Positive electrode material, positive electrode sheet, and secondary battery

Abstract

The present application provides a positive electrode material and a preparation method therefor, a positive electrode sheet, and a secondary battery. The ratio of the number of particles having cracks in the positive electrode material to the total number of particles is 1.5% to 11%, and the average length-diameter ratio M / N of the particles in the positive electrode material satisfies: 1≤M / N≤1.6, wherein M is the length of the longest straight edge of a single particle, and N is the length of the straight edge perpendicular to the midpoint of the longest straight edge. In the present application, by controlling the ratio of the number of particles having cracks in the positive electrode material and the length-diameter ratio of the particles, the cycle performance of the positive electrode material can be improved, the gas production performance can be improved, and it can also be ensured that the material has a good capacity.

Description

Positive electrode materials, positive electrode sheets, and secondary batteries

[0001] This application claims priority to Chinese Patent Application No. 202411940209.6, filed on December 26, 2024, entitled "Positive Electrode Material and Preparation Method Thereof, Positive Electrode Sheet and Secondary Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery cathode material technology, specifically to a cathode material, a cathode sheet, and a secondary battery. Background Technology

[0003] Currently, among the many cathode materials available, ternary cathode materials have become the most widely used cathode material in the lithium-ion battery field due to their advantages of high specific capacity and high voltage platform. However, current cathode materials suffer from drawbacks such as significant gas generation and poor cycle stability during charge-discharge cycling.

[0004] Application content

[0005] In view of this, in order to solve at least one of the above defects, it is necessary to provide a cathode material.

[0006] In addition, it is necessary to provide a method for preparing the aforementioned positive electrode material, as well as a positive electrode sheet and a secondary battery using the aforementioned positive electrode material.

[0007] In a first aspect, embodiments of this application provide a cathode material in which the number of particles with cracks accounts for 1.5% to 11% of the total number of particles, and the average aspect ratio M / N of the particles in the cathode material satisfies: 1 ≤ M / N ≤ 1.6, where M is the length of the longest straight side of a single particle in the electron microscope image of the cathode material, and N is the length of the straight side perpendicular to the midpoint of the longest straight side; the method for testing the ratio of the number of particles with cracks in the cathode material to the total number of particles is as follows: in the cross-sectional SEM image (view at 3000x or higher) of the cathode material, the cross-sections of 300 cathode material particles are randomly selected as samples, and the statistical results obtained are used for calculation.

[0008] Secondly, embodiments of this application provide a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes the positive electrode material as described above.

[0009] Thirdly, embodiments of this application provide a secondary battery, including a positive electrode sheet, wherein the positive electrode sheet includes the positive electrode material as described above.

[0010] The cathode material provided in this application, by controlling the proportion of cracks in the cathode material to be between 1.5% and 11%, can effectively reduce gas generation during battery cycling. Furthermore, by controlling the average aspect ratio (M / N) of individual crystal particles in the cathode material to satisfy 1 ≤ M / N ≤ 1.6, the aspect ratio of crystal particles within this range is relatively low. The roundness of crystal particles with a low aspect ratio helps reduce the specific surface area of ​​the cathode material. A smaller specific surface area helps reduce the direct contact between the cathode material and the electrolyte, thereby reducing the generation of side reactions and improving the long-term cycling performance, high-temperature storage performance, and gas generation performance of the cathode material. Therefore, this application can effectively improve the cycling performance and gas generation performance of the cathode material by controlling the proportion of cracks and the aspect ratio of individual crystal particles, while also ensuring good capacity of the cathode material. Attached Figure Description

[0011] Figure 1 is a cross-sectional schematic diagram of a lithium-ion battery using the cathode material of this application during charging.

[0012] Figure 2 is a cross-sectional schematic diagram of a lithium-ion battery using the cathode material of this application during discharge.

[0013] Figure 3 is a scanning electron microscope (SEM) image of the cathode material of Example 1 of this application at 3000x magnification.

[0014] Figure 4 shows a scanning electron microscope (SEM) image of the cathode material of Comparative Example 1 at 3000x magnification.

[0015] Figure 5 is a cross-sectional SEM image of the cathode material of Embodiment 1 of this application at 5000x magnification.

[0016] Figure 6 shows a cross-sectional SEM image of the cathode material of Comparative Example 1 at 5000x magnification.

[0017] Figure 7 shows the 50-cycle capacity retention curves of the batteries prepared with the cathode materials of Example 1 and Comparative Example 1 of this application.

[0018] Figure 8 is a comparison chart of gas production of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 of this application. Detailed Implementation

[0019] The embodiments of this application are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application; it should be noted that, 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; where there is no conflict, the implementation methods and features of the implementation methods of this application can be combined with each other; many specific details are set forth in the following description to provide a full understanding of this application, and the described implementation methods are only a part of the implementation methods of this application, and not all of the implementation methods.

[0020] Because the existing cathode materials have unsatisfactory cycle life and are prone to gas generation, and the existing solutions have relatively simple means of controlling particles, it is difficult to give full play to the advantages of particles.

[0021] The applicant of this application studied the particle morphology of cathode materials and found that the performance of cathode materials is greatly affected by the number of cracks and the roundness of the particles. When there are too many cracks in the cathode material, the intergranular displacement that easily occurs during cycling will expose new surfaces of the particles. In addition, particles with a large aspect ratio and poor roundness will break during the electrode rolling process, exposing even more new surfaces. These newly exposed surfaces will undergo side reactions with the electrolyte, leading to the deterioration of cycle performance and gas generation performance.

[0022] To this end, this application provides a cathode material in which the number of particles with cracks accounts for 1.5% to 11% of the total number of particles, and the average aspect ratio M / N of a single crystal particle of the cathode material satisfies: 1≤M / N≤1.6, where M is the length of the longest straight side of a single particle in the electron microscope image of the cathode material, and N is the length of the straight side perpendicular to the midpoint of the longest straight side; the method for testing the ratio of the number of particles with cracks to the total number of particles in the cathode material is as follows: in the cross-sectional SEM image (view at 3000x or higher) of the cathode material, the cross-sections of 300 cathode material particles are randomly selected as samples, and the statistical results obtained are used for calculation.

[0023] Firstly, the sources of cracks in cathode materials are mainly cell anisotropy, process control during material crushing, and intergranular displacement after cycling. The cracks in the cathode material of this application primarily originate from cell anisotropy and cracks generated during the crushing process. It should be noted that the cracks in this application refer to cracks with an average size between 0.5 nm and 30 nm. Here, crack size refers to crack width. It can be understood that in a cross-section of the cathode material, cracks typically exhibit a long and thin structure, with the crack extension direction as the length direction, and the crack width perpendicular to the length direction. The maximum distance between the two edges along the crack width direction is the crack size. The method for testing the average crack size is as follows: Cross-sections of 300 cathode material particles are randomly selected, and the average crack size of the particles with cracks is calculated as the average crack size. For example, if 20 out of 300 particles have cracks, the average crack size of these 20 particles is calculated as the average crack size.

[0024] This application controls the proportion of cracks in the cathode material within the range of 1.5% to 11%, which can effectively reduce gas generation in the cathode material during battery cycling. When the proportion of cracks in the cathode material is ≤1.5%, there are too few cracks within the particles, which is not conducive to electrolyte penetration, resulting in low powder compaction density of this type of cathode material, and consequently, low electrode compaction density. When the proportion of cracks in the cathode material is >11%, there are too many crystal cracks, and after this type of cathode material is used to prepare a battery, the gas generation in the battery will be significantly worse during cycling. For example, the proportion of cracks in the cathode material can be 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, or any value within the range of any two of the above values.

[0025] Although this application controls the number of cracks in the cathode material, the cathode material may still break during the rolling process, generating fine powder and leading to gas production. Therefore, this application, while controlling the proportion of cracks in the material, further controls the average aspect ratio M / N of individual particles in the cathode material to satisfy 1 ≤ M / N ≤ 1.6. Particles within this range have a low aspect ratio, which helps reduce the specific surface area of ​​the cathode material. A smaller specific surface area helps reduce the direct contact between the cathode material and the electrolyte, thereby reducing the generation of side reactions and improving the cycle performance of the cathode material. Furthermore, a lower aspect ratio also helps reduce the stress difference between the length and radial directions of the particles during the rolling process, thus reducing the breakage of the cathode material during electrode rolling and improving gas production performance. For example, the aspect ratio of the particles can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or any value within the range of any two of the above values.

[0026] Therefore, by jointly controlling the proportion of cracks and the average aspect ratio of particles in the cathode material within the aforementioned range, this application can effectively improve the cycle stability and cycle performance of the cathode material, and also increase the compaction density of the electrode sheet, giving the cathode material good capacity, while also effectively reducing gas production after the cathode material is made into a battery.

[0027] In some embodiments, in the XRD pattern of the cathode material, the cathode material has diffraction peaks within the range of 44° to 45°, and the full width at half maximum (FWHM) of these diffraction peaks is 0.150° to 0.200°. Within this range, the cell size of the cathode material is moderate, which is beneficial to the capacity utilization of the cathode material. The FWHM range of the XRD diffraction peaks is further 0.155° to 0.175°. Exemplarily, the FWHM of the XRD diffraction peaks can be 0.150°, 0.155°, 0.160°, 0.165°, 0.170°, 0.175°, 0.180°, 0.185°, 0.190°, 0.195°, 0.200°, or any value within the range of any two of the above values.

[0028] In some embodiments, the cathode material is a single-crystal material containing individual particles with the same orientation. These individual particles with the same orientation are primary particles. The cathode material includes multiple primary particles, which have good dispersibility and an average particle size of 1 μm to 6 μm. Primary particles with a particle size within this range are beneficial for fully utilizing the capacity of the cathode material, and the good dispersibility of the primary particles is beneficial for improving the cycle performance of the cathode material. Preferably, the average particle size of the primary particles is 1.5 μm to 3 μm. Exemplarily, the average particle size of the primary particles can be 1 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.1 μm, 2.4 μm, 2.7 μm, 3 μm, 3.1 μm, 3.4 μm, 3.5 μm, 3.7 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, or any value within the range of any two of the above values.

[0029] In some embodiments, in the electron microscope (EM) images of the cathode material, the proportion of crystal particles satisfying 1 ≤ M / N ≤ 1.6 is above 90%. By controlling the aspect ratio of more than 90% of the crystal particles in the material to be within the range of 1 to 1.6, it is beneficial to improve the overall roundness of the particles in the cathode material, thereby further reducing the specific surface area of ​​the cathode material, reducing the generation of side reactions, and thus further improving the long-term cycle performance, high-temperature storage performance, and gas generation performance of the cathode material. For example, the proportion of crystal particles satisfying 1 ≤ M / N ≤ 1.6 in the cathode material can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, etc. It should be noted that the proportion of crystal particles satisfying 1 ≤ M / N ≤ 1.6 in the cathode material here refers to the result calculated by counting the aspect ratio of all single crystal particles completely appearing in the field of view of an EM image of a randomly selected cathode material. A single-crystal grain appearing completely in the field of view of an electron microscope image refers to a single-crystal grain whose outline is fully displayed in the electron microscope image, and whose outline is not covered by other single-crystal grains in the field of view or divided by the boundaries of the electron microscope image. The longest straight edge refers to the diameter line within the circumcircle of the grain whose two ends lie on the outline of the single-crystal grain. A straight edge perpendicular to the midpoint of the longest straight edge refers to a straight edge perpendicular to the midpoint of the longest straight edge whose two ends lie on the outline of the single-crystal grain.

[0030] In some embodiments, the median particle size D of the cathode material V,50 The median particle size is 2μm to 4.5μm. V,50 This indicates the particle size of the material when the cumulative particle size distribution percentage reaches 50% by volume. This application controls the median particle size of the cathode material within the above-mentioned appropriate range. This moderate particle size helps reduce the specific surface area of ​​the particles, minimizing side reactions between the particles and the electrolyte, thereby improving the material's safety and cycle life. Simultaneously, particles within this size range also help reduce internal stress and the risk of electrochemical polarization of lithium ions inside and outside the particles, thus increasing the cathode material's capacity. The minimum particle size D of the cathode material... min <1μm, maximum particle size D max <15μm, where the smallest particle size D in the cathode material is... min Below 1 μm, while the largest particle size D max The particle size is less than 15 μm. The presence of a suitable amount of particles smaller than 1 μm is beneficial for improving the compaction density and capacity of the cathode material. Controlling the maximum particle size to below 15 μm is to reduce the number of large agglomerates, which can negatively impact cycle performance. For example, the median particle size D of the cathode material... V,50It is 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, or any value within the range of any two of the above values.

[0031] In some embodiments, the positive electrode material is 0.8 ≤ (D V,90 -D V,10 ) / D V,50 ≤1.6. D V,10 In particle size distribution, D represents the particle size corresponding to 10% of the total volumetric particle size distribution. In other words, in a particle group, 10% of the particles by volume are smaller than this particle size. Typically, D... V,10 Used to describe finer particles within a particle population. (D) V,90 This represents the particle size at which the cumulative volumetric particle size distribution reaches 90%. In other words, in a particle group, 90% of the particles are smaller than this size. (D) V,90 It is typically used to describe coarser particles within a particle group. (D) V,90 -D V,10 ) / D V,50 This application defines the width of the particle size distribution in the cathode material by controlling 0.8 ≤ (D V,90 -D V,10 ) / D V,50 ≤1.6, the cathode material has a moderate particle size distribution, which can reduce the specific surface area of ​​the particles while maintaining the compaction density of the material, thereby ensuring that the cathode material has excellent cycle performance, storage performance and capacity. For example, the cathode material (D... V,90 -D V,10 ) / D V,50 It can be 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or any value within the range of any two of the above values.

[0032] This application controls the particle size of the cathode material to satisfy: D min <1μm, 2.0μm <D V,50 <4.5μm, D max <15μm, 0.8<(D) V,90 -D V,10 ) / D V,50 <1.6, by ensuring that the particle size distribution of the cathode material is within the above range, the specific surface area of ​​the particles can be reduced while maintaining the compaction density of the material, which is beneficial to ensuring that the cathode material has excellent cycle performance, storage performance and capacity.

[0033] In some embodiments, the specific surface area of ​​the cathode material is 0.1 m². 2 / g~1.6m 2In cathode materials, the crystal particles have a small aspect ratio, are relatively rounded, and have a small specific surface area. A small specific surface area helps reduce direct contact between the cathode material and the electrolyte, thereby reducing side reactions and improving the long-term cycle performance, high-temperature storage performance, and gas generation performance of the cathode material. For example, the specific surface area of ​​the cathode material can be 0.1 m² / g, 0.2 m² / g, or 0.3 m² / g. 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g or any value within the range of any two of the above values. Furthermore, the specific surface area of ​​the cathode material is further 0.6 m². 2 / g~1.2m 2 / g.

[0034] In some embodiments, the oil absorption value of the positive electrode material is 10 mL to 40 mL per 100 grams. An oil absorption value within this range indicates that the positive electrode material has a suitable capacity for adsorbing oily substances. During electrode processing, excessive adsorption of the binder PVDF can be avoided, thereby improving the processing performance of the positive electrode material. For example, the oil absorption value per 100 grams of the positive electrode material can be 10 mL, 15 mL, 20 mL, 25 mL, 30 mL, 35 mL, 40 mL, or any value within the range of any two of the above values.

[0035] In some embodiments, the compaction density of the cathode material under a pressure of 3t is 2.5 g / cm³. 3 ~3.6g / cm 3 By controlling the number of cracks and the aspect ratio of crystal particles in the material, the compaction density of the cathode material powder can be effectively improved. This ensures that the cathode material has a high compaction density after being fabricated into an electrode sheet, thereby increasing the capacity of the cathode material. For example, the compaction density of the cathode material can be 2.5 g / cm³. 3 2.6g / cm 3 2.7g / cm 3 2.8g / cm 3 2.9g / cm 33.0g / cm 3 3.1g / cm 3 3.2g / cm 3 3.3g / cm 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 Or any value within the range formed by any two of the above values.

[0036] In some embodiments, the residual alkali in the cathode material is LiOH < 0.5 wt% and Li₂CO₃ < 0.5 wt%. By controlling the number of cracks and the aspect ratio of the crystal particles in the cathode material, it is beneficial to reduce the specific surface area of ​​the particles while increasing the compaction density of the material, thereby reducing the alkalinity of the material and improving storage performance. At the same time, the reduction of residual alkali on the particle surface effectively enhances the electrochemical activity of the cathode material and ensures the smooth diffusion of lithium ions in the material, thus improving battery performance. Exemplarily, the residual alkali content can be 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.35 wt%, 0.5 wt%, or any value within the range of any two of the above values.

[0037] In some embodiments, the general formula of the positive electrode material is as follows: Li a Ni x Co y N 1-x-y-b Y b O2, wherein 0.95≤a≤1.05, 0.5≤x<1, 0≤y≤0.30, 0.001≤b≤0.01, N element includes at least one of Mn and Al, and Y element includes at least one of Al, Ti, Zr, Sr, Mg, Y, Ba, Cu, W, Nb, La, Ce, Mo, Sn, Ta, and Ca. By doping the cathode material with the above elements, the crystal structure of the cathode material can be optimized, the surface morphology of single crystal particles can be further improved, cracks can be reduced, and the particles can be controlled to have a lower aspect ratio, making the particles more rounded. Furthermore, the structural stability and conductivity of the cathode material can be further improved.

[0038] In some embodiments, the mass percentage of Y element in the cathode material is 0.01wt% to 0.5wt%. For example, the mass percentage of Y element in the cathode material can be 0.01wt%, 0.03wt%, 0.05wt%, 0.08wt%, 0.1wt%, 0.12wt%, 0.15wt%, 0.18wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, or any value within the range of any two of the above values.

[0039] The Y element includes at least the Y1 element, which contains at least one element selected from Zr, Sr, Ba, Ca, etc. Doping these elements into the bulk phase can suppress lithium-nickel mixing and reduce the cell volume change during charging and discharging, thereby effectively suppressing the formation of cracks in the crystal during charging and discharging and improving the material's first coulombic efficiency and discharge capacity.

[0040] The Y element also includes at least the Y2 element, which contains at least one of the elements Al, Ti, Mg, Y, Cu, W, Nb, La, Ce, Mo, Sn, and Ta. When these elements are doped into the bulk phase, they can limit the irregular growth of crystal particles and restrict the formation of particles with excessively large aspect ratios, which is beneficial for the aspect ratio of crystal particles to be 1 to 1.6.

[0041] The cathode material provided in this application, by controlling the proportion of cracks in the cathode material to be between 1.5% and 11%, can effectively reduce gas generation during battery cycling. Furthermore, by controlling the average aspect ratio (M / N) of individual particles in the cathode material to satisfy 1 ≤ M / N ≤ 1.6, the particle aspect ratio within this range is relatively low. Low aspect ratio crystal particles have higher roundness, which helps reduce the specific surface area of ​​the cathode material. A smaller specific surface area helps reduce the direct contact between the cathode material and the electrolyte, thereby reducing the generation of side reactions and improving the long-term cycling performance, high-temperature storage performance, and gas generation performance of the cathode material. Therefore, by jointly controlling the proportion of cracks and the average aspect ratio of particles in the cathode material within the aforementioned ranges, this application can effectively improve the cycling stability and performance of the cathode material, increase the compaction density of the electrode sheet, give the cathode material good capacity, and effectively reduce gas generation after the cathode material is fabricated into a battery.

[0042] It is important to note that the difference between single-crystal cathode materials and polycrystalline cathode materials (i.e., polycrystalline secondary particles) lies in the fact that the smallest particles in polycrystalline secondary particles are formed by the agglomeration of nanoscale primary particles. In contrast, the smallest particles in single-crystal cathode materials are typically micrometer-sized single primary particles. Generally, in addition to EBSD testing, scanning electron microscopy (SEM) and other characterization methods can be used to determine whether the obtained cathode product is a single-crystal material. For example, for single-crystal cathode materials, SEM can characterize the morphology of single-crystal particles, showing that they are generally regular or irregular spherical in shape, with no significant particle agglomeration. EBSD can also characterize the orientation of single-crystal cathode materials. EBSD observation shows that at least one grain has the same color, indicating that at least one grain has the same orientation; grains with the same orientation are single crystals. It is important to clarify that the "single-crystal cathode material" known to those skilled in the art is not a "single crystal" in the strict crystallographic sense. In crystallography, an ideal single crystal refers to a crystal with completely identical arrangement and orientation. However, due to limitations such as impurities, strain, and crystal defects, ideal single crystals are very rare and difficult to produce in the laboratory. Therefore, the single-crystal cathode materials known in the art are actually more "single-crystal-like" cathode materials, which only differ from polycrystalline materials composed of numerous small primary particles in size, exhibiting a large particle size similar to single crystals.

[0043] Understandably, a single grain in this application can be a single particle composed of a primary particle. The aforementioned single-crystal cathode material may also contain a small number of "quasi-secondary particles" formed by the adhesion of several single particles (typically ≤16 single particles). "Primary particle" refers to the smallest particle unit identified when observing cathode active materials using a scanning electron microscope. "Secondary particle" refers to a secondary structure formed by the aggregation of multiple primary particles, exhibiting a relatively rounded spherical morphology. "Quasi-secondary particles" are formed by the adhesion of several single particles. Typically, the particle size of a single particle in these quasi-secondary particles is between 1 μm and 6 μm, and generally, the roundness of "quasi-secondary particles" is lower than that of conventional "secondary particles."

[0044] It should be further clarified that the "single crystal" in "single crystal cathode material" as known to those skilled in the art is not a "single crystal" in the strict sense. In crystallography, an ideal single crystal refers to a crystal with completely identical arrangement and orientation. However, due to limitations caused by impurities, strain, and crystal defects, ideal single crystals are very rare and difficult to produce in a laboratory. Therefore, the single crystal cathode materials known in the art are actually more accurately described as "single crystal-like morphology" cathode materials, which differ from polycrystalline materials composed of numerous small primary particles only in size due to their large particle size resembling single crystals.

[0045] This application also provides a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, an electrode assembly, and an electrolyte / electrolyte. Both the electrode assembly and the electrolyte / electrolyte are located within the casing. The electrode assembly includes a separator, a negative electrode, and a positive electrode, with the separator disposed between the positive and negative electrode. The positive electrode includes the aforementioned positive electrode material.

[0046] Specifically, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes the aforementioned positive electrode material. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, the current collector formed by combining the aforementioned conductive foil and polymer substrate.

[0047] In some embodiments, the outer casing can be a packaging bag sealed with an encapsulating film (such as an aluminum-plastic film), for example, the secondary battery is a pouch battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc.

[0048] In some embodiments, the electrode assembly may be a stacked structure, which is formed by alternating layers of a positive electrode, a separator, and a negative electrode. In other embodiments, the electrode assembly may also be a wound structure, which is formed by winding a positive electrode, a separator, and a negative electrode after they are stacked in sequence.

[0049] In some embodiments, the negative electrode sheet includes a negative current collector and a layer of negative active material disposed on at least one surface of the negative current collector. The negative current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative active material can include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials can be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials can be selected from at least one 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 can also be used. These negative electrode active materials can be used alone or in combination of two or more. The battery provided in this application embodiment has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid electrolyte battery, etc., and there is no limitation here.

[0050] Figures 1 and 2 show schematic diagrams of lithium delithiation and lithium insertion during the charging and discharging processes of a lithium-ion battery prepared using the positive electrode material provided in the embodiments of this application. As shown in Figure 1, when the lithium-ion battery is charging, lithium ions are delithilated from the positive electrode and inserted into the negative electrode; as shown in Figure 2, when the lithium-ion battery is discharging, lithium ions are delithilated from the negative electrode and inserted back into the positive electrode.

[0051] The aforementioned cathode material was used in a coin cell, and the cycle performance of the battery was evaluated. At room temperature (25°C), after 50 cycles at 1C / 1C, the cycle retention rate of the battery was ≥96%. This indicates that the aforementioned cathode material can effectively improve the cycle performance of the battery, and the gas production during the cycle is low, not exceeding 1.4 mL, or even reduced to below 1 mL.

[0052] This application also provides a method for preparing the aforementioned cathode material, specifically including the following steps:

[0053] Step S1: The precursor, lithium salt and additive containing Y element are mixed to form a mixture, and the mixture is sintered once to obtain a sintered product.

[0054] Wherein, Y is selected from at least one of the elements selected from Al, Ti, Zr, Sr, Mg, Y, Ba, Cu, W, Nb, La, Ce, Mo, Sn, Ta, and Ca as an oxide, peroxide, hydroxide, chloride, carbonate, sulfate, phosphate, or combination thereof.

[0055] In some embodiments, the mass percentage of the additive containing element Y is 0.01 wt% to 0.5 wt%, based on the mass of the precursor. Exemplarily, the mass percentage of the additive containing element Y can be 0.01 wt%, 0.03 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.12 wt%, 0.15 wt%, 0.18 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, or any value within the range of any two of the above values.

[0056] The Y element includes at least one Y1 element, which includes at least one element selected from Zr, Sr, Ba, and Ca. Additives containing such elements can act as fluxes. Doping these elements into the bulk phase can suppress lithium-nickel mixing and reduce cell volume changes during charge and discharge, thereby effectively suppressing crystal cracking during charge and discharge and improving the material's initial coulombic efficiency and discharge capacity. Adjusting the amount of this flux component containing Y1 element is beneficial for forming well-dispersed primary particles, appropriately sized grains, and minimal lithium-nickel mixing in lithium nickel cobalt oxide single-crystal cathode materials. Well-dispersed primary particles can form a uniform coating layer, preventing the exposure of new interfaces due to particle breakage during electrode rolling. This avoids newly exposed surface particles of the cathode material directly contacting the electrolyte, suppressing side reactions, which is beneficial for improving the material's initial coulombic efficiency, capacity, structural stability, thermal stability, and long-cycle stability. Based on the mass of the precursor, the mass percentage of the effective element in the flux containing Y1 is 0.01wt% to 0.5wt%, for example, it can be 0.01wt%, 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, or any value within the range of any two of the above values.

[0057] The Y element further includes at least the Y2 element, which may contain at least one of the elements Al, Ti, Mg, Y, Cu, La, Ce, Sn, W, Mo, Nb, and Ta. Additives containing these elements can act as inhibitors. Incorporating these elements into the bulk phase can limit irregular particle growth and the formation of particles with excessively large aspect ratios, thus favoring an aspect ratio of 1–1.6. Adjusting the amount of this inhibitory component (Y2 element) facilitates the formation of well-dispersed primary particles with a smaller aspect ratio in lithium nickel cobalt manganese oxide cathode materials. Cathode materials with a smaller aspect ratio have more regular shapes, preventing particle breakage and exposure of new interfaces during electrode rolling. This avoids direct contact between the newly formed interfaces and the electrolyte, suppressing side reactions. This improves the material's structural stability, thermal stability, long-term cycle performance, and gas generation performance. Based on the mass of the precursor, the mass percentage of the effective element in the inhibitor containing Y2 is 0.01wt% to 0.5wt%, for example, it can be 0.01wt%, 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, or any value within the range of any two of the above values.

[0058] In addition, substances such as CaO2, Na2O2, and KMnO4 can be added to the mixture as oxygen supplements. The purpose is to increase the oxygen partial pressure, which is beneficial for particle growth, inhibits the formation of surface rock salt phase, and improves the initial coulombic efficiency, capacity, structural stability, thermal stability, and long-cycle performance of the cathode material. The mass percentage of these oxygen supplements is 0.01 wt% to 1 wt%, based on the mass of the precursor.

[0059] Step S1 specifically involves applying a pressure of 5 MPa to 50 MPa to the mixture, holding it at that pressure for 1 to 5 minutes, and then subjecting it to a first sintering in an oxygen atmosphere. This first sintering includes two stages: the first stage involves a sintering temperature not exceeding 500℃ (typically 300℃ to 500℃) for 6 to 10 hours, aimed at melting the molten salt and ensuring uniform diffusion of the additives within the mixture. The second stage involves a sintering temperature not exceeding 880℃ (typically 550℃ to 880℃) for 4 to 12 hours, allowing the molten salt to fully react with the precursor in an oxygen atmosphere, which is beneficial for forming single-crystal materials. This two-stage gradient temperature sintering promotes particle formation and controls the number of particle cracks. Within the above range, increasing the temperature and extending the holding time further facilitates the fusion of small particles and micro-powders, reducing the number of particle cracks.

[0060] In some embodiments, the first-stage sintering temperature is further 400°C to 450°C. Exemplarily, this temperature can be 410°C, 420°C, 430°C, 440°C, 450°C, or any value within the range of any two of the above values. The first-stage sintering holding time is further 7h to 9h. Exemplarily, this holding time can be 7h, 8h, 9h, or any value within the range of any two of the above values.

[0061] In some embodiments, the second sintering temperature can be further 700℃~860℃. For example, the second sintering temperature can be 700℃, 720℃, 740℃, 760℃, 780℃, 800℃, 820℃, 840℃, 860℃, 880℃ or any value within the range of any two of the above values. The second sintering holding time can be further 6-10h. For example, the holding time can be 6h, 7h, 8h, 9h, 10h or any value within the range of any two of the above values.

[0062] In some embodiments, the lithium salt in step S1 may include any one or a combination of at least two of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, or lithium oxalate, preferably lithium hydroxide.

[0063] In some embodiments, the mixing method in step S1 is mechanical mixing, which can improve the mixing effect. For example, a high-speed mixer or a VC mixer can be used to mix the materials.

[0064] In some embodiments, the mixing time in step S1 can be 0.3h to 2.0h, and an appropriate mixing time can improve the material dispersion effect. For example, the mixing time can be 0.3h, 0.4h, 0.5h, 0.7h, 0.8h, 1.0h, 1.2h, 1.5h, 2.0h, or any value within the range of any two of the above values.

[0065] In some embodiments, the mixing temperature in step S1 can be between 10°C and 50°C. An appropriate mixing temperature can improve the dispersion of materials. Within this range, the materials can be thoroughly and uniformly mixed while preventing excessively high temperatures from causing side reactions in the mixed raw materials. The mixing temperature can further be between 20°C and 40°C. Exemplarily, the mixing temperature can be 10°C, 15°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, or any value within the range of any two of the above values.

[0066] In some embodiments, in step S1, the lithium content in the lithium salt (i.e., lithium compound) of the sintered material is 0.95 to 1.05 molar ratio relative to the total amount of Ni, Co, and N elements in the precursor. Specifically, the general formula of the precursor can be Ni x Co y N 1-x-y O2, 0.5≤x<1, 0≤y≤0.30, and N element includes at least one of Mn and Al. A lithium content within the aforementioned range reduces Li / Ni cation mixing and prevents excessive residual lithium on the surface of the primary sintering product, which could affect processing and safety performance. The lithium content in the lithium salt is further 0.99–1.02%. For example, the lithium content in the lithium salt can be 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.05, or any value within the range of any two of the above values.

[0067] In some embodiments, sintering in step S1 is carried out in an atmosphere with an oxygen content ≥95%. Sufficient oxygen promotes Ni... 2+ To Ni 3+ The conversion reduces Li / Ni cation mixing and improves the capacity of the cathode material.

[0068] Step S2: The primary sintering product is pulverized, and the pulverized primary sintering product is subjected to secondary sintering. The secondary sintering is a multi-stage gradient temperature sintering process to obtain a secondary sintering product.

[0069] Specifically, the product from the first sintering process is subjected to air jet milling. The resulting material has an aspect ratio of 1–1.4 and a particle size of 1–3 μm. The milled material is then subjected to a second sintering process. The reduced particle size of the milled material improves the dispersibility of the single crystal particles, forming a uniform coating layer and inhibiting direct contact between the electrolyte and the active material. This, in turn, enhances the material's initial coulombic efficiency, capacity, structural stability, thermal stability, and long-term cycling stability.

[0070] The second sintering process is a two-stage process: first a high-temperature sintering at 750℃–980℃ for 8–16 hours, which effectively promotes particle growth. Following the high-temperature sintering, a low-temperature sintering process is performed at 500–900℃ for 3–10 hours, which effectively eliminates lattice stress. Furthermore, the temperature difference between the high and low temperatures is less than 300℃.

[0071] In some embodiments, the temperature of the high-temperature sintering stage is further 800-950°C. Exemplarily, the temperature can be 750°C, 800°C, 830°C, 860°C, 890°C, 920°C, 950°C, 980°C, or any value within the range of any two of the above values.

[0072] In some embodiments, the temperature of the low-temperature sintering stage is further 600-800°C. Exemplarily, the temperature can be 500°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, or any value within the range of any two of the above values.

[0073] This step first controls the temperature and time of the high-temperature sintering stage to achieve lithium-ion embedding, promote crystal growth, control the aspect ratio of crystal particles to be low, make the particles more rounded, and reduce the specific surface area. Then, through-hole control of the temperature and time of low-temperature sintering allows lithium-ion to be further embedded, while also playing an annealing role, effectively eliminating lattice internal stress, repairing micrograin boundaries, and reducing the number of cracks in the cathode material.

[0074] Step S3: The secondary sintering product is pulverized to obtain the pulverized secondary sintering product.

[0075] The average aspect ratio M / N of the positive electrode material particles satisfies: 1≤M / N≤1.6, where M is the length of the longest straight side of a single particle, and N is the length of the straight side perpendicular to the midpoint of the longest straight side.

[0076] Specifically, the secondary sintering product is subjected to air jet milling, the milling process parameters are controlled, the mass of the mill body is controlled to be 10% to 60% of the upper limit of the sample volume that the equipment can process, the milling air pressure is controlled to be 20% to 90% of the upper limit of the equipment pressure, the aspect ratio of the milled crystal particles is 1 to 1.6, and the crystal particle size is 1μm to 6μm.

[0077] In this step, the grinding media volume is 10% to 60% of the equipment's upper limit. For example, if the upper limit for the sample volume processed by a small air jet mill is 3 kg, the grinding media volume is 0.3 kg to 1.8 kg. Within this range, the particles can be evenly dispersed to prevent cracking due to excessive particle collisions, while ensuring the efficiency of air jet milling. The grinding media volume is further 20% to 50% of the equipment's upper limit. Exemplarily, the grinding media volume can be 10%, 20%, 30%, 40%, 50%, or 60% of the equipment's upper limit, or any value within the range of any two of the above values.

[0078] In this step, the pulverizing air pressure is controlled within 20% to 90% of the equipment pressure limit. For example, the upper limit of the pulverizing gas pressure for a small air jet mill is 1 MPa, and the pulverizing gas pressure is 0.2 MPa to 0.9 MPa. Within this range, the pulverizing air pressure is moderate, preventing excessive cracking due to strong collisions caused by excessive pulverizing air pressure, and also preventing insufficient particle collisions due to insufficient pulverizing pressure, resulting in undispersed particles. The pulverizing air pressure is further controlled within 30% to 80% of the equipment pressure limit, and further controlled within 40% to 70% of the equipment pressure limit. Exemplarily, the pulverizing air pressure can be controlled at 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% of the equipment pressure limit, or any value within the range of any two of the above values.

[0079] Step S4: Mix the pulverized secondary sintering product with a coating agent, and sinter the mixture to obtain the cathode material.

[0080] In some embodiments, the sintering temperature can be 250°C to 850°C, and the sintering time can be 4h to 10h. Exemplarily, the sintering temperature can be 250°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 850°C, or any value within the range of any two of the above values, and the sintering time can be 4h, 5h, 6h, 7h, 8h, 9h, 10h, or any value within the range of any two of the above values.

[0081] In some embodiments, the coating agent may include at least one of the following substances: Al2O3, AlOOH, ZrO2, Co3O4, Co(OH)2, CoOOH, TiO2, WO3, Nb2O5, MoO3, etc.

[0082] In some embodiments, the mass ratio of the coating agent to the pulverized secondary sintered product can be 0.05 wt% to 3 wt%. For example, the proportion of the coating agent can be 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, or any value within the range of any two of the above values.

[0083] In the preparation process of the cathode material of this application, firstly, by controlling the flux, oxygen supplement, sintering temperature profile, and gas fragmentation process parameters, the crack ratio of the powder material can be effectively optimized, thereby improving the gas generation performance of the cathode material. Furthermore, based on optimizing the crack ratio of the powder material, by further optimizing the inhibitor and sintering temperature profile, the aspect ratio of the crystal particles can be effectively controlled, reducing the breakage of the cathode material during the electrode rolling process and improving the gas generation performance of the battery.

[0084] The present application's solution will be explained below with reference to embodiments. Those skilled in the art will understand that the following examples are for illustrative purposes only and should not be construed as limiting the present application. Unless otherwise stated, reagents, software, and instruments involved in the following embodiments that are not specifically mentioned are all conventional commercially available products or open-source materials.

[0085] Example 1:

[0086] Step S1, the precursor Ni 0.6 Co 0.1 Mn 0.3 O, lithium source LiOH·H2O, flux SrO, inhibitor H2WO4, and oxygen supplement CaO2 are mixed evenly in a high-speed mixer. Among them, LiOH·H2O and Ni 0.6 Co 0.1 Mn 0.3 The molar ratio of O is 1.03, and the mixtures of SrO, H2WO4, CaO2, and Ni are... 0.6 Co 0.1 Mn 0.3 The mass ratios of O were 0.15 wt%, 0.15 wt%, and 0.15 wt%, respectively.

[0087] The mixture was subjected to a pressure of 50 MPa for 5 min. It was then held at 450 °C for 7 h in an oxygen atmosphere with a furnace pressure of 12 ± 4 Pa, and then heated to 800 °C and held for 8 h to obtain the primary sintered product.

[0088] Step S2: The above-mentioned primary sintered product is subjected to air jet milling using a small air jet mill with a mill volume of 0.6 kg and a milling pressure of 0.4 MPa. The air-jet milled material is then subjected to secondary sintering. The first stage temperature is set to 950℃ and held for 10 h, and the second stage temperature is set to 800℃ and held for 6 h, to obtain the secondary sintered product.

[0089] Step S3: The above-mentioned secondary sintering product is subjected to air jet milling using a small air jet mill. The process parameters of the milling are controlled, the mill volume is controlled to be 0.8 kg, the milling air pressure is controlled to be 0.5 MPa, the aspect ratio of the crystal particles after milling is 1.48, and the average particle size is 2.2 μm, thus obtaining the secondary sintering product after air jet milling.

[0090] Step S4: Mix the secondary sintering product after gas crushing with the coating agent Al2O3. The mass ratio of the coating agent to the secondary sintering product after gas crushing is 0.2wt%. The shearing effect during the mixing process can further reduce the aspect ratio of the single crystal particles. Sinter the mixture at 500℃ for 8 hours in an oxygen atmosphere to obtain Al-coated ternary single crystal material.

[0091] Example 2

[0092] The difference from Example 1 is that in step S1, the mass percentage of SrO is 0.30 wt% based on the mass of the precursor. The other steps are basically the same as in Example 1; please refer to Example 1.

[0093] Example 3

[0094] The difference from Example 1 is that in step S3, the mill volume is 1.6 kg and the pulverizing gas pressure is 0.7 MPa. The other steps are basically the same as in Example 1; please refer to Example 1.

[0095] Example 4

[0096] The difference from Example 1 is that in step S1, the mass percentage of H2WO4 is 0.4 wt% based on the mass of the precursor. The other steps are basically the same as in Example 1; please refer to Example 1.

[0097] Example 5

[0098] The difference from Example 1 is that in step S1, the mass percentage of H2WO4 is 0.05 wt% based on the mass of the precursor. The other steps are basically the same as in Example 1; please refer to Example 1.

[0099] Example 6

[0100] The difference from Example 1 is that in step S1, the sintering process was changed from holding at 450°C for 7 hours to holding at 300°C for 5 hours. The other steps are basically the same as in Example 1; please refer to Example 1.

[0101] Example 7

[0102] The difference from Example 1 is that in step S1, the sintering process was changed from holding at 800°C for 8 hours to holding at 700°C for 6 hours. The other steps are basically the same as in Example 1; please refer to Example 1.

[0103] Example 8

[0104] The difference from Example 1 is that in step S2, the secondary sintering process is changed from holding at 950°C for 10 hours to holding at 920°C for 6 hours. The other steps are basically the same as in Example 1; please refer to Example 1.

[0105] Example 9

[0106] The difference from Example 1 is that in step S2, the second sintering process is changed from holding at 800°C for 6 hours to holding at 600°C for 4 hours. The other steps are basically the same as in Example 1; please refer to Example 1.

[0107] Example 10

[0108] The difference from Example 1 is that in step S1, based on the mass of the precursor, the mass percentage of flux SrO is 0.2wt% and the mass percentage of inhibitor H2WO4 is 0.1wt%; the sintering process in step S2 is as follows: after holding at 945℃ for 9 hours, the temperature is lowered to 820℃ and held for 5 hours.

[0109] The other steps are basically the same as in Example 1. Please refer to Example 1.

[0110] Example 11

[0111] The difference from Example 1 is that in step S1, the precursor is Ni. 0.7 Co 0.1 Mn 0.2 O and LiOH·H2O are replaced with Li2CO3, and the flux SrO is replaced with ZrO2. The other steps are basically the same as in Example 1, please refer to Example 1.

[0112] Example 12

[0113] The difference from Example 1 is that in step S1, the precursor is Ni. 0.8 Co 0.1 Mn 0.1 O, the flux SrO is replaced with ZrO2, and the inhibitor is replaced with MoO3. The other steps are basically the same as in Example 1, please refer to Example 1.

[0114] Example 13

[0115] The difference from Example 1 is that the flux SrO has a mass ratio of 0.3 wt%, and the inhibitor H2WO4 has a mass ratio of 0.5 wt%. The other steps are basically the same as in Example 1, please refer to Example 1.

[0116] Comparative Example 1

[0117] The difference from Example 1 is that SrO is not added in step S1. The other steps are basically the same as in Example 1; please refer to Example 1.

[0118] Comparative Example 2

[0119] The difference from Example 1 is that the airflow pulverization process is not performed in step S3. The other steps are basically the same as in Example 1; please refer to Example 1.

[0120] Comparative Example 3

[0121] The difference from Example 1 is that the pulverizing air pressure in step S3 is controlled at 95% of the upper limit. The other steps are basically the same as in Example 1, please refer to Example 1.

[0122] Comparative Example 4

[0123] The difference from Example 1 is that the mill volume in step S3 is 70% of the upper limit of the equipment. The other steps are basically the same as in Example 1, please refer to Example 1.

[0124] Comparative Example 5

[0125] The difference from Example 1 is that the flux SrO has a mass ratio of 0.05 wt%, and the inhibitor H2WO4 has a mass ratio of 0.05 wt%. The other steps are basically the same as in Example 1, please refer to Example 1.

[0126] Comparative Example 6

[0127] The difference from Example 1 is that the flux SrO has a mass percentage of 0.4 wt%, and the inhibitor H2WO4 has a mass percentage of 0.1 wt%; the holding time of 950℃ for 10 h in step S2 is reduced to 930℃ for 10 h. The other steps are basically the same as in Example 1, please refer to Example 1.

[0128] The performance of the cathode materials obtained in Examples 1-12 and Comparative Examples 1-7 were tested using the following methods.

[0129] 1. Length-to-diameter ratio test:

[0130] Sample preparation: Take the positive electrode material prepared in the above examples and comparative examples, and use a 0.5 mm long conductive adhesive to pick up the material. After the material is picked up, use a rubber bulb to blow the conductive adhesive surface with the material 10 times.

[0131] Electron microscopy: Scanning electron microscope (SEM) was used to conduct tests under an electron beam of 5kV / 10mA. Images with more particles were selected and 10 electron microscope images were taken at 3K magnification.

[0132] Aspect Ratio Test: Using Nano Measure software, the length M of the longest straight side of all single-crystal particles in each electron microscope (EM) image, and the length N of the straight side perpendicular to the midpoint of the longest straight side, are measured. The average aspect ratio of each single-crystal particle is M / N. It should be noted that the percentage of crystal particles in the cathode material satisfying 1 ≤ M / N ≤ 1.6 refers to the aspect ratio of all single-crystal particles completely appearing in the field of view of an EM image of a randomly selected cathode material. A single-crystal particle completely appearing in the field of view means that its outline is fully displayed in the EM image, and its outline is not covered by other single-crystal particles in the field of view or divided by the boundaries of the EM image. It should also be noted that the longest straight side refers to the diameter line with both ends on the outline of the single-crystal particle within the circumcircle of the particle. The straight side perpendicular to the midpoint of the longest straight side refers to a straight line perpendicular to the midpoint of the longest straight side and with both ends on the outline of the single-crystal particle.

[0133] 2. Crack test:

[0134] Test on the percentage of cracked particles in the cathode material: First, take powdered cathode material, mix it with conductive carbon black and binder PVDF (polyvinylidene fluoride) in a mass ratio of 80:10:10, add NMP (N-methylpyrrolidone) to form a uniform slurry, coat it onto aluminum foil, and dry it in an oven to form an electrode sheet. Use this electrode sheet as a sample, and according to the standardized procedure for cross-section sample preparation, use an electron transmission microscope to focus an ion beam into a small-sized ion beam to bombard the surface of the sample to achieve sample exfoliation. Perform scanning electron microscopy (SEM) on the exfoliated sample. Under a field of view of 3k or 5k, the field of view of different regions is statistically analyzed, and the proportion of the number of cathode material particles with cracks to the total number of cathode material particles is counted. The proportion is used to characterize the number of cracks. The test results of this application are statistical results obtained by randomly selecting cross-sections of approximately 300 cathode material particles from the SEM image as samples. SEM testing requires random sampling of the cathode material and random selection of regions. The resulting SEM image should represent the average level of the tested cathode material. Since the electrode sheet is not rolled during the fabrication process in this testing method, the percentage of cracks obtained can be considered as the percentage of cracked particles in the powder state of the cathode material.

[0135] Test on the percentage of cracked positive electrode material particles in the positive electrode sheet: First, take powdered positive electrode material, mix it with conductive carbon black and PVDF (polyvinylidene fluoride) binder at a mass ratio of 80:10:10, add NMP (N-methylpyrrolidone) to form a uniform slurry, coat it onto aluminum foil, dry it in an oven, and roll it under 10 MPa pressure to form an electrode sheet. Use this electrode sheet as a sample, and according to the standardized procedure for cross-section sample preparation, use an electron transmission microscope to focus an ion beam into a small-sized ion beam to bombard the surface of the sample to achieve sample peeling. Perform scanning electron microscopy (SEM) on the peeled sample. Under a field of view of 3k or 5k, the field of view of different regions is statistically analyzed, and the proportion of the number of cracked positive electrode material particles to the total number of positive electrode material particles is counted. The proportion is used to characterize the number of cracks. The test results of this application are statistical results obtained by randomly selecting cross-sections of approximately 300 positive electrode material particles from the SEM image as samples. SEM testing requires random sampling of cathode materials and random selection of regions. The resulting SEM image should be representative of the average level of the tested cathode material.

[0136] 3. XRD testing of cathode materials:

[0137] X-ray diffraction phase analysis (XRD): The cathode material was characterized using a Rigaku X-ray diffractometer (XRD) from Japan. The specific parameters were as follows: scanning range 10°-80°, scanning speed 2° / min, step size 0.005°, and Jade software was used to read parameters such as incident angle (2θ), interplanar spacing (d), and full width at half maximum (FWHM) of the characterized sample.

[0138] 4. Particle size test:

[0139] The average particle size of the single-crystal material was measured using Nano Measurer software. The specific method is as follows: morphology analysis of the single-crystal material was performed using a scanning electron microscope (SEM). Random measurements were taken of particles in the SEM at 3000x magnification using Nano Measurer software. The longer side value was used as the particle size. At least 200 particles were counted, and the average value was taken.

[0140] 5. Compacted density test:

[0141] Using a Carver 4350 tester from the United States, a 1g sample was placed in a mold and pressed with a pressure of 3T for 30s. After pressing, the height was measured and the compaction density was calculated.

[0142] 6. Specific surface area test: The specific surface area of ​​the material was tested using the McMeter 3020 nitrogen adsorption method.

[0143] Pre-treatment of finished product: Weigh the mass of the empty sample tube m1; take 3g of sample, degas it under vacuum at 300℃ for 1h, and weigh the sample tube after cooling to get the mass m2; sample mass m = m2 - m1.

[0144] Sample testing: The sample tube was placed in liquid nitrogen, and the amount of nitrogen adsorbed, V, was measured at 6 relative pressures P / P0 to obtain adsorption isotherms; where P / P0 was set to 0.05 / 0.1 / 0.15 / 0.20 / 0.25 / 0.30.

[0145] Fit the isothermal adsorption curve and calculate the monolayer saturated adsorption capacity Vm based on the slope and intercept; calculate the specific surface area of ​​the cathode material based on Vm.

[0146] 7. Surface residual lithium test:

[0147] The total amount of lithium compounds on the surface of the cathode material was tested using a potentiometric titrator. Specifically, the amount of lithium compounds was calculated by titrating with hydrochloric acid and then converting the amount of hydrochloric acid consumed into the amount of lithium compounds.

[0148] The specific testing method is as follows: Take 5g of positive electrode material and place it in 100ml of water. After magnetic stirring for 10 minutes, filter the solution. Take 20ml of the filtrate and titrate it using an automatic potentiometric titrator with standard hydrochloric acid solution at the equivalence point. Calculate the residual carbonate and hydroxide content in the sample by measuring the amount of standard hydrochloric acid solution consumed. When hydroxide ions are converted to water and carbonate ions are converted to bicarbonate ions, the solution potential changes abruptly, reaching the first jump point. The volume of hydrochloric acid consumed at this point is recorded as V1. When bicarbonate ions are converted to water and carbon dioxide, the solution potential changes abruptly, reaching the second jump point. The volume of hydrochloric acid consumed in this process is recorded as V2. Calculate the carbonate and hydroxide content based on V1 and V2.

[0149] 8. Battery manufacturing and performance testing

[0150] The electrochemical performance of the prepared positive electrode material was evaluated using a coin cell. The specific method is as follows: The positive electrode material, SP, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 93:5:2. NMP was added at a solid content of 50%, and the mixture was prepared into a viscous slurry using a high-speed disperser. This slurry was then uniformly coated onto aluminum foil using a scraper, dried in an oven at 80°C, and rolled to form a positive electrode sheet with a diameter of 14 mm. A 16 mm diameter lithium sheet was used as the negative electrode sheet, a Celgard polyethylene PP film as the separator, and a 1 mol / L LiPF6 carbonate solution (DEC / EC volume ratio 1:1) as the electrolyte. The lithium-ion battery was assembled according to the industrial CR2025 coin cell assembly method in an argon-filled glove box, where the oxygen and moisture content were controlled below 0.5 ppm. At a temperature of 25℃±1℃, the voltage range for charge-discharge cycles is 3.0V to 4.4V, and the initial charge-discharge current is 0.1C (20mAh / g).

[0151] The capacity, first efficiency, and rate performance were tested using the LAND battery testing system at 25℃ and 3.0V-4.4V. The reference capacity was set to 200mA / g, and the current density corresponding to 1C was 200mA / g.

[0152] 9. Gas production performance test:

[0153] The storage gas generation performance of the positive electrode material was evaluated using a basic soft-pack battery. The specific method is as follows: Positive electrode material, PVDF, SP, and CNT were weighed in a mass ratio of 97.0:1.0:1.5:0.5. NMP was added at a solid content of 50% to form a viscous slurry. This slurry was then evenly coated onto aluminum foil using a scraper, dried in an oven at 80℃, and rolled to form 4cm × 8cm positive electrode sheets. Graphite negative electrode material, SP, CMC, and SBR were weighed in a mass ratio of 96:1.0:1.2:1.8, dispersed into a slurry, coated onto copper foil, and cut into 4cm × 8cm negative electrode sheets. The positive and negative electrode sheets were assembled into a basic soft-pack battery with a capacity of 2Ah. After formation, the battery was charged to 50% SOC and then stored in a 60℃ oven for 21 days. The volume difference before and after storage was measured using the water displacement method, which represents the gas generation.

[0154] The test results of the cathode materials of Examples 1-12 and Comparative Examples 1-7 are shown in Tables 1 and 2 below.

[0155] Table 1

[0156] Table 2

[0157] Figures 3 and 4 are SEM images of the cathode materials of Example 1 and Comparative Example 1 at 3000x magnification, respectively. Figure 3 shows that the primary particles of the cathode material obtained in Example 1 are well dispersed and uniform. Figure 4 shows that the primary particles of the cathode material obtained in Comparative Example 1 show significant agglomeration, and some particles are not fully grown. Figures 5 and 6 are SEM images of the cross-sections of the cathode materials of Example 1 and Comparative Example 1 at 5000x magnification, respectively. Figure 5 shows that the cathode material obtained in Example 1 has fewer cracks. Figure 6 shows that the cathode material obtained in Comparative Example 1 has more cracks.

[0158] As shown in Figure 7, the single-crystal cathode material obtained in Example 1 exhibits significantly better cycle performance than Comparative Example 1. Furthermore, Table 1 shows that the batteries prepared from the cathode materials of Examples 1-13 demonstrate significantly better cycle performance than those of Comparative Examples 1-6. Table 1 also shows that the storage gas production of the battery prepared from the single-crystal cathode material obtained in Example 1 is significantly lower than that of Comparative Examples 1-6.

[0159] Examples 1, 11, and 12 adjusted the Ni content in the precursor. Using the preparation method of the embodiments of this application for ternary cathode materials with different nickel contents, it can be ensured that the aspect ratio of the single crystal particles in the cathode material is in the range of 1 to 1.6 (specifically 1.3), the particles are relatively round, and the number of cracks is less than 11%. Single crystal cathode materials that meet the above conditions have good cycle performance. After being prepared into a battery, they can effectively reduce the gas production of the battery and improve the storage performance.

[0160] Compared to Example 1, Example 2 increases the amount of flux added, which can significantly reduce the proportion of cracks in the cathode material, reducing the proportion of cracks from 8.3% in Example 1 to 1.9%, improving the cycle performance of the battery, and reducing the amount of gas produced, which can be reduced from 0.91 mL in Example 1 to 0.76 mL.

[0161] Compared to Example 1, Example 3 increases the mill volume and pulverizing air pressure in step S3, which can effectively disperse the single crystal particles evenly and prevent cracks caused by excessive particle collisions, while also ensuring the efficiency of airflow crushing.

[0162] Compared to Example 1, Example 4 increases the amount of inhibitor added, which can reduce the aspect ratio of the cathode material particles, from 1.42 in Example 1 to 1.13. It can also reduce the proportion of cracks in the cathode material, from 8.3% in Example 1 to 7.8%, thereby improving the cycle performance of the battery and reducing the amount of gas produced.

[0163] Compared to Example 1, Example 5 reduced the amount of inhibitor added, which weakened the inhibitory effect on the crystal growth of the cathode material. Therefore, the aspect ratio of the cathode material particles increased compared to Example 1, and the proportion of particles satisfying 1≤X / Y≤1.6 was less than 90%, resulting in increased gas production and decreased cycle performance.

[0164] Compared to Example 1, Examples 6 and 7 both reduced the sintering temperature in step S1 and shortened the holding time. The fusion of small particles and micro powder was not as sufficient as in Example 1. Therefore, the number of single crystal particle cracks increased in Examples 6 and 7, and the gas production also increased.

[0165] Compared to Example 1, Example 8 reduced the secondary sintering temperature in step S2 and shortened the holding time. The growth time of single crystal particles decreased, the crystal particles were not as well repaired as in Example 1, and the crystal cells were smaller. As a result, the number of cracks in the cathode material of Example 8 increased, the half-peak width was larger, and the gas production increased.

[0166] Compared to Example 1, Example 9 reduced the secondary sintering holding temperature and time in step S2. The lattice stress of the single crystal particles was not effectively eliminated, and the crystal particles were not as well repaired as in Example 1. The number of cracks in the cathode material obtained in Example 9 increased, and the gas production also increased.

[0167] Compared to Example 1, Example 10 increased the flux content, reduced the inhibitor content, and adjusted the sintering temperature and sintering time, which can reduce the number of cracks and reduce the aspect ratio of the cathode material particles, thus achieving optimal cycle performance and the lowest gas production.

[0168] Compared to Example 1, Example 11 increases the nickel content in the precursor, which can improve the capacity of the cathode material while ensuring a low aspect ratio and a low crack ratio, resulting in good cycle performance, high capacity and low gas production of the cathode material.

[0169] Compared to Examples 1 and 11, Example 12 further increases the nickel content and, by combining it with appropriate flux and inhibitors, can further improve the capacity of the cathode material while ensuring a low aspect ratio and a low crack ratio, resulting in good cycle performance, high capacity and low gas production of the cathode material.

[0170] In Comparative Example 1, no flux was added, resulting in a high proportion of cracks (12.6%, exceeding 11%). This significantly reduced the cycle performance of the cathode material and increased gas production. In contrast to Example 1, Comparative Example 2, without airflow pulverization after secondary sintering, also exhibited a high proportion of cracks (13.5%, exceeding 11%) in the cathode material. This resulted in a significant reduction in the cycle performance of the cathode material and a significant increase in gas production.

[0171] Comparative Example 3 increased the crushing gas pressure in step S3. The excessively high crushing gas pressure caused too many collisions between crystal particles, resulting in too many cracks. The crack count was 11.8%, which exceeded 11%, leading to more gas production and poor cycle performance in the prepared battery.

[0172] Comparative Example 4 increased the amount of grinding media in step S3. The excessive amount of grinding media caused too many collisions between crystal particles, resulting in too many cracks. The crack count was 12.0%, which exceeded 11%, leading to more gas production and poor cycle performance in the prepared battery.

[0173] Therefore, compared with Examples 1-13, the number of cracks in the cathode materials in Comparative Examples 1-6 is not in the range of 1.5% to 11%, and the aspect ratio is not in the range of 1 to 1.6. The cycle performance and gas generation performance of the cathode materials are both poor.

[0174] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A positive electrode material, characterized in that, The number of particles with cracks in the positive electrode material is 1.5% to 11% of the total number of particles, and the average aspect ratio M / N of the positive electrode material particles satisfies: 1≤M / N≤1.6; Where M is the length of the longest straight side of a single particle in the electron microscope image of the cathode material, and N is the length of the straight side perpendicular to the midpoint of the longest straight side. The method for testing the ratio of the number of particles with cracks to the total number of particles in the cathode material is as follows: In the cross-sectional SEM image (view at 3000x or higher) of the cathode material, 300 cross-sections of cathode material particles are randomly selected as samples, and the statistical results obtained are used for calculation.

2. The cathode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following characteristics: (1) The ratio of the number of particles with cracks to the total number of particles in the positive electrode material is 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11% or within any two of the above values; (2) The ratio of the number of particles with cracks to the total number of particles in the positive electrode material is 1.5% to 8.3%; (3) The ratio of the number of particles with cracks in the positive electrode material to the total number of particles is 1.5% to 7.8%.

3. The cathode material according to claim 1, characterized in that, In the XRD spectrum of the cathode material, the cathode material has diffraction peaks in the range of 44° to 45°, and the full width at half maximum (FWHM) of the diffraction peaks is 0.150° to 0.200°.

4. The cathode material according to claim 1, characterized in that, The number of particles satisfying 1≤M / N≤1.6 in the electron micrograph of the cathode material shall not be less than 90%.

5. The positive electrode material as described in claim 1, characterized in that, The general formula of the cathode material is as follows: Li a Ni x Co y N 1-x-y-b Y b O2, wherein 0.95≤a≤1.05, 0.5≤x<1, 0≤y≤0.30, 0.001≤b≤0.01, N element includes at least one of Mn and Al, and Y element includes at least one of Al, Ti, Zr, Sr, Mg, Y, Ba, Cu, W, Nb, La, Ce, Mo, Sn, Ta and Ca.

6. The cathode material as described in claim 5, characterized in that, The Y element includes at least Y1 and Y2 elements. The Y1 element includes at least one element selected from Zr, Sr, Ba, and Ca, and the Y2 element includes at least one element selected from Al, Ti, Mg, Y, Cu, W, Nb, La, Ce, Mo, Sn, and Ta.

7. The cathode material as described in claim 5, characterized in that, The mass percentage of the Y element in the cathode material is 0.01 wt% to 0.5 wt%.

8. The positive electrode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following characteristics: (1) The positive electrode material includes a plurality of primary particles, wherein the average particle size of the primary particles is 1 μm to 6 μm; (2) The cathode material is a single crystal material, and the cathode material contains single particles with the same orientation.

9. The positive electrode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following characteristics: (1) The particle size of the cathode material satisfies: D min <1μm; (2)2.0μm<D V,50 <4.5μm; (3)D max <15μm; (4)0.8<(D V,90 -D V,10 ) / D V,50 <1.6。 10. The cathode material according to claim 1, characterized in that, The cathode material also satisfies at least one of the following characteristics: (1) The specific surface area of ​​the positive electrode material is 0.1 m². 2 / g~1.6m 2 / g; (2) The oil absorption value of the positive electrode material is 10 mL to 40 mL per 100 grams.

11. The cathode material according to claim 1, characterized in that, The cathode material also satisfies at least one of the following characteristics: (1) The residual alkali of the positive electrode material satisfies: LiOH ≤ 0.5 wt%, Li2CO3 ≤ 0.5 wt%; (2) The compaction density of the positive electrode material is 2.5 g / cm³. 3 ~3.6g / cm 3 .

12. The cathode material according to claim 1, characterized in that, In the cross-sectional electron micrograph of the cathode material, the average size of the crack is between 0.5 nm and 30 nm.

13. The cathode material according to claim 1, characterized in that, The average aspect ratio M / N of the cathode material particles is 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6 or within any two of the above values.

14. A positive electrode plate, characterized in that, It includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer comprising the positive electrode material as described in any one of claims 1 to 13.

15. A secondary battery, characterized in that, It includes a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode material as described in any one of claims 1 to 13.

Images