, F, Cl and Br; 0.5≤m≤1.5, 0≤a≤0.1, 0.5≤x≤1, 0≤d≤0.5, 0.5≤y≤1, 0≤e≤0.5, 3.5≤z≤4, and 0≤g≤0.5.

[0026] In some embodiments, the positive electrode active material comprises only ternary positive electrode material, and the compaction density of the electrode sheet is 3.3 g / cm³. 3 ~3.6g / cm 3 This reduces the probability of ternary cathode material particles breaking, thereby further improving the accuracy of the primary particle size distribution of the electrode active material measured by the above method.

[0027] In some embodiments, the step of calculating the number and percentage statistics of primary particles in different particle size ranges includes: calculating one or more of the following parameters (1) to (17):

[0028] (1) Statistical value of the number of primary particles larger than 3μm;

[0029] (2) Statistical value of the number of primary particles larger than 1 μm;

[0030] (3) Statistical value of the number of primary particles smaller than 100nm;

[0031] (4) Statistical value of the number of primary particles smaller than 150nm;

[0032] (5) Statistical value of the number of primary particles smaller than 200nm;

[0033] (6) The statistical value of the proportion of primary particles larger than 3 μm in the total number of primary particles;

[0034] (7) The statistical value of the proportion of primary particles larger than 1 μm in the total number of primary particles;

[0035] (8) The statistical value of the proportion of primary particles smaller than 100 nm in the primary particles;

[0036] (9) The statistical value of the proportion of primary particles smaller than 150 nm in the primary particles;

[0037] (10) The statistical value of the proportion of primary particles smaller than 200 nm in the primary particles;

[0038] (11) Dn1 of the primary particles;

[0039] (12) Dn2 of the primary particles;

[0040] (13) Dn3 of the primary particles;

[0041] (14) The Dn10 of the primary particles;

[0042] (15) Dn50 of the primary particles;

[0043] (16) The Dn90 of the primary particles;

[0044] (17) The Dn99 of the primary particles.

[0045] By statistically analyzing one or more of the above parameters (1) to (17), it is beneficial to adjust the compaction density of the electrode sheet, or to improve the electrical performance of the secondary battery, such as DCR, rate performance and high-temperature storage.

[0046] In some embodiments, the adhesive includes one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0047] In some embodiments, the substrate material includes one or more of metals and polymers.

[0048] A second aspect of this application provides a method for preparing a secondary battery, including a step of measuring the primary particle size distribution of an electrode active material, wherein the measurement step includes the method for measuring the primary particle size distribution of the electrode active material described in the first aspect of this application.

[0049] A third aspect of this application provides a computer device, the computer device including a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of the measurement method described in the first aspect of this application.

[0050] A fourth aspect of this application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the measurement method described in the first aspect of this application.

[0051] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0052] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0053] Figure 1 is a flowchart of a measurement method according to an embodiment of this application.

[0054] Figure 2 is a SEM image of the electrode prepared in Example 1 at a magnification of 5k. Detailed Implementation

[0055] The following describes in detail, with appropriate reference to the accompanying drawings, some embodiments of the method for determining the primary particle size distribution of the electrode active material of this application and its application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0056] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be combined arbitrarily, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0057] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0058] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0059] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0060] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0061] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0062] Electrode active materials are an important component of lithium-ion batteries. Adjusting the primary particle size distribution of electrode active materials is one of the effective means to improve the electrical performance of secondary batteries. For example, by reducing the primary particle size of electrode active materials, the DCR of secondary batteries can be reduced, thereby improving the rate performance or high-temperature storage performance of secondary batteries.

[0063] Currently, laser particle size analyzers or SEM (scanning electron microscopy) are commonly used to determine the primary particle size distribution of electrode active materials. However, the test results obtained by laser particle size analyzers are usually the particle size distribution of secondary particles or agglomerates, which cannot accurately reflect the primary particle size distribution of the electrode active material. The test results obtained by SEM are also inaccurate because they only reflect a portion of the primary particle size. Therefore, when adjusting the primary particle size distribution of electrode active materials to improve the electrical performance of secondary batteries, the actual primary particle size distribution of the electrode active material differs significantly from the design value due to the inaccuracy of the aforementioned measurement methods. This not only fails to improve the electrical performance of the secondary battery but also causes some electrical performance aspects of the secondary battery to fall short of the design value, resulting in a significant increase in the scrap rate of secondary batteries.

[0064] Based on this, please refer to Figure 1. One embodiment of this application provides a method for determining the primary particle size distribution of an electrode active material, comprising the following steps:

[0065] S100: Takes a cross-section or surface image of the active layer of the electrode to obtain multiple images; the active layer contains electrode active material;

[0066] S200: Measures the particle size of primary particles of electrode active material in multiple images;

[0067] S300: Calculate the statistical value of the number of primary particles across the entire particle size range based on the particle size of the primary particles of the electrode active material;

[0068] S400: Calculate the number and percentage of primary particles in different particle size ranges to obtain the particle size distribution of primary particles in the electrode active material.

[0069] The above measurement method obtains the primary particle size distribution of the electrode active material by measuring the electrode active material in the electrode sheet. This can reduce the agglomeration and stacking of the electrode active material. The primary particles of the electrode active material in the image are basically at the same horizontal position in the same field of view, which can reduce the interference of imaging depth of field and is conducive to obtaining the actual primary particle size of the electrode active material. In this way, the test error of the primary particle size distribution of the electrode active material is relatively small and the accuracy is higher.

[0070] The above-described method can determine the particle size distribution of primary particles of the electrode active material in an electrode sheet, or it can determine the particle size distribution of primary particles of the electrode active material powder. When determining the particle size distribution of primary particles of the electrode active material powder, the electrode active material powder needs to be first prepared into an electrode sheet, and then the determination can be performed using the method described in this application.

[0071] It should be noted that primary particles and secondary particles have meanings known in the art. Primary particles are the basic units constituting a material, the individual particles initially formed during the material synthesis process, without further aggregation or bonding. Secondary particles refer to aggregated particles formed by the aggregation of two or more primary particles.

[0072] In the above measurement method, different particle size ranges are part of the total particle size range. The statistical value of the proportion of primary particles in different particle size ranges can be obtained from the statistical value of the number of primary particles in different particle size ranges and the statistical value of the number of primary particles in the total particle size range. Non-limitingly, the statistical value of the proportion of primary particles in different particle size ranges = (statistical value of primary particles in different particle size ranges / statistical value of primary particles in the total particle size range) × 100%. For example, the statistical value of the proportion of primary particles smaller than 100 nm = (statistical value of primary particles smaller than 100 nm / statistical value of primary particles in the total particle size range) × 100%.

[0073] In this application, when calculating the number of primary particles across the entire particle size range, the number of primary particles across the entire particle size range in a single image can be counted separately, and then the average of multiple images can be calculated to obtain the number of primary particles across the entire particle size range. When calculating the number of primary particles across different particle size ranges, the number of primary particles across different particle size ranges in a single image can be counted separately, and then the average of multiple images can be calculated to obtain the number of primary particles across different particle size ranges.

[0074] Without limitation, when calculating the statistical value of the number of primary particles across the entire particle size range, 30 images at a magnification of 10k can be taken, and the number of primary particles across the entire particle size range in each image can be counted. Then, the average number of primary particles across the entire particle size range in a single image can be calculated and used as the statistical value of the number of primary particles across the entire particle size range. The statistical value of the number of primary particles across the entire particle size range, N0, is calculated as the sum of the number of primary particles across the entire particle size range in the 30 images divided by 30.

[0075] Non-restrictive in calculating the statistical value of the number of primary particles in different particle size ranges, 30 images at a magnification of 10k can be taken, and the number of primary particles in different particle size ranges in each image can be counted. Then, the average number of primary particles in different particle size ranges in a single image can be calculated as the statistical value of the number of primary particles in different particle size ranges. For example, the statistical value of the number of primary particles smaller than 100nm, N1, is the sum of the number of primary particles smaller than 100nm in the 30 images / 30. The statistical value of the proportion of primary particles smaller than 100nm is N1 / N0 × 100%.

[0076] In some embodiments, the active layer does not contain a conductive agent. This reduces the interference of the conductive agent on the primary particles of the electrode active material, reduces testing errors, and further improves the accuracy of the particle size distribution of the primary particles of the electrode active material. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] In some embodiments, the step of photographing the cross-section or surface of the active layer of the electrode includes:

[0078] Use SEM to photograph the cross-section or surface of the active layer of the electrode.

[0079] The images obtained using a scanning electron microscope (SEM) clearly show the boundaries of the primary particles of the electrode active material, thus making the measurement error of the primary particle size distribution of the electrode active material smaller and more accurate.

[0080] Scanning electron microscopes (SEMs) have a secondary electron detector (SED) and a backscattered electron detector (BSD). Using SED or BSD yields different imaging modes; SED provides a secondary electron imaging mode, while BSD provides a backscattered electron imaging mode. In the above embodiments, the SEM's secondary electron imaging mode and / or backscattered electron imaging mode can be used to image the cross-section or surface of the active layer of the electrode.

[0081] Without limitation, when using SEM to photograph the cross-section of the active layer of the electrode, at least one of mechanical cutting, ion beam cutting and focused ion beam (FIB) cutting can be used to cut the cross-section of the active layer of the electrode, and then the prepared cross-section is polished to make the cross-section surface smooth and flat before SEM photography.

[0082] In some embodiments, a cross-section of the active layer of the electrode is captured using the backscattered electron imaging mode of SEM; and / or,

[0083] The surface of the active layer of the electrode is captured using at least one of the secondary electron imaging mode and the backscattered electron imaging mode of SEM.

[0084] This makes the boundaries of the primary particles of the electrode active material in the obtained SEM images clearer, thus resulting in smaller errors and higher accuracy in the statistical analysis of the primary particle size distribution of the electrode active material.

[0085] In some embodiments, the step of measuring the particle size of primary particles of the electrode active material in multiple images includes:

[0086] Obtain the circumscribed rectangle of the primary particles of the electrode active material in the image. Calculate the particle size L1 of the primary particles of the electrode active material based on the length of the diagonal of the circumscribed rectangle. L1 satisfies: Where L2 is the length of the diagonal of the circumscribed rectangle.

[0087] The particle size L1 of the primary particles can be obtained by using the circumscribed rectangle of the primary particles of the electrode active material, which can improve the accuracy of the measured particle size distribution of the primary particles of the electrode active material. This is because large and small particles in the primary particles may stack, and the large particles may be blocked or covered by the small particles. Calculating the particle size L1 of the primary particles using the diagonal length of the circumscribed rectangle of the primary particles can better reflect the true particle size of the primary particles.

[0088] The particle size of large and small particles in a single particle sample can be determined by adjusting the image magnification. For example, at a higher magnification, the particle size of small particles can be determined, while at a lower magnification, the particle size of large particles can be determined. This provides a more accurate estimate of the particle sizes.

[0089] In some embodiments, the number of images at the same magnification is 10 to 50. This reduces the problem of unrepresentative primary particle size distribution due to an insufficient number of images, thereby further improving the accuracy of the primary particle size distribution of the electrode active material measured by the above method. Exemplarily, the number of images at the same magnification includes, but is not limited to, 10, 20, 30, 40, 50 images or any range between the foregoing.

[0090] In some embodiments, the method for preparing the electrode sheet includes the following steps: depositing an electrode slurry containing electrode active material and binder on at least one surface of a substrate, and sequentially subjecting it to drying and rolling processes to form an active layer, thereby obtaining the electrode sheet. This results in a relatively smooth surface for the electrode sheet. When the surface of the electrode sheet is photographed, the primary particles of the electrode active material in the obtained image are essentially at the same horizontal position within the same field of view, which can further reduce imaging depth-of-field interference and thus further improve the accuracy of the measured particle size distribution of the primary particles of the electrode active material.

[0091] For example, an electrode paste comprising an electrode active material and a binder may be disposed on at least one surface of a substrate, or on two opposing surfaces of a substrate.

[0092] In some embodiments, the surface roughness Ra of the substrate to which the active layer is formed is less than or equal to 3.2 μm. This design results in a relatively smooth surface on the substrate to which the active layer is formed. When photographing the surface of the electrode, the primary particles of the electrode active material in the obtained image are essentially at the same horizontal position in the same field of view, which can further reduce imaging depth-of-field interference and thus further improve the accuracy of the measured particle size distribution of the primary particles of the electrode active material.

[0093] Surface roughness is a common method for characterizing microscopic unevenness. The greater the surface roughness, the higher the surface unevenness; the smaller the surface roughness, the higher the surface smoothness. Non-limitingly, surface roughness can be tested using conventional surface roughness testing methods in the art, including but not limited to: referring to standard GB / T 2523-2022.

[0094] In some embodiments, the electrode active material includes a positive electrode active material or a negative electrode active material.

[0095] In some embodiments, the positive electrode active material includes one or more of lithium-ion secondary battery positive electrode active materials and sodium-ion secondary battery positive electrode active materials.

[0096] In some embodiments, the positive electrode active material of a lithium-ion secondary battery includes one or more of lithium phosphate, ternary cathode materials, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, and lithium nickel manganese oxide. Non-limiting examples of lithium cobalt oxide may include LiCoO2; non-limiting examples of lithium nickel oxide may include LiNiO2; and non-limiting examples of lithium manganese oxide may include LiMnO2, LiMn2O4, etc.

[0097] In some embodiments, the positive electrode active material includes one or more of lithium phosphate and ternary positive electrode materials.

[0098] In some embodiments, the positive electrode active material comprises only lithium phosphate, and the compaction density of the electrode sheet is 2 g / cm³. 3 ~2.6g / cm 3 The compaction density of the electrode sheet is within the above-mentioned range, which can reduce the probability of lithium phosphate particles breaking, thereby further improving the accuracy of the primary particle size distribution of the electrode active material measured by the above-mentioned method. For example, the compaction density of the electrode sheet includes, but is not limited to, 2 g / cm³. 3 2.1g / cm 3 2.2g / cm 3 2.3g / cm 3 2.4g / cm 3 2.5g / cm 3 2.6g / cm3 Or the range between any two of the aforementioned.

[0099] In some embodiments, lithium phosphates include those with the chemical formula Li m A a Fe x D d P y E e O z G g The material comprises, wherein A includes at least one element selected from Al, Na, K and Mg; D includes at least one element selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti and V; E includes at least one element selected from B, S, Si and N; G includes at least one element selected from S, F, Cl and Br; 0.5≤m≤1.5, 0≤a≤0.1, 0.5≤x≤1, 0≤d≤0.5, 0.5≤y≤1, 0≤e≤0.5, 3.5≤z≤4, and 0≤g≤0.5.

[0100] In some embodiments, the positive electrode active material includes only ternary positive electrode material, and the compaction density of the electrode sheet is 3.3 g / cm³. 3 ~3.6g / cm 3 The compaction density of the electrode sheet is within the above-mentioned range, which can reduce the probability of breakage of ternary cathode material particles, thereby further improving the accuracy of the primary particle size distribution of the electrode active material measured by the above-mentioned method. For example, the compaction density of the electrode sheet includes, but is not limited to, 3.3 g / cm³. 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 Or the range between any two of the aforementioned.

[0101] In some embodiments, the ternary cathode material includes one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt manganese oxide, and modified compounds thereof. Non-limiting examples of lithium nickel cobalt manganese oxide may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.8 Co 0.15 Al 0.05 O2.

[0102] In some embodiments, the positive electrode active material of a sodium-ion secondary battery may include one or more of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion secondary batteries may also be used.

[0103] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. A non-limiting example of a sodium transition metal oxide is Na. x1 MO2, where M can include one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x1 ≤ 1.

[0104] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be one or more of P, S, and Si; n represents (YO4). n- The price state.

[0105] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds consisting of anionic units and halide anions. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may be one or more of P, S, and Si, and n represents (YO4). n- The valence state; halogens can be one or more of F, Cl and Br.

[0106] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+And a class of compounds with optional halide anions. Y can be one or more of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents (ZO). y ) m+ The valence state; halogens can be one or more of F, Cl and Br.

[0107] Polyanionic compounds can include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F and Na3(VO y )2(PO4)2F 3-2y1 One or more of (0≤y1≤1). Among them, M' in NaM'PO4F can include one or more of V, Fe, Mn and Ni.

[0108] Prussian blue compounds can contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds containing Prussian blue. Transition metals may include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. A non-limiting example of Prussian blue compounds is Na. a1 Me b1 Me' c1 (CN)6, wherein Me and Me' can each be one or more of Ni, Cu, Fe, Mn, Co and Zn, 0 < a1 ≤ 2, 0 < b1 < 1, 0 < c1 < 1.

[0109] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used.

[0110] In some embodiments, the step of calculating the number and proportion statistics of primary particles in different particle size ranges includes: calculating one or more of the following parameters (1) to (17):

[0111] (1) Statistical value of the number of primary particles larger than 3μm;

[0112] (2) Statistical value of the number of primary particles larger than 1 μm;

[0113] (3) Statistical value of the number of primary particles smaller than 100nm;

[0114] (4) Statistical value of the number of primary particles smaller than 150nm;

[0115] (5) Statistical value of the number of primary particles smaller than 200nm;

[0116] (6) Statistical value of the proportion of primary particles larger than 3μm in primary particles;

[0117] (7) Statistical value of the proportion of primary particles larger than 1 μm in primary particles;

[0118] (8) The statistical value of the proportion of primary particles smaller than 100nm in primary particles;

[0119] (9) Statistical value of the proportion of primary particles smaller than 150nm in primary particles;

[0120] (10) The statistical value of the proportion of primary particles smaller than 200 nm in primary particles;

[0121] (11) Dn1 of primary particles;

[0122] (12) Dn2 of primary particles;

[0123] (13) Dn3 of primary particles;

[0124] (14) Dn10 of primary particles;

[0125] (15) Dn50 of primary particles;

[0126] (16) Dn90 of primary particles;

[0127] (17) Dn99 of primary particles.

[0128] Since the particle size distribution of the primary particles of the electrode active material is related to the compaction density of the electrode sheet, the DCR of the secondary battery, the rate performance and the high-temperature storage, etc., statistical analysis of one or more of the above parameters (1) to (17) is beneficial to adjust the compaction density of the electrode sheet, or to improve the DCR, rate performance and the high-temperature storage of the secondary battery.

[0129] In this application, Dn1, Dn2, Dn3, Dn10, Dn50, Dn90, and Dn99 represent the particle size of primary particles when the cumulative percentage reaches 1%, 2%, 3%, 10%, 50%, 90%, and 99%, respectively. That is, the number of primary particles with particle sizes smaller than 1%, 2%, 3%, 10%, 50%, 90%, and 99% accounts for 1%, 2%, 3%, 10%, 50%, 90%, and 99% of the total number of primary particles, respectively. For example, Dn10 indicates that 10% of the primary particles have a particle size smaller than this value.

[0130] In some embodiments, the adhesive includes one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0131] In some embodiments, the substrate material includes one or more of metals and polymers.

[0132] As a non-limiting example, the metallic material includes one or more of aluminum, aluminum alloys, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys; the polymer includes polyimide, for example, the matrix may be a polyimide sheet.

[0133] In some embodiments, the substrate may be a current collector, which includes a metal foil or a composite current collector. For example, aluminum foil or copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate; non-limiting examples of the metal material may include one or more of aluminum, aluminum alloys, copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys; non-limiting examples of the polymeric material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE) substrates.

[0134] In some embodiments, the electrode sheet can be prepared by dispersing the components used to prepare the electrode sheet, such as electrode active materials, binders, and any other components, in a solvent to form an electrode slurry; coating the electrode slurry onto at least one surface of a current collector, and then performing processes such as drying and cold pressing to obtain the electrode sheet. The solvent can be selected from, but is not limited to, N-methylpyrrolidone (NMP) or deionized water. The current collector surface coated with the electrode slurry can be a single surface of the current collector or both surfaces of the current collector.

[0135] Another embodiment of this application provides a method for preparing a secondary battery, including a step of measuring the primary particle size distribution of an electrode active material, the measuring step including the method for measuring the primary particle size distribution of the electrode active material described above in this application.

[0136] Another embodiment of this application provides a computer device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the steps of the measurement method described above in this application.

[0137] Another embodiment of this application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the measurement method described above.

[0138] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where the technology or conditions are not specified in the embodiments, they are performed according to the technology or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0139] Example 1

[0140] A method for determining the primary particle size distribution of a positive electrode active material includes the following steps:

[0141] (1) Weigh 159g NMP (N-methylpyrrolidone) and add it to the mixing tank. Stir at 800 rpm. Weigh 6g PVDF (polyvinylidene fluoride) and slowly add it to the mixing tank. Gradually increase the speed to 1200 rpm and stir for 1 hour to obtain the adhesive solution.

[0142] (2) Add 5.7g of binder solution and 3.8g of positive electrode active material lithium iron phosphate (LiFePO4) into the mixing box, place the mixing box in the self-rotating and revolution-rotating mixer and start the program to stir. Pre-stir at 800rpm for 1min and automatically stir at 2000rpm for 10min to obtain positive electrode slurry.

[0143] (3) Ethanol was evenly sprayed onto a clean glass plate, and then a current collector Al foil (substrate) was attached to the surface of the glass plate. The above positive electrode slurry was evenly spread on the front end of the current collector. A 150μm doctor blade was placed on the front end of the positive electrode slurry, and the coating machine was started to allow the doctor blade to coat at a uniform speed. The coated electrode was placed in a 100℃ forced-air drying oven and dried for 2 hours. Then, it was cold-pressed. The compacted density of the resulting electrode was 2.1 g / cm³. 3 The active layer formed by the positive electrode slurry is located on one surface of the current collector, and the surface roughness Ra of the current collector with the active layer is 1.6 μm.

[0144] (4) The surface of the active layer of the electrode away from the current collector was photographed using SEM. The SEM was in secondary electron mode with magnifications of 5k and 10k. 20 SEM images were taken at 5k magnification and 30 SEM images were taken at 10k magnification. The SEM model was Thermo Fisher Apreo 2S, and the test parameters were HV 10.0kV, curr 0.40nA, and secondary electron imaging mode (SE). The SEM image at 5k magnification is shown in Figure 2. The scale bar in Figure 2 is 5μm. It can be seen from Figure 2 that the positive electrode active material particles in the electrode are relatively uniformly distributed and the boundaries between the particles are obvious.

[0145] (5) The bounding rectangles of the primary particles of the positive electrode active material in multiple SEM images were obtained by software fitting. The particle size L1 of the primary particles of the positive electrode active material was calculated based on the diagonal length of the bounding rectangles. Where L2 is the length of the diagonal of the circumscribed rectangle, the obtained L1 data is exported;

[0146] Specifically, the bounding rectangles of the primary particles of the positive electrode active material in multiple SEM images were obtained by fitting and processing using Particle processing software. The parameters were set as follows: magnification 0.5 to 2 times, and image segmentation 512 to 9999.

[0147] Select the image area to be processed, and set the image height (H) and width (W) parameters according to the "Actual Length". Mark the horizontal distance between two points at the center of the leftmost and rightmost positions of the ruler, and click "Set as Ruler Length".

[0148] After setting the parameters, click "Start Analysis", select the report save path, open the report data, click download raw data, and obtain L1 data;

[0149] (6) Import the L1 data into an Excel spreadsheet. Based on the particle size of the primary particles of the positive electrode active material, calculate the total number of primary particles of the positive electrode active material across the entire particle size range, the number of primary particles <100nm and their proportion in the primary particles, the number of primary particles <150nm and their proportion in the primary particles, the number of primary particles <200nm and their proportion in the primary particles, the number of primary particles >1μm and their proportion in the primary particles, Dn10, Dn50, and Dn90, and then take the average value. The results are shown in Table 1.

[0150] Example 2

[0151] A method for determining the primary particle size distribution of a positive electrode active material includes the following steps:

[0152] (1) Weigh 159g NMP (N-methylpyrrolidone) and add it to the mixing tank. Stir at 800 rpm. Weigh 6g PVDF (polyvinylidene fluoride) and slowly add it to the mixing tank. Gradually increase the speed to 1200 rpm and stir for 1 hour to obtain the adhesive solution.

[0153] (2) Add 5.7g of binder solution and 3.6g of positive electrode active material lithium manganese iron phosphate (LiFeMnPO4) into the mixing box, place the mixing box in the self-rotating and revolution-rotating mixer and start the program to stir. Pre-stir at 800rpm for 1min and automatically stir at 2000rpm for 10min to obtain positive electrode slurry.

[0154] (3) Ethanol was evenly sprayed onto a clean glass plate, and then a current collector Al foil (substrate) was attached to the surface of the glass plate. The above positive electrode slurry was evenly spread on the front end of the current collector. A 150μm doctor blade was placed on the front end of the positive electrode slurry, and the coating machine was started to allow the doctor blade to coat at a uniform speed. The coated electrode was placed in a 100℃ forced-air drying oven and dried for 2 hours. Then, it was cold-pressed. The compacted density of the resulting electrode was 2.2 g / cm³. 3 The active layer formed by the positive electrode slurry is located on one surface of the current collector, and the surface roughness Ra of the current collector with the active layer is 1.6 μm.

[0155] (4) Use SEM to photograph the surface of the active layer of the electrode away from the current collector. The SEM is in backscatter mode with a magnification of 15k and 20 SEM images are taken at this magnification. The SEM model is Thermo Fisher Apreo 2S, and the test parameters are HV 10.0kV, curr 0.40nA, and backscatter electron imaging mode.

[0156] (5) The bounding rectangles of the primary particles of the positive electrode active material in multiple SEM images were obtained by software fitting. The particle size L1 of the primary particles of the positive electrode active material was calculated based on the diagonal length of the bounding rectangles. Where L2 is the length of the diagonal of the circumscribed rectangle, the obtained L1 data is exported;

[0157] Specifically, the bounding rectangles of the primary particles of the positive electrode active material in multiple SEM images were obtained by fitting and processing using Particle processing software. The parameters were set as follows: magnification 0.5 to 2 times, and image segmentation 512 to 9999.

[0158] Select the image area to be processed, and set the image height (H) and width (W) parameters according to the "Actual Length". Mark the horizontal distance between two points at the center of the leftmost and rightmost positions of the ruler, and click "Set as Ruler Length".

[0159] After setting the parameters, click "Start Analysis", select the report save path, open the report data, click download raw data, and obtain L1 data;

[0160] (6) Import the L1 data into an Excel spreadsheet. Based on the particle size of the primary particles of the positive electrode active material, calculate the total number of primary particles of the positive electrode active material across the entire particle size range, the number of primary particles <100nm and their proportion in the primary particles, the number of primary particles <150nm and their proportion in the primary particles, the number of primary particles <200nm and their proportion in the primary particles, the number of primary particles >1μm and their proportion in the primary particles, Dn10, Dn50, and Dn90, and then take the average value.

[0161] Example 3

[0162] The method for determining the primary particle size distribution of the positive electrode active material is basically the same as in Example 2, except that the primary particle size distribution of lithium manganese iron phosphate used in step (2) is different.

[0163] Compared to Example 2, the lithium manganese iron phosphate used in Example 3 has a smaller proportion of small particles in its primary particles.

[0164] The results of the primary particle size distribution obtained by the determination methods in Examples 2 and 3 are shown in Table 1.

[0165] Comparative Example 1

[0166] The particle size of the same positive electrode active material, lithium iron phosphate (LiFePO4), used in step (2) of Example 1 was tested using a laser particle size analyzer. Specifically, 1-3 drops of 1% dispersant and 20 mL of deionized water were added to the lithium iron phosphate. The dispersant was X3204. The mixture was sonicated for 5 min at 53 kHz / 120 W to form a dispersion. The primary particles of lithium iron phosphate in the dispersion were measured using a MasterSizer 3000 laser particle size analyzer. The range of the laser particle size analyzer was 0.01 μm to 3500 μm. The main light source was a helium-neon red light source, and the auxiliary light source was a blue light source. An inverse Fourier transform optical system was used, and the detection angle was 0.015° to 144°. The Dn10, Dn50, and Dn90 of the primary particles of the positive electrode active material were obtained.

[0167] Comparative Example 2

[0168] The particle size of the same positive electrode active material, lithium iron phosphate (LiFePO4), used in step (2) of Example 1 was directly measured using SEM. The SEM was performed in secondary electron imaging mode with magnifications of 5k and 10k. 20 SEM images were taken at 5k magnification and 30 SEM images were taken at 10k magnification. The SEM model was Thermo Fisher Apreo 2S. The total number of primary particles of the positive electrode active material, the number of primary particles <100nm and their proportion in the primary particles, the number of primary particles <150nm and their proportion in the primary particles, the number of primary particles <200nm and their proportion in the primary particles, the number of primary particles >1μm and their proportion in the primary particles, Dn10, Dn50, and Dn90 were calculated.

[0169] Comparative Example 3

[0170] The particle size of the same positive electrode active material, lithium iron phosphate (LiFeMnPO4), used in step (2) of Example 2 was tested using a laser particle size analyzer. Specifically, 1-3 drops of 1% dispersant and 20 mL of deionized water were added to the lithium iron phosphate. The dispersants were X3204 and 4105. The mixture was sonicated for 5 min at 53 kHz / 120 W to form a dispersion. The primary particles of lithium iron phosphate in the dispersion were measured using a MasterSizer 3000 laser particle size analyzer. The range of the laser particle size analyzer was 0.01 μm to 3500 μm. The main light source was a helium-neon red light source, and the auxiliary light source was a blue light source. An inverse Fourier transform optical system was used, and the detection angle was 0.015° to 144°. The Dn10, Dn50, and Dn90 of the primary particles of the positive electrode active material were obtained.

[0171] Comparative Example 4

[0172] The particle size of the same positive electrode active material, lithium iron manganese phosphate (LiFeMnPO4), used in step (2) of Example 2 was directly measured using SEM. The SEM was taken in backscattered electron imaging mode at a magnification of 15k, and 20 SEM images were taken at this magnification. The SEM model was Thermo Fisher Apreo 2S. The total number of primary particles of the positive electrode active material, the number of primary particles <100nm and their proportion in the primary particles, the number of primary particles <150nm and their proportion in the primary particles, the number of primary particles <200nm and their proportion in the primary particles, the number of primary particles >1μm and their proportion in the primary particles, Dn10, Dn50, and Dn90 were calculated.

[0173] Comparative Example 5

[0174] The particle size of the same positive electrode active material, lithium iron manganese phosphate (LiFeMnPO4), in step (2) of Example 3 was tested using a laser particle size analyzer. Specifically, 1-3 drops of 1% dispersant and 20 mL of deionized water were added to the lithium iron manganese phosphate. The dispersants were X3204 and 4105. The mixture was sonicated for 5 min at 53 kHz / 120 W to form a dispersion. The primary particles of lithium iron manganese phosphate in the dispersion were measured using a MasterSizer 3000 laser particle size analyzer. The range of the laser particle size analyzer was 0.01 μm to 3500 μm. The main light source was a helium-neon red light source, and the auxiliary light source was a blue light source. An inverse Fourier transform optical system was used, and the detection angle was 0.015° to 144°. The positive electrode active materials Dn10, Dn50, and Dn90 were obtained.

[0175] Comparative Example 6

[0176] The particle size of the same positive electrode active material, lithium iron manganese phosphate (LiFeMnPO4), used in step (2) of Example 3 was directly tested using SEM. The SEM was performed in backscattered electron imaging mode with a magnification of 15k, and 20 SEM images were taken at this magnification. The SEM model was Thermo Fisher Apreo 2S. The total number of primary particles of the positive electrode active material, the number of primary particles <100nm and their proportion in the primary particles, the number of primary particles <150nm and their proportion in the primary particles, the number of primary particles <200nm and their proportion in the primary particles, the number of primary particles >1μm and their proportion in the primary particles, Dn10, Dn50, and Dn90 were calculated.

[0177] The test data of the primary particle size of the positive electrode active materials obtained from Comparative Examples 1 to 6 are shown in Table 1.

[0178] Table 1

[0179] In Table 1, SEM images at 5k magnification were used in Example 1 and Comparative Example 2 to count the number of primary particles >1μm and their proportion in the primary particles in the positive electrode active material, and SEM images at 10k magnification were used to count the number of primary particles <100nm and their proportion in the primary particles, the number of primary particles <150nm and their proportion in the primary particles, the number of primary particles <200nm and their proportion in the primary particles, Dn10, Dn50, and Dn90 in the positive electrode active material.

[0180] The number of primary particles >1μm in the positive electrode active material measured in Example 2 and Comparative Example 4 was 0, indicating that the particle size of the primary particles in the positive electrode active material used in Example 2 and Comparative Example 4 was ≤1μm.

[0181] The determination methods of Comparative Examples 1, 3 and 5 can obtain the Dn10, Dn50 and Dn90 of primary particles in the positive electrode active material, but cannot directly obtain the total number of primary particles, the number of primary particles <100nm and their proportion in the primary particles, the number of primary particles <150nm and their proportion in the primary particles, the number of primary particles <200nm and their proportion in the primary particles, and the number of primary particles >1μm and their proportion in the primary particles.

[0182] The data in Table 1 shows the following:

[0183] Comparing Example 1 with Comparative Examples 1-2, Example 2 with Comparative Examples 3-4, and Example 3 with Comparative Examples 5-6, it can be found that when counting primary particles within the same particle size range at the same magnification, Examples 1-3 collected more primary particles than Comparative Examples 2, 4, and 6. In Comparative Examples 2, 4, and 6, the uneven dispersion of primary particles resulted in significant differences in image contrast, making it difficult to identify small particles. Compared to Examples 1-3, Comparative Examples 1, 3, and 5 showed larger Dn10, Dn50, and Dn90 values ​​for the primary particles. This is because the primary particles in Comparative Examples 1, 3, and 5 agglomerated, making it impossible to identify more small particles. This indicates that the measurement method in Examples 1-3 yielded a smaller error and higher accuracy in determining the particle size of the primary particles in the positive electrode active material.

[0184] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0185] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for determining the primary particle size distribution of an electrode active material, comprising the following steps: Multiple images are obtained by photographing the cross-section or surface of the active layer of the electrode; the active layer contains the electrode active material; The particle size of the primary particles of the electrode active material in multiple images was measured. Based on the particle size of the primary particles of the electrode active material, calculate the statistical value of the number of primary particles across the entire particle size range; The number and proportion of primary particles in different particle size ranges are calculated to obtain the particle size distribution of the primary particles in the electrode active material.

2. The determination method according to claim 1, wherein, The active layer does not contain a conductive agent.

3. The determination method according to claim 1 or 2, wherein, The steps of photographing the cross-section or surface of the active layer of the electrode include: Use SEM to photograph the cross-section or surface of the active layer of the electrode.

4. The determination method according to any one of claims 1 to 3, wherein, The step of measuring the particle size of the primary particles of the electrode active material in multiple images includes: Obtain the circumscribed rectangle of the primary particles of the electrode active material in the image. Calculate the particle size L1 of the primary particles of the electrode active material based on the diagonal length of the circumscribed rectangle. L1 satisfies the following: Where L2 is the length of the diagonal of the circumscribed rectangle.

5. The determination method according to any one of claims 1 to 4, wherein, The number of images at the same magnification is 10 to 50.

6. The determination method according to any one of claims 1 to 5, wherein, The method for preparing the electrode sheet includes the following steps: depositing an electrode slurry containing the electrode active material and a binder on at least one surface of a substrate, and sequentially subjecting it to drying and rolling processes to form the active layer, thereby obtaining the electrode sheet.

7. The determination method according to claim 6, wherein, The electrode active material includes positive electrode active material or negative electrode active material.

8. The determination method according to claim 7, wherein, The positive electrode active material includes one or more of lithium phosphate and ternary positive electrode materials.

9. The determination method according to any one of claims 7 to 8, wherein, The positive electrode active material consists only of lithium phosphate, and the compaction density of the electrode sheet is 2 g / cm³. 3 ~2.6g / cm 3 .

10. The determination method according to any one of claims 8 to 9, wherein, The lithium-containing phosphate includes those with the chemical formula Li m A a Fe x D d P y E e O z G g The material comprises, wherein A includes at least one element selected from Al, Na, K and Mg; D includes at least one element selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, Ti and V; E includes at least one element selected from B, S, Si and N; G includes at least one element selected from S, F, Cl and Br; 0.5≤m≤1.5, 0≤a≤0.1, 0.5≤x≤1, 0≤d≤0.5, 0.5≤y≤1, 0≤e≤0.5, 3.5≤z≤4, and 0≤g≤0.

5.

11. The determination method according to any one of claims 7 to 8, wherein, The positive electrode active material includes only ternary positive electrode material, and the compaction density of the electrode sheet is 3.3 g / cm³. 3 ~3.6g / cm 3 .

12. The determination method according to any one of claims 1 to 11, wherein, The steps for calculating the number and percentage statistics of primary particles in different particle size ranges include: calculating one or more of the following parameters (1) to (17): (1) Statistical value of the number of primary particles larger than 3μm; (2) Statistical value of the number of primary particles larger than 1 μm; (3) Statistical value of the number of primary particles smaller than 100nm; (4) Statistical value of the number of primary particles smaller than 150nm; (5) Statistical value of the number of primary particles smaller than 200nm; (6) The statistical value of the proportion of primary particles larger than 3 μm in the total number of primary particles; (7) The statistical value of the proportion of primary particles larger than 1 μm in the total number of primary particles; (8) The statistical value of the proportion of primary particles smaller than 100 nm in the primary particles; (9) The statistical value of the proportion of primary particles smaller than 150 nm in the primary particles; (10) The statistical value of the proportion of primary particles smaller than 200 nm in the primary particles; (11) Dn1 of the primary particles; (12) Dn2 of the primary particles; (13) Dn3 of the primary particles; (14) The Dn10 of the primary particles; (15) Dn50 of the primary particles; (16) The Dn90 of the primary particles; (17) The Dn99 of the primary particles.

13. The determination method according to any one of claims 6 to 11, wherein, The adhesive includes one or more of the following: polyvinylidene fluoride, sodium carboxymethyl cellulose, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

14. The determination method according to any one of claims 6 to 11, wherein, The substrate material includes one or more of metals and polymers.

15. A method for preparing a secondary battery, comprising a step of measuring the primary particle size distribution of an electrode active material, wherein the measuring step comprises the method for measuring the primary particle size distribution of the electrode active material according to any one of claims 1 to 14.

16. A computer device comprising a memory and a processor, the memory storing a computer program, the processor executing the computer program to implement the steps of the measurement method according to any one of claims 1 to 14.

17. A computer-readable storage medium having a computer program stored thereon, the computer program being executed by a processor to implement the steps of the measurement method according to any one of claims 1 to 14.

Images