Method for measuring opening degree, positive electrode active material, positive electrode plate, and electrochemical device

Abstract

The invention provides an opening degree determination method, a positive electrode active material, a positive electrode plate and an electrochemical device. The method for measuring the opening degree comprises the following steps: measuring the total specific surface area BET, the apparent density rho and the equivalent sphere surface area average particle size D of the positive electrode active material; measuring the external specific surface area ESS of the positive electrode active material; and calculating an opening degree OPA of the positive electrode active material based on the ESS; eSS meets the formula I: ESS = 6 / (ACS * rho * D); the OPA meets the formula II: OPA = (BET-ESS) / BET * 100%; wherein BET represents the total specific surface area of the positive electrode active material; aCS represents the average comprehensive sphericity index of the positive electrode active material. According to the method, the quantitative relation between the opening degree and the sphericity degree is established, and a standard is provided for material evaluation. And the prepared material can synchronously optimize pores and morphology structures, so that the battery can maintain cycle stability and safety while the capacity is improved.

Description

Technical Field

[0001] This application relates to the field of battery material preparation technology, and in particular to methods for measuring porosity, positive electrode active materials, positive electrode sheets, and electrochemical devices. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the market has placed higher demands on the energy density, cycle life, and safety and reliability of lithium-ion batteries. As the core component determining battery performance, the microstructure design and precise characterization of cathode active materials have become crucial for driving battery technology upgrades. Currently, the industry lacks systematic quantitative guidance at the structural design level when improving cathode material performance. Research shows that the porous structure of the material surface can effectively improve ion transport efficiency and capacity utilization, but excessively high porosity can exacerbate side reactions and affect structural stability. Meanwhile, the morphology of particles has a significant impact on the processing performance and long-term cycling stability of electrodes. However, existing testing methods for characterizing this key feature of particle morphology have obvious limitations in terms of accuracy and statistical reliability. Specifically, the currently widely used morphology analysis method based on microscopic images is susceptible to the influence of sample preparation, image acquisition quality, and subsequent image processing algorithm parameters. Furthermore, due to the limited number of samples analyzed, it is difficult to guarantee the statistical representativeness of the overall morphology characteristics of batch materials. This measurement uncertainty directly leads to a lack of unified, stable, and repeatable standards for the quantitative description of key morphological parameters of materials. Due to the shortcomings of the aforementioned characterization techniques, existing technologies have not yet established a systematic scheme that can simultaneously optimize porous structure and particle morphology and clarify their reasonable range. Material development still relies on empirical trials, making it difficult to achieve the optimal balance between capacity, lifetime, and processability. Summary of the Invention

[0003] In view of this, in order to solve at least one of the above problems, this application proposes a method for measuring the porosity of positive electrode active materials, aiming to establish a unified and highly accurate quantitative characterization standard for the key microstructure of positive electrode active materials, and to provide a more reliable quantitative basis for material research and development and performance optimization.

[0004] In addition, this application also provides materials and electrochemical devices.

[0005] In a first aspect, this application provides a method for determining the porosity of a positive electrode active material. The method includes: determining the total specific surface area (BET), apparent density (ρ), and average particle size (D) of the equivalent spherical surface area of ​​the positive electrode active material; determining the external specific surface area (ESS) of the positive electrode active material; and calculating the porosity (OPA) of the positive electrode active material based on the ESS; wherein the ESS satisfies Formula 1: ESS = 6 / (ACS × ρ × D); and the OPA satisfies Formula 2: OPA = (BET - ESS) / BET × 100%; wherein BET represents the total specific surface area of ​​the positive electrode active material; and ACS represents the average comprehensive sphericity index of the positive electrode active material.

[0006] Based on the first aspect, in some embodiments of this application, the ACS testing method includes: acquiring scanning electron microscope images and laser particle size distribution data of the positive electrode active material; determining the particle size distribution radius Span of the positive electrode active material based on the laser particle size distribution data; and acquiring the projected area S of the nth particle based on the scanning electron microscope image. n Perimeter P n minor axis length D n and major axis length L n ; Determine the comprehensive sphericity index CS of the nth particle. n ; and based on the CS n The ACS is measured; wherein the CS n Satisfying Formula 3: CS n =α×YS n +β×K; the YS n Satisfying Formula 4: YS n =(Y n ×R n ) 0.5 The Y n Satisfying Formula 5: Y n =4π×S n / (P) n ) 2 The R n Satisfying Formula Six: R n =D n / L n The K satisfies Formula 7: K = a × e （-b×Span） +c; The Span satisfies Formula 8: Span = (D90 - D10) / D50; The ACS satisfies Formula 9: ACS = (CS1 + CS2 + CS) n ) / n; where, the YS n The normalized image sphericity parameter for each particle; K is the sphericity compensation factor for the particle; Y... nThe R represents the roundness of the nth particle; n The aspect ratio of the nth particle is represented; D10, D50, and D90 are characteristic particle sizes obtained from the laser particle size distribution curve; wherein, D10 represents the particle size corresponding to a cumulative volume distribution of 10%, D50 represents the particle size corresponding to a cumulative volume distribution of 50%, and D90 represents the particle size corresponding to a cumulative volume distribution of 90%; n represents the number of particles counted; CS1, CS2, and CS... n These are the comprehensive sphericity indices for the 1st, 2nd to nth particles, respectively; e is a natural constant; α and β represent weighting coefficients and satisfy α+β=1; a, b, and c represent model coefficients; α, β, a, b, and c are all determined by calibration using standard samples with known sphericity.

[0007] Secondly, this application provides a positive electrode active material, the positive electrode active material comprising core-shell structured particles, the particles comprising a core and a coating layer covering the core; the coating layer having openings; the porosity of the openings is represented by OPA, and the average comprehensive sphericity index of the particles is represented by ACS; the OPA and the ACS satisfy: 40%≤OPA≤66%; 0.85≤ACS≤0.98; wherein, the OPA and the ACS are measured using the aforementioned method for measuring the porosity and average comprehensive sphericity index of positive electrode active materials.

[0008] Based on the second aspect, in some embodiments of this application, 50%≤OPA≤66%; 0.90≤ACS≤0.98.

[0009] Based on the second aspect, in some embodiments of this application, the D50 satisfies: 2.0µm≤D50≤6.0µm.

[0010] Based on the second aspect, in some embodiments of this application, the BET satisfies: 0.3m² / g ≤ BET ≤ 1.5m² / g.

[0011] Based on the second aspect, in some embodiments of this application, the general chemical formula of the positive electrode active material is Li. x Ni y M z O2, wherein M contains at least two elements selected from Co, Mn, Al, Sr, Ti, W, P, Mo, Sn, B, Sb, Nb, Zr, and satisfies 0.9≤x≤1.2, 0≤y≤1, and 0≤z≤1.

[0012] Based on the second aspect, in some embodiments of this application, the positive electrode active material includes closed pores; the closed pores are enclosed pores located inside the core, and the enclosed pores are not in communication with the outer surface of the particles; the porosity of the closed pores is P. 闭 The P 闭 ≤3%; the P 闭 Satisfying Formula 10: P 闭 =(1 / p 真 -1 / p 实 ) / V 表 ×100%; Wherein, the V 表 The p represents the apparent volume of the positive electrode active material per unit mass; 真 p represents the true density of the positive electrode active material. 实 p represents the density of the positive electrode active material in the absence of any pores. 实 It can be obtained directly from XRD analysis.

[0013] Thirdly, this application provides a positive electrode sheet, including a current collector and a positive electrode material layer located on the current collector, wherein the positive electrode material layer comprises the aforementioned positive electrode active material.

[0014] Fourthly, this application provides an electrochemical device comprising a positive electrode, the positive electrode comprising a current collector and a positive electrode material layer located on the current collector, the positive electrode material layer comprising the aforementioned positive electrode active material.

[0015] Compared to existing technologies, the porosity determination method for positive electrode active materials provided in this application aims to specifically characterize two key structural parameters affecting the performance of positive electrode materials: one is the "average comprehensive sphericity index," which is closely related to the material's fluidity, electrode processing uniformity, and electrode structure stability; the other is "porosity," which directly affects the material's lithium-ion transport efficiency, electrolyte wettability, and available electrochemical active area, thereby determining the battery's capacity utilization and rate performance. This application establishes clear mathematical relationships and standardized measurement procedures between these two parameters, as well as between them and other physical properties such as total specific surface area and apparent density. This solves problems in existing technologies such as incomparable data due to unclear parameter definitions and inconsistent measurement methods, difficulties in studying structure-property relationships, and a lack of precise guidance for process optimization. The "average comprehensive sphericity index" and "porosity" measured by this method can provide direct quantitative evidence for evaluating and predicting the material's processing performance (such as compaction density and electrode adhesion) and electrochemical performance (such as initial efficiency, cycle capacity retention, and high-rate discharge capability). Attached Figure Description

[0016] Figure 1This is a process flow diagram of the method for determining the porosity of the positive electrode active material in this application.

[0017] Figure 2 This is a planar diagram showing the internal structure of the positive electrode active material particles prepared in Example 1 of this application.

[0018] Figure 3 This is a plan view showing the appearance of the positive electrode active material particles prepared in Example 11 of this application.

[0019] Figure 4 This is a plan view showing the appearance and morphology of the positive electrode active material particles prepared in Comparative Example 6 of this application. Detailed Implementation

[0020] The technical solutions of this application are described clearly and in detail below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0021] See Figure 1 In a first aspect, this application provides a method for determining the porosity of a positive electrode active material. The method includes: determining the total specific surface area (BET), apparent density (ρ), and average particle size (D) of the equivalent spherical surface area of ​​the positive electrode active material; determining the external specific surface area (ESS) of the positive electrode active material; and calculating the porosity (OPA) of the positive electrode active material based on ESS; ESS satisfies Formula 1: ESS = 6 / (ACS × ρ × D); OPA satisfies Formula 2: OPA = (BET - ESS) / BET × 100%; where BET represents the total specific surface area of ​​the positive electrode active material; and ACS represents the average comprehensive sphericity index of the positive electrode active material.

[0022] The inventors discovered that existing technologies typically employ general pore characterization methods such as mercury intrusion porosimetry and gas adsorption to assess the pore structure of materials. However, these methods suffer from limitations, including the inability to accurately distinguish and quantify the surface pore structure of particles crucial to lithium-ion battery performance, potential involvement of hazardous substances, and blind spots in specific pore size testing. Therefore, to address the shortcomings of existing methods in specifically, accurately, and safely characterizing the pore structure of critical surfaces in cathode materials, the inventors discovered and established a clear mathematical relationship between open porosity (OPA) and directly measurable physical parameters such as average composite sphericity index (ACS), total specific surface area (BET), apparent density (ρ), and equivalent particle size (D). This application, by employing the aforementioned technical solution, enables the calculation of accurate OPA reflecting the contribution of surface pores through standardized procedures based on conventional and safe physicochemical testing. This provides a highly targeted, repeatable, and proprietary characterization method for materials development that avoids specific safety risks.

[0023] In some embodiments, the ACS testing method includes: acquiring scanning electron microscope images and laser particle size distribution data of the positive electrode active material; determining the particle size distribution radius Span of the positive electrode active material based on the laser particle size distribution data; and obtaining the projected area S of the nth particle based on the scanning electron microscope image. n Perimeter P n minor axis length D n and major axis length L n ; Determine the overall sphericity index CS of the nth particle. n ; and based on CS n Measure ACS.

[0024] CS n Satisfying Formula 3: CS n =α×YS n +β×K.

[0025] YS n Satisfying Formula 4: YS n =(Y n ×R n ) 0.5 .

[0026] Y n Satisfying Formula 5: Y n =4π×S n / (P) n ) 2 .

[0027] R n Satisfying Formula Six: R n =D n / L n .

[0028] K satisfies Formula 7: K = a × e （-b×Span） +c.

[0029] Span satisfies Formula 8: Span = (D90 - D10) / D50.

[0030] ACS satisfies Formula Nine: ACS = (CS1 + CS2 + CS) n ) / n.

[0031] Among them, YS n Y is the sphericity parameter of the normalized image for each particle; K is the sphericity compensation factor for the particle; n R represents the roundness of the nth particle; n The aspect ratio of the nth particle is represented; D10, D50, and D90 are characteristic particle sizes obtained from the laser particle size distribution curve; where D10 represents the particle size corresponding to a cumulative volume distribution of 10%, D50 represents the particle size corresponding to a cumulative volume distribution of 50%, and D90 represents the particle size corresponding to a cumulative volume distribution of 90%; n represents the number of particles counted; CS1, CS2, CS... n These are the comprehensive sphericity indices for the 1st, 2nd to nth particles, respectively; e is the natural constant, approximately equal to 2.71828; α and β represent weighting coefficients, satisfying α+β=1; a, b, and c represent model coefficients; α, β, a, b, and c are all determined by calibration using standard samples with known sphericity.

[0032] It should be noted that particle sphericity is one of the key indicators for evaluating the performance of powder materials, directly affecting their flowability, bulk density, chemical reactivity, and performance in manufacturing processes. Currently, the main method is image analysis, which involves acquiring particle images through SEM or optical microscopy, and then using image processing techniques to extract contour parameters (such as perimeter and area) to calculate sphericity parameters (such as roundness and aspect ratio). The advantage of this method is that it is intuitive and can directly reflect the morphology of the particles. However, it has significant disadvantages, such as limited statistical representativeness (analyzing a few hundred particles is difficult to represent an entire sample of hundreds of millions), results being greatly affected by sample preparation, image quality, and binarization algorithms, and the difficulty in segmenting adhered or overlapping particles, which introduces errors.

[0033] This application introduces laser particle size distribution data as a supplement to macroscopic statistical information and fuses it with microscopic morphology analysis from scanning electron microscopy to establish a comprehensive calculation model that includes compensation factors and weighting coefficients. This approach not only retains the ability of image methods to capture the details of individual particle morphology but also effectively corrects for biases caused by limited sample statistics through the calculation of overall parameters such as particle size distribution and diameter. Furthermore, it reduces the subjective dependence of the analysis results on the quality of a single image and the segmentation algorithm. Therefore, the Average Composite Sphericity Index (ACS) determination method provided in this application enables a more stable, representative, and repeatable quantitative characterization of material sphericity, thus providing a more reliable and standardized evaluation tool for key morphological parameters of cathode materials, supporting precise material development and process control.

[0034] Secondly, this application provides a positive electrode active material comprising core-shell structured particles, each particle including a core and a coating layer covering the core; the coating layer has openings; the porosity of the openings is represented by OPA, and the average comprehensive sphericity index of the particles is represented by ACS; OPA and ACS satisfy the following: 40% ≤ OPA ≤ 66%, 0.85 ≤ ACS ≤ 0.98. OPA and ACS are measured using the method for determining the porosity and average comprehensive sphericity index of the positive electrode active material provided in the first aspect.

[0035] As an example, OPA can be any value or a range of any two values ​​from 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, and 65%. As an example, ACS can be any value or a range of any two values ​​from 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, and 0.98.

[0036] This application, through its standardized measurement method, enables accurate and repeatable quantitative evaluation of key structural parameters of cathode active materials: open porosity (OPA) and average composite sphericity index (ACS), thus providing reliable data for the research and development screening and precise control of production processes for cathode active materials. Furthermore, by synergistically controlling the OPA and ACS of the cathode active material within the aforementioned specific ranges, this application ensures that the cathode active material possesses excellent lithium-ion transport efficiency and a high number of reactive sites to improve battery capacity, while its particle morphology also exhibits good flowability, filling properties, and mechanical strength. This allows electrode sheets made from this material to simultaneously meet the requirements of high energy density and high structural stability, providing a crucial material foundation for the final battery product to achieve a comprehensive performance of high capacity, excellent cycle life, and reliable safety.

[0037] Furthermore, in some embodiments, 0.92 ≤ ACS ≤ 0.98.

[0038] When the average comprehensive sphericity index (ACS) of the positive electrode active material is within the above-mentioned range, it ensures that the material has good flowability and filling properties, which is conducive to achieving high uniformity and high compaction density of the electrode sheets, thereby ensuring that the battery has a high volumetric energy density. At the same time, high sphericity endows the particles with stronger mechanical stability, which helps them maintain structural integrity during battery cycling. In addition, this high sphericity and open porosity (OPA) work together to further ensure the stable and efficient transport of lithium ions within the active material on the basis of achieving high volumetric energy density, reducing the failure of active materials caused by local structural stress concentration or particle breakage, thus providing a solid and durable structural support for the battery to perform and maintain its high capacity performance.

[0039] Based on the second aspect, in some embodiments, 50% ≤ OPA ≤ 66%; 0.90 ≤ ACS ≤ 0.98.

[0040] Based on the second aspect, in some embodiments, D50 satisfies: 2.0µm≤D50≤6.0µm.

[0041] Furthermore, in some embodiments, 5.0 μm ≤ D50 < 6.0 μm.

[0042] As an example, D50 can be any value from 2.0μm, 2.5μm, 3.0μm, 3.5μm, 4.0μm, 4.5μm, 5.0μm, 5.5μm, 5.8μm, and 6.0μm, or a range of any two values ​​therein. The median particle size D50 in this application is within the aforementioned suitable range, which can effectively balance the material's processing performance while ensuring high ionic conductivity to facilitate capacity utilization, avoiding agglomeration and increased processing difficulty caused by excessively small particles. Therefore, the median particle size of the material needs to be within a certain range.

[0043] Based on the second aspect, in some embodiments, BET satisfies: 0.3m² / g ≤ BET ≤ 1.5m² / g.

[0044] As an example, the value of BET can be any one of 0.3m² / g, 0.4m² / g, 0.5m² / g, 0.6m² / g, 0.7m² / g, 0.8m² / g, 0.9m² / g, 1.0m² / g, 1.1m² / g, 1.2m² / g, 1.3m² / g, 1.4m² / g, 1.5m² / g, or a range consisting of any two of these values.

[0045] The total specific surface area (BET) in this application, within the aforementioned suitable range, ensures a good balance between capacity performance and structural stability. This is because a moderate specific surface area provides sufficient lithium-ion transport interfaces to enhance capacity, while avoiding structural degradation due to excessively large specific surface areas or capacity limitations due to excessively small specific surface areas.

[0046] Based on the second aspect, in some embodiments, the general chemical formula of the positive electrode active material is Li. x Ni y M z O2, wherein M contains at least two elements selected from Co, Mn, Al, Sr, Ti, W, P, Mo, Sn, B, Sb, Nb, Zr, and satisfies 0.9≤x≤1.2, 0≤y≤1, and 0≤z≤1.

[0047] As an example, the value of x can be any of the following: 0.90, 0.92, 0.94, 0.96, 0.98, 1.00, 1.02, 1.03, 1.04, 1.06, 1.08, 1.10, 1.03, 1.05, 1.07, 1.12, 1.14, 1.16, 1.18, 1.20, or a range consisting of any two of these values.

[0048] As an example, the value of y can be any of the following values: 0, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, or a range consisting of any two of these values.

[0049] As an example, the value of z can be any of the following values: 0, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, or a range consisting of any two of these values.

[0050] Furthermore, in some embodiments, 0.90 ≤ x ≤ 1.10.

[0051] Furthermore, in some embodiments, 1.03 ≤ x ≤ 1.07.

[0052] Furthermore, in some embodiments, 0.50 ≤ y ≤ 1.0.

[0053] Furthermore, in some embodiments, 0.80 ≤ y ≤ 1.0.

[0054] Furthermore, in some embodiments, 0.90 ≤ y ≤ 1.00.

[0055] Furthermore, in some embodiments, at least two of Co, Mn, Sr, Al, and B are used. Based on the second aspect, in some embodiments, the positive electrode active material includes closed pores; the closed pores are enclosed pores located inside the core, and the enclosed pores are not in communication with the outer surface of the particles; the porosity of the closed pores is P. 闭 P 闭 ≤3%; P 闭 Satisfying Formula 10: P 闭 =(1 / p 真 -1 / p 实 ) / V 表 ×100%; where V 表 p represents the apparent volume of a unit mass of positive electrode active material. 真 p represents the true density of the positive electrode active material. 实 This represents the density of the positive electrode active material in the absence of any pores. 实 It can be obtained directly from XRD analysis.

[0056] As an example, the value of Pclose can be any of the following values: 3%, 2%, 1%, 0.5%, 0.1%, 0.01%, or a range consisting of any two of these values.

[0057] In some embodiments, the average comprehensive sphericity index of the positive electrode active material is controlled by the precursor morphology and sintering process, and the porosity of the positive electrode active material is controlled by surface coating and coating temperature.

[0058] In some embodiments, the positive electrode active material can be applied to the positive electrode material of an all-solid-state battery.

[0059] Thirdly, this application provides a method for preparing the aforementioned positive electrode active material, comprising the following steps: Step 1: Dissolve salts containing nickel, cobalt, and manganese in deionized water in a certain proportion to prepare a mixed metal salt solution.

[0060] Step 2: NaOH aqueous solution as a precipitant and ammonia as a complexing agent are simultaneously added to the mixed metal salt solution to carry out a co-precipitation reaction for 50 to 100 hours. During the reaction, the ammonia concentration, stirring rate and reaction temperature are adjusted to obtain cathode material precursors with different porosity characteristics.

[0061] Step 3: Mix the cathode material precursor, lithium hydroxide and doping additives to obtain the first mixture; place the first mixture in an air atmosphere or an oxygen atmosphere with an oxygen concentration of 50% to 100% for the first sintering to obtain the intermediate product.

[0062] Step 4: Mix the intermediate product, lithium source and coating additive to obtain a second mixture; place the second mixture in an air atmosphere or an oxygen atmosphere with an oxygen concentration of 50% to 100% for a second sintering to obtain the cathode material.

[0063] As an example, the coprecipitation reaction time in step two can be any value of 50h, 55h, 60h, 65h, 70h, 75h, 80h, 85h, 90h, 95h, or 100h, or a range consisting of any two of these values.

[0064] In some embodiments, in step S3, the molar ratio x / y of the cathode material precursor to lithium hydroxide is from 1.01 to 1.09, where x is the molar content of lithium hydroxide and y is the total molar amount of nickel (Ni), cobalt (Co), and manganese (Mn) in the precursor. As an example, the value of x / y can be any one of 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, or 1.09, or a range consisting of any two of these values.

[0065] In some embodiments, in step S3, the doping additive is selected from at least one of Al2O3, MgO, B2O3, ZrO2, SnO2, Nb2O5, TiO2, V2O3, WO3, Sb2O3, and MoO3.

[0066] In some embodiments, the mixing time in step S3 is from 0.2h to 3.0h. As an example, the mixing time can be any value of 0.2h, 0.5h, 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, or a range consisting of any two of these values.

[0067] In some embodiments, in step S3, the sintering temperature for the first sintering is 695°C to 820°C, and the sintering time is 5h to 20h.

[0068] As an example, the first sintering temperature can be any value of 695℃, 700℃, 750℃, 800℃, 830℃ or a range consisting of any two of these values; as an example, the first sintering time can be any value of 5h, 8h, 10h, 12h, 15h, 18h, 20h or a range consisting of any two of these values.

[0069] In some embodiments, in step S4, the sintering temperature of the second sintering is 250°C to 650°C, and the sintering time is 5h to 12h.

[0070] As an example, the second sintering temperature can be any value of 250℃, 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, or 650℃, or a range consisting of any two of these values; the second sintering time can be any value of 5h, 6h, 7h, 8h, 9h, 10h, 11h, or 12h, or a range consisting of any two of these values.

[0071] In some embodiments, the first sintering can be carried out in an atmosphere sintering furnace, wherein the first sintering atmosphere is an oxygen atmosphere with an oxygen concentration of 50% to 100%.

[0072] As an example, in the first sintering, the oxygen concentration can be any value of 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or a range consisting of any two of these values.

[0073] The second sintering can be carried out in an atmosphere sintering furnace, with the sintering atmosphere being an oxygen atmosphere and the oxygen concentration being 50% to 100%.

[0074] As an example, in the second sintering, the oxygen concentration can be any value from 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or a range consisting of any two of these values. Fourthly, this application provides a positive electrode sheet, including a current collector and a positive electrode material layer located on the current collector, the positive electrode material layer comprising the aforementioned positive electrode active material.

[0075] Fifthly, this application provides an electrochemical device comprising a positive electrode, the positive electrode comprising a current collector and a positive electrode material layer located on the current collector, the positive electrode material layer comprising the aforementioned positive electrode active material.

[0076] The following describes some embodiments of this application in detail. Unless otherwise specified, the embodiments and features described below can be combined with each other.

[0077] The present application will be further described below with reference to specific embodiments and comparative examples.

[0078] Test Method 1: In some embodiments of this application, the quality of capacity performance can be derived from the discharge capacity of the secondary battery. In specific implementations, multiple current discharge capacity ranges can be set, and the quality of the secondary battery's capacity performance can be determined based on the discharge capacity of each current.

[0079] This test method proposes a positive electrode active material for lithium-ion batteries, wherein the specific operation of the average comprehensive sphericity index and porosity analysis is as follows.

[0080] Step 1: Scanning electron microscopy (SEM) image acquisition and laser particle size distribution (DPD) testing are performed on the sample. Using a laser particle size analyzer (e.g., Malvern Mastersizer 3000), the volumetric particle size distribution is measured according to standard operating procedures, and D10, D50, D90, and the distribution curve are recorded. Ten fields of view are randomly selected under SEM for image capture, ensuring a moderate number and good dispersion of particles in each field of view, resulting in multiple statistically significant SEM images and a complete particle size distribution curve. ImagePro Plus is used to process the 10 acquired SEM images, performing grayscale conversion, filtering and denoising, and adaptive threshold binarization. Finally, the watershed algorithm is used to separate adhered particles and identify the contours of individual particles.

[0081] Step 2: For each identified particle, calculate its area, perimeter, and major and minor axes based on the smallest circumcircle or equivalent ellipse; Image sphericity parameter calculation: Based on the extracted morphology parameters, calculate one or more image sphericity parameters for each particle, according to the mathematical formula Y=4π×S / P. 2The roundness is calculated, where Y represents the roundness of the bead, S represents the area of ​​the bead's projection, and P represents the perimeter of the bead's projection.

[0082] Step 3: Calculate the aspect ratio using the formula R = D / L, where R represents the particle's aspect ratio, D represents the particle's minor axis length, and L represents the particle's major axis length. The sphericity parameter of the normalized image can be obtained using the formula YS = (Y × R). 0.5 The result is obtained where YS represents the sphericity parameter of the image after particle normalization, Y represents the roundness of the particle, and R represents the aspect ratio of the particle. The particle size data sphericity compensation factor is calculated based on the laser particle size distribution data obtained in the data acquisition step. Characteristic parameters of the particle size distribution are calculated, and a particle size data sphericity compensation factor is calculated based on these characteristic parameters, according to the mathematical formula K=a×e. (-b×Span) +c yields the shape compensation factor (e approximately equal to 2.71828), where K is the sphericity compensation factor for particle size data, and Span is the radius of the laser particle size distribution, obtained by the formula Span = (D90 - D10) / D50, where D10, D50, and D90 are characteristic parameters extracted from the laser particle size distribution curve, and a, b, and c are model coefficients obtained by calibration using standard spherical particle samples.

[0083] Step 4: Calculate the comprehensive sphericity index. Combine the sphericity parameters of each particle's image and the sphericity compensation factor from the particle size data obtained above. Calculate the comprehensive sphericity index for each particle using a weighted average or an established regression model. Then, use the mathematical formula CS... n =α×YS n The overall sphericity index of the particles is obtained by adding β×K, where CS n YS is the comprehensive sphericity index of the nth particle. n The image sphericity parameter represents the normalized image of the nth particle, K is the sphericity compensation factor for particle size data, α and β are weighting coefficients, and α+β=1. The specific values ​​are determined by fitting a standard sample with known sphericity.

[0084] Step 5: Average Composite Sphericity Index Analysis, based on the mathematical formula ACS = (CS1 + CS2 + CS...) n ) / n; to obtain the average comprehensive sphericity index of the material.

[0085] Where BET is the specific surface area of ​​the material tested by the physical adsorption analyzer, and ρ 表 The apparent density of powder materials can be obtained by analysis and testing with an apparent density meter; D 表 The average particle size, representing the surface area of ​​the equivalent sphere of the powder material, can be obtained by laser particle size analysis.

[0086] Example 1 This embodiment provides a ternary cathode material, specifically including the following steps: Step 1: Weigh nickel sulfate, cobalt sulfate, and manganese sulfate according to a nickel-cobalt-manganese molar ratio of 7:1:2. Dissolve nickel sulfate, cobalt sulfate, and manganese sulfate separately in deionized water. Stir and mix the metal solutions to obtain a mixed metal solution with a nickel sulfate concentration of 1.4 mol / L, a cobalt sulfate concentration of 0.2 mol / L, and a manganese sulfate concentration of 0.4 mol / L. Prepare 6 mol / L NaOH as a precipitant and ammonia water as a complexing agent. Add the metal solution, precipitant, and complexing agent simultaneously and continuously to the reactor for co-precipitation reaction. The ammonia concentration is 9.2 g / L, the pH is 12.0, and the water temperature is controlled at 52℃. After the reaction is complete, the precursor of the cathode material is obtained.

[0087] Step 2: Add the cathode material precursor, lithium hydroxide, Al2O3, and ZrO2 to a high-speed mixer at a molar ratio of 1.0:1.05:0.001:0.0015 and mix for 50 minutes at a stirring speed of 110 rpm to obtain a primary mixture. Place the primary mixture into a box-type sintering material for the first sintering. The primary mixture is sintered in an oxygen atmosphere at a temperature of 820°C for 8 hours to obtain the first sintered product.

[0088] Step 3: The first sintering product and H3BO3 are added to a high-speed mixer at a molar ratio of 1.0:0.001 and mixed for half an hour to obtain a secondary mixture. The secondary mixture is then placed in a box-type sintering material for a second sintering. The second mixture is then sintered in an oxygen atmosphere at a temperature of 300℃ for 6 hours to obtain the ternary cathode material.

[0089] Examples 2 to 6: The difference between Examples 2 to 6 and Example 1 is that, except for the ammonia concentration and pH value of the system in step 1, all other conditions remain the same. See Table 1 for the differences.

[0090] Unless otherwise specified, the testing and analysis methods in this application are based on national standards.

[0091] Testing and Inspection: Sulfide all-solid-state mold batteries were fabricated using the cathode materials obtained in Examples 1 to 6, and their capacity performance was tested. The specific details are as follows: Step 1: Preparation of sulfide all-solid-state mold battery: (A) Positive electrode: The positive electrode material, sulfide solid electrolyte, and nanofiber carbon are placed in an agate mortar in a mass ratio of 85:14:1 and manually mixed for half an hour to ensure thorough mixing, thus obtaining the composite positive electrode material. The weighed composite positive electrode material is placed in a battery mold and pressed into shape under a pressure of 200MPa to obtain the positive electrode sheet.

[0092] (B) Sulfide electrolyte: Li6PS5Cl powder is added into the battery mold and pressed into shape under 150MPa pressure to obtain electrolyte sheet.

[0093] (C) Negative electrode: high-purity indium sheet and lithium copper composite sheet.

[0094] (D) Assemble the battery: Place the Li-Cu sheet in the battery mold in sequence, then place the In sheet, put in the pressed electrolyte sheet, then put the positive electrode sheet into the battery mold, put on the external clamp, press under 150MPa pressure for 2min, and then fix the clamp; start the electrical performance test.

[0095] The electrical performance tests are as follows: (1) Capacity performance test method: a charging test is performed with a small current of 0.1C, and then a discharging test is performed with 0.1C to obtain the 0.1C discharge specific capacity. The quality of capacity performance is determined by comparing the amount of discharge capacity.

[0096] (2) D50 test: The volume median particle size of each cathode material was tested using a laser particle size analyzer.

[0097] (3) Average comprehensive sphericity index test: The average comprehensive sphericity index of the material is obtained according to the method provided in test method 1 above.

[0098] (4) Porosity test: The porosity of the material is obtained according to the method provided in test method 1 above.

[0099] (5) BET test: The porosity of the material is obtained according to the method provided in test method 1 above.

[0100] (6) The positive electrode active material includes closed pores; the closed pores are closed pores located inside the core, and the closed pores are not connected to the outer surface of the particles; the porosity of the closed pores is P. 闭 ;P 闭 Satisfying Formula 10: P 闭 =(1 / ρ 真 -1 / ρ 实 ) / V 表 ×100%, where V 表 ρ represents the apparent volume of the positive electrode active material per unit mass; 真 ρ represents the density of the material as measured by a true density meter. 实 The density, representing the compact state (without any pores) of the material, can be directly obtained from XRD analysis. The test results of the above embodiments are detailed in Table 1.

[0101] Table 1 See the internal structure planar diagram of the positive electrode active material particles prepared in Example 1 of this application. Figure 2 .

[0102] Results Analysis: Based on the experimental results in Table 1, it can be seen that the porosity (OPA) calculation formula and average comprehensive sphericity index (ACS) measurement method provided in this application can establish an effective correlation system from microstructure to macroscopic performance for cathode active materials. Specifically, when the OPA and ACS values ​​of the materials measured according to the method of this application are within the above-mentioned range, the batteries prepared from these materials all exhibit excellent discharge capacity. Therefore, the measurement method provided in this application can accurately reflect the structural characteristics of the materials, and the cathode active materials regulated based on this method can achieve better battery performance. Thus, the cathode active materials with specific OPA and ACS ranges obtained through the technical solution of this application exhibit stable and excellent high-capacity characteristics in battery applications.

[0103] Examples 7 to 10: The difference between Examples 7 to 10 and Example 1 is that, except for the different first sintering temperature in step 2, all other conditions remain the same. See Table 2 below for the differences.

[0104] The experimental test results of Examples 7 to 10 are shown in Table 2.

[0105] Table 2 Results Analysis: Based on the test results in Table 2, a clear correlation exists between the preparation process of the positive electrode active material (first sintering temperature) and the key structural parameters obtained using the porosity (OPA) calculation formula and the average comprehensive sphericity index (ACS) determination method provided in this application. The experimental test results from the embodiments show that adjusting the sintering temperature can affect both the OPA and ACS parameters of the positive electrode active material.

[0106] Therefore, the porosity measurement method, the average comprehensive sphericity index measurement method, and the "structural parameter-battery performance" correlation system provided in this application can not only accurately quantify the key structural features of materials, but more importantly, provide clear and quantifiable guidance for optimizing battery performance through process control. This has practical significance for the controllable preparation and performance optimization of positive electrode active materials for high-performance lithium-ion batteries.

[0107] Example 11: Step 1: Weigh nickel sulfate, cobalt sulfate, and manganese sulfate according to a nickel-cobalt-manganese molar ratio of 85:15:5. Dissolve each of the nickel sulfate, cobalt sulfate, and manganese sulfate separately in deionized water. Stir and mix the metal solutions to obtain a mixed metal solution with a nickel sulfate concentration of 1.7 mol / L, a cobalt sulfate concentration of 0.2 mol / L, and a manganese sulfate concentration of 0.1 mol / L. Prepare 5 mol / L NaOH as a precipitant and ammonia water as a complexing agent. Add the metal solution, precipitant, and complexing agent to the reaction vessel for co-precipitation reaction. The ammonia water concentration is 8.5 g / L, the pH is 11.8, and the water temperature is controlled at 50℃ to obtain the precursor of the cathode material.

[0108] Step 2: Add the cathode material precursor, lithium hydroxide, TiO2, and ZrO2 to a high-speed mixer at a molar ratio of 1.0:0.98:0.003:0.003 and mix at 120 rpm for 50 minutes to obtain a primary mixture. Place the primary mixture into a box-type sintering material for the first sintering. The primary mixture is sintered in an air atmosphere with an oxygen concentration of 80%, a sintering temperature of 800℃, and a sintering time of 10 hours to obtain the first sintered product.

[0109] Step 3: The first sintering product and B2O3 were added to a high-speed mixer at a molar ratio of 1.0:0.001 and mixed for half an hour to obtain a secondary mixture. The secondary mixture was then placed in a box-type sintering material for a second sintering. The second mixture was sintered in an oxygen atmosphere with an oxygen concentration of 90%, a sintering temperature of 350°C, and a sintering time of 6 hours to obtain a high-nickel cathode material. See the planar image of the morphology of the cathode active material particles prepared in Example 11 of this application. Figure 3 .

[0110] Examples 12 to 16: The difference between Examples 12 to 16 and Example 11 is that, except for the different molar ratios of the cathode material precursor, lithium hydroxide, and TiO2 / ZrO2 in step 2, all other conditions remain the same. See Table 3 for the differences. See Table 3 for the experimental results.

[0111] Table 3 Results Analysis: Based on the experimental results in Table 3, it is evident that the ratio of precursor to lithium hydroxide has a systematic impact on the structure and performance of the high-nickel cathode material. With increasing lithium ratio, the material open porosity (OPA) increases accordingly, while the average comprehensive sphericity index (ACS) remains stable, and the battery discharge capacity gradually increases. However, when the lithium ratio increases to a high level, the OPA rises significantly and exceeds a suitable range, resulting in a marked change in the material's structural characteristics. These results demonstrate that the OPA and ACS measurement methods provided in this application can effectively quantify the influence of process parameters on the material structure and establish a clear correlation between them and battery performance, providing a reliable basis for optimizing cathode materials through ratio control.

[0112] Example 17: The preparation process of Example 17 is basically the same as that of Example 16, except that the additives used in step 2 are ZrO2 and WO3, while other conditions remain unchanged.

[0113] Example 18: The preparation process of Example 18 is basically the same as that of Example 16, except that the doping additives in step 2 are ZrO2 and Sb2O3, while other conditions remain unchanged. See Table 4 for the differences. See Table 4 for the experimental results.

[0114] Results Analysis: Table 4 shows that changes in dopant type have a systematic impact on the structure and performance of the high-nickel cathode material. When the dopant contains W, the average comprehensive sphericity index (ACS) decreases, while the open porosity (OPA) increases accordingly. When the dopant contains Sb, the ACS increases, while the OPA decreases accordingly. This indicates that different dopants have differentiated regulatory effects on the open porosity and particle morphology of the material, thus affecting the final electrochemical performance.

[0115] The above results further verify that, regardless of the doping system or preparation process used, the porosity (OPA) calculation formula and the average comprehensive sphericity index (ACS) determination method provided in this application can stably and effectively quantify the key structural parameters of the obtained cathode active material. This determination method demonstrates good universality and reliability, and can establish a unified and comparable quantitative standard for evaluating the microstructural characteristics of materials under different process conditions, thereby providing a scientific basis for optimizing the comprehensive performance of cathode materials through process control.

[0116] Example 19: Step 1: Weigh nickel sulfate, cobalt sulfate, and manganese sulfate according to a nickel-cobalt-manganese molar ratio of 90:5:5. Dissolve each of the nickel sulfate, cobalt sulfate, and manganese sulfate separately in deionized water. Stir and mix the metal solutions to obtain a mixed metal solution with a nickel sulfate concentration of 1.8 mol / L, a cobalt sulfate concentration of 0.1 mol / L, and a manganese sulfate concentration of 0.1 mol / L. Prepare 5 mol / L NaOH as a precipitant and ammonia water as a complexing agent. Add the metal solution, precipitant, and complexing agent simultaneously and continuously to the reactor for a co-precipitation reaction. The ammonia concentration is 8 g / L, the pH is 11.5, and the water temperature is controlled at 50℃ to obtain the precursor of the cathode material.

[0117] Step 2: Add the cathode material precursor, lithium hydroxide and Al2O3 to a high-speed mixer at a molar ratio of 1.0:1.12:0.0015 and mix for 50 minutes at a stirring speed of 120 rpm to obtain a primary mixture. Place the primary mixture into a box-type sintering material for the first sintering. The primary mixture is sintered in an air atmosphere with an oxygen concentration of 85%, a sintering temperature of 700℃ and a sintering time of 8 hours to obtain the first sintered product.

[0118] Step 3: The first sintering product and Nb2O3 are added to a high-speed mixer at a molar ratio of 1.0:0.003 and mixed for half an hour to obtain a secondary mixture. The secondary mixture is then placed in a box-type sintering material for a second sintering. The second mixture is then sintered in air at a temperature of 600°C for 6 hours to obtain a high-nickel cathode material.

[0119] Example 20: The preparation process of Example 20 is basically the same as that of Example 19, except that the sintering temperature is controlled at 695°C in step 2, while other conditions remain unchanged.

[0120] Comparative Examples 1 to 6 The difference between Comparative Examples 1 to 6 and Example 19 is that, except for the first sintering temperature in step 2, all other conditions remain the same. See Table 5 for the differences.

[0121] The experimental test results of Examples 19 to 20 and Comparative Examples 1 to 6 are shown in Table 5.

[0122] Table 5 The morphology planar image of the positive electrode active material particles prepared in Comparative Example 6 of this application is shown below. Figure 4 .

[0123] Results Analysis: Based on the experimental results in Table 5, the porosity (OPA) and average comprehensive sphericity index (ACS) measurement methods provided in this application can effectively quantify and distinguish the influence of different sintering temperatures on the key microstructure of the cathode active material. When the sintering temperature is controlled within a suitable range, and the OPA and ACS values ​​of the cathode active material are within the range described in this application (40%≤OPA≤66%, 0.85≤ACS≤0.98), the prepared battery exhibits a high discharge capacity. However, when the sintering temperature of the comparative example is significantly lower or higher than this suitable range, the OPA value of the obtained cathode active material deviates from the above range, indicating that its microstructure has undergone systematic changes.

[0124] The above results demonstrate that the OPA and ACS determination methods provided in this application can not only accurately quantify the impact of sintering processes on material structure, but more importantly, establish an effective correlation between "process parameters-structural characteristics (OPA / ACS)-battery performance". This provides a scientific and reliable quantitative basis and process guidance for optimizing the comprehensive performance of cathode active materials by precisely controlling the sintering temperature.

[0125] The above description describes some specific embodiments of this application, but in actual applications, the application should not be limited to these embodiments. For those skilled in the art, other modifications and alterations made based on the technical concept of this application should fall within the protection scope of this application.

Claims

1. A method for determining the porosity of a positive electrode active material, characterized in that, The method for determining the porosity includes: The total specific surface area (BET), apparent density (ρ), and average particle size (D) of the equivalent spherical surface area of ​​the positive electrode active material were determined. The specific surface area (ESS) of the positive electrode active material was measured; and, The porosity (OPA) of the positive electrode active material is calculated based on the ESS. The ESS satisfies Formula 1: ESS = 6 / (ACS × ρ × D); The OPA satisfies Formula 2: OPA = (BET - ESS) / BET × 100%; Wherein, BET represents the total specific surface area of ​​the positive electrode active material; The ACS represents the average comprehensive sphericity index of the positive electrode active material.

2. The method for determining the porosity of the positive electrode active material according to claim 1, characterized in that, The testing methods for the ACS include: Obtain scanning electron microscope images and laser particle size distribution data of the positive electrode active material; Based on the laser particle size distribution data, the particle size distribution span of the positive electrode active material was determined. Based on the scanning electron microscope image, the projected area S of the nth particle is obtained. n Perimeter P n minor axis length D n and major axis length L n ; The overall sphericity index CS of the nth particle was determined. n ;as well as, Based on the CS n Measure the ACS; Wherein, the CS n Satisfying Formula 3: CS n =α×YS n +β×K; The YS n Satisfying Formula 4: YS n =(Y n ×R n ) 0.5 ; The Y n Satisfying Formula 5: Y n =4π×S n / (P) n ) 2 ; The R n Satisfying Formula Six: R n =D n / L n ; The K satisfies Formula 7: K = a × e （-b×Span） +c; The Span satisfies Formula 8: Span = (D90 - D10) / D50; The ACS satisfies Formula Nine: ACS = (CS1 + CS2 + CS) n ) / n; Wherein, YS n The sphericity parameter of the normalized image for each particle; K is the sphericity compensation factor for the particles; The Y n Indicates the roundness of the nth particle; The R n This represents the aspect ratio of the nth particle; D10, D50, and D90 are characteristic particle sizes obtained from the laser particle size distribution curve; wherein, D10 represents the particle size corresponding to a cumulative volume distribution of 10%, D50 represents the particle size corresponding to a cumulative volume distribution of 50%, and D90 represents the particle size corresponding to a cumulative volume distribution of 90%. The number of particles is represented by n. The CS1, CS2 to CS n These are the combined sphericity indices for the 1st, 2nd, and nth particles, respectively. e is a natural constant; α and β represent weighting coefficients and satisfy α+β=1; a, b, and c represent model coefficients; α, β, a, b, and c are all determined by calibration using standard samples with known sphericity.

3. A positive electrode active material, characterized in that, The positive electrode active material comprises core-shell structured particles, each particle including a core and a coating layer covering the core; the coating layer has openings; the porosity of the openings is represented by OPA, and the average comprehensive sphericity index of the particles is represented by ACS; The OPA and the ACS satisfy the following conditions: 40% ≤ OPA ≤ 66%; 0.85 ≤ ACS ≤ 0.

98. The OPA is measured using the porosity determination method for the positive electrode active material according to any one of claims 1 to 2.

4. The positive electrode active material according to claim 3, characterized in that, 50%≤OPA≤66%; 0.90≤ACS≤0.

98.

5. The positive electrode active material according to claim 3, characterized in that, The D50 satisfies: 2.0µm≤D50≤6.0µm.

6. The positive electrode active material according to claim 3, characterized in that, The BET satisfies the following condition: 0.3m² / g ≤ BET ≤ 1.5m² / g.

7. The positive electrode active material according to claim 3, characterized in that, The general chemical formula of the positive electrode active material is Li. x Ni y M z O2, wherein M contains at least two elements selected from Co, Mn, Al, Sr, Ti, W, P, Mo, Sn, B, Sb, Nb, Zr, and satisfies 0.9≤x≤1.2, 0≤y≤1, and 0≤z≤1.

8. The positive electrode active material according to claim 3, characterized in that, The positive electrode active material includes closed pores; the closed pores are enclosed pores located inside the core, and the enclosed pores are not connected to the outer surface of the particles; the porosity of the closed pores is P. 闭 The P 闭 ≤3%; The P 闭 Satisfying Formula 10: P 闭 =(1 / p 真 -1 / p 实 ) / V 表 ×100%; Wherein, the V 表 The p represents the apparent volume of the positive electrode active material per unit mass; 真 p represents the true density of the positive electrode active material. 实 This indicates the density of the positive electrode active material when there are no pores.

9. A positive electrode sheet, characterized in that, It includes a current collector and a positive electrode material layer located on the current collector, the positive electrode material layer comprising a positive electrode active material as described in any one of claims 3 to 8.

10. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode, the positive electrode including a current collector and a positive electrode material layer located on the current collector, the positive electrode material layer including a positive electrode active material as described in any one of claims 3 to 8.

Images