Positive electrode material, positive electrode sheet, and secondary battery

Abstract

The present application provides a positive electrode material, a positive electrode sheet, and a secondary battery. The positive electrode material comprises an element M, the element M being selected from at least one of Na, K, Mg, Ca, Sr or Ba. The positive electrode material comprises a plurality of particles. The cross-section of each particle comprises a central region and a surface region, and the cross-section of the particle is tested by means of an energy disperse spectrometer (EDS). The average concentration of the element M in the central region is X1, the average concentration of the element M in the surface region is X2, and X1 and X2 satisfy: 1.2≤X2 / X1≤20. The positive electrode material is determined by means of X-ray diffraction, and the unit cell volume V of the positive electrode material is less than 102.3 Å3. The positive electrode material provided in the present application can achieve improved cycle stability capacity and cycle performance.

Description

Positive electrode material, positive electrode sheet and secondary battery Cross-reference to related applications

[0001] This application claims priority to Chinese patent application filed on December 26, 2024, with application number 202411976431.1 and entitled "Positive electrode material, positive electrode sheet and secondary battery". Technical Field

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

[0003] Lithium-ion batteries possess advantages such as high specific energy, high operating voltage, low self-discharge rate, small size, and light weight, and are widely used in various fields such as portable electronic devices, drones, and electric vehicles. With the rapid development of electric vehicles and electronic devices, the requirements for the energy density, safety, and cycle performance of lithium-ion batteries are becoming increasingly stringent, urgently necessitating improvements to the cathode materials in lithium-ion batteries to enhance their cycle performance. Summary of the Invention

[0004] In view of this, in order to solve at least one of the above defects, this application provides a cathode material that improves the cycle stability capacity and cycle performance of the cathode material.

[0005] In addition, this application also provides a positive electrode sheet using positive electrode materials and a secondary battery.

[0006] This application provides a cathode material comprising element M, which is selected from at least one of Na, K, Mg, Ca, Sr, or Ba. The cathode material comprises multiple particles, each particle having a cross-section including a central region and a surface region. Energy dispersive spectroscopy (EDS) is used to measure the cross-section of the particles. The average concentration of element M in the central region is X1, and the average concentration of element M in the surface region is X2. X1 and X2 satisfy: 1.2 ≤ X2 / X1 ≤ 20. X-ray diffraction is performed on the cathode material to determine the unit cell volume.

[0007] This application also provides 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 a positive electrode material.

[0008] This application also provides a secondary battery, including a casing, an electrode assembly, and an electrolyte or electrolyte solution. The electrode assembly and the electrolyte or electrolyte solution are both located inside the casing. The electrode assembly includes a separator and a negative electrode plate. The electrode assembly also includes a positive electrode plate. The separator is disposed between the positive electrode plate and the negative electrode plate.

[0009] In this application, the concentration of element M in the particles is controlled to satisfy 1.2 ≤ X2 / X1 ≤ 20, resulting in a higher content of element M near the particle surface, which increases the unit cell volume in the particle surface region. Conversely, the content of element M near the particle center is lower, resulting in a relatively smaller unit cell volume in the particle center region. This creates compressive stress from the surface towards the center of the particle. This compressive stress can suppress lattice expansion during charging and discharging, thereby improving gas generation performance and long-term cycle performance. Simultaneously, the cell volume of the cathode material is controlled... Small cell volume means shorter distances between atoms or ions within the cell, which enhances the interaction forces between atoms or ions (such as Coulomb forces and van der Waals forces), thereby increasing the cohesive energy of the crystal. This can further suppress volume changes in the cathode material during charging and discharging, and improve the cycle stability of the cathode material.

[0010] Explanation of main component symbols

[0011] Electrode assembly 100, positive electrode 101, negative electrode 102 and separator 103. Attached Figure Description

[0012] Figure 1 is a cross-sectional schematic diagram of a lithium-ion battery using the cathode material of this application during charging.

[0013] Figure 2 is a cross-sectional schematic diagram of a lithium-ion battery using the cathode material of this application during discharge.

[0014] Figure 3 is a scanning electron microscope (SEM) image of the cathode material of Example 1 of this application.

[0015] Figure 4 is a high-magnification scanning electron microscope (SEM) image of the positive electrode material of Example 1 of this application.

[0016] Figure 5 is a distribution diagram of element M in the cathode material of Example 1 of this application within the particles.

[0017] Figure 6 is a schematic diagram of the concentration distribution of element M in this application.

[0018] Figure 7 is a schematic diagram of the surface and central regions of the elongated particles in 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] One embodiment of this application provides a secondary battery, including a casing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located within the casing.

[0021] The outer casing can be a packaging bag encapsulated with a sealing film (such as aluminum-plastic film), for example, a pouch battery. In other embodiments, it can also be a steel-cased battery, an aluminum-cased battery, etc.

[0022] Referring to Figures 1 and 2, the electrode assembly 100 includes a positive electrode 101, a negative electrode 102, and a separator 103, with the separator 103 disposed between the positive electrode 101 and the negative electrode 102. Referring to Figure 1, during discharge, active ions (such as lithium ions) are deintercalated from the crystal lattice of the negative electrode material in the negative electrode 102, pass through the separator 103 via the electrolyte, reach the positive electrode 101, and embed into the crystal lattice of the positive electrode material (such as a lithium-ion intercalated compound). Electrons are generated and travel from the negative electrode 102 to the positive electrode 101 via an external circuit. The reverse movement of electrons forms a current, which can be used by electrical appliances. During charging, referring to Figure 2, active ions (such as lithium ions) are deintercalated from the crystal lattice of the positive electrode material (such as a lithium-ion intercalated compound) in the positive electrode 101, pass through the separator 103 via the electrolyte, reach the negative electrode 102, and embed into the crystal lattice of the negative electrode material.

[0023] In some embodiments, the electrode assembly 100 may be a stacked structure, which is formed by alternatingly stacking a positive electrode 101, a separator 103, and a negative electrode 102. In other embodiments, the electrode assembly 100 may also be a wound structure, which is formed by sequentially stacking and then winding a positive electrode 101, a separator 103, and a negative electrode 102.

[0024] This application also provides 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 a positive electrode material.

[0025] One embodiment of this application provides a cathode material including element M, which is selected from at least one of Na, K, Mg, Ca, Sr, or Ba. The cathode material includes multiple particles, and the cross-section of each particle includes a central region and a surface region. Energy dispersive spectroscopy (EDS) is used to test the cross-section of the particles. The average concentration of element M in the central region is X1, and the average concentration of element M in the surface region is X2. X1 and X2 satisfy: 1.2 ≤ X2 / X1 ≤ 20. X-ray diffraction is performed on the cathode material to determine the unit cell volume.

[0026] It should be noted that in the cross-sectional view of the particle, within the circumscribed circle of the particle cross-section, the center of the circumscribed circle is taken as the center, and the radius of the circumscribed circle is taken as the radius L of the particle. The region from the center of the particle to a distance L / 2 from the center of the particle is the central region, and the region from the L / 2 position of the particle to the particle surface is the surface region. When the cathode material contains two or more elements M, the X1 and X2 of each element M are measured separately, and the corresponding X2 / X1 values ​​are calculated. Specifically, a cross-sectional sample is prepared using a Hitachi ion cutter (IM5000), a suitable field of view is selected using a Hitachi S4800 scanning electron microscope, and then EDS is used to perform line scanning or spot scanning of the particle cross-section within a 5k field of view. For example, a point scan method can be used to measure the content of element M at 10 locations (generally at least 5 points) in the central region of the particle's cross-section. The summation and averaging of these M content values ​​yields the number of atoms in the central region of the particle (dimensionless). Similarly, the content of element M at 10 locations in the surface region of the particle's cross-section can be measured, and the summation and averaging of these M content values ​​yields the number of atoms in the surface region of the particle (dimensionless). Then, 10 particles are randomly selected, and the number of atoms in the central and surface regions of each particle is characterized using the above method. The summation and averaging of the number of atoms in the central region of each of the 10 particles yields the average concentration X1 (dimensionless) of element M in the central region, and the summation and averaging of the number of atoms in the surface region of each of the 10 particles yields the average concentration X2 (dimensionless) of element M in the surface region.

[0027] It should be further explained that, in this application, in the cross-sectional view of the cathode material, the diameter L of the particle is defined as the diameter of the intersection of the circumscribed circle and the particle's edge. The area covered by the central region of the circumscribed circle is the central region of the particle (i.e., the area from the center of the particle to a distance L / 2 from the center of the particle), and the area covered by the surface region of the circumscribed circle is the surface region of the particle (the area from the position L / 2 of the particle to the particle's surface is the surface region). For irregularly shaped particles, such as elongated particles, as shown in Figure 7, the center of the circumscribed circle is defined as the center of the particle, the diameter L of the particle is defined as the diameter of the particle, the portion of the particle covered by the surface region of the circumscribed circle is the surface region of the particle, and the area covered by the central region of the circumscribed circle is the central region of the particle.

[0028] In this application, the concentration of element M in the particles is controlled to satisfy 1.2 ≤ X2 / X1 ≤ 20, resulting in a higher content of element M near the particle surface, which increases the unit cell volume in the particle surface region. Conversely, the content of element M near the particle center is lower, resulting in a relatively smaller unit cell volume in the particle center region. This creates compressive stress from the particle surface towards the center, which can suppress lattice volume changes during charging and discharging, thereby improving gas generation performance and long-term cycle performance. Simultaneously, the cell volume of the cathode material is controlled... A small cell volume means that the distance between atoms or ions within the cell is shorter, which enhances the interaction forces between atoms or ions (such as Coulomb forces and van der Waals forces), thereby increasing the cohesive energy of the crystal. This can further suppress the lattice volume change of the cathode material during charging and discharging, and improve the cycle stability of the cathode material.

[0029] When X2 / X1 < 1.2, the unit cell volume on the particle surface and inside exhibit a uniform distribution, resulting in a relatively large average unit cell volume. This makes it difficult to form a gradient stress field, leading to compressive stress, which is detrimental to improving the long-term cycle performance of the secondary battery. When X2 / X1 > 20, excessive element M accumulates in the surface region of the particle, occupying lattice lithium sites and affecting lithium-ion transport and diffusion, thus reducing the rate performance of the secondary battery.

[0030] In some embodiments, the ratio of X2 / X1 can be 1.2, 1.5, 2, 5, 7, 9, 10, 12, 14, 15, 16, 18, 20, or any value within the range of any two of the above values. The cell volume V of the positive electrode material can be... Or any value within the range formed by any two of the above values.

[0031] In some embodiments, 5 ≤ X2 / X1 ≤ 15. This can further improve the rate performance and long-term cycle performance of cathode materials.

[0032] In some embodiments, the nickel-lithium mixing ratio of the cathode material is 5% to 8%. Controlling the nickel-lithium mixing ratio within a suitable range allows the cathode material to have good capacity. If the nickel-lithium mixing ratio is greater than 8%, too many lithium positions are occupied by nickel, which degrades the capacity of the cathode material. In some embodiments, the nickel-lithium mixing ratio of the cathode material can be 5%, 5.1%, 5.2%, 5.3%, 5.8%, 6%, 6.2%, 6.3%, 6.5%, 7%, 7.3%, 8%, or any value within the range of any two of the above values.

[0033] In some embodiments, the cell parameter c / a of the cathode material is greater than 4.95. This application further limits the cell parameter c / a value to be greater than 4.95. When the c / a value of the cathode material is within the above range, the cathode material has a suitable interlayer spacing, thereby reducing interlayer stress, improving the stability of the layered structure, which is beneficial for lithium-ion transport and reducing lattice volume changes caused during lithium-ion insertion or extraction. In some embodiments, the cell parameter c / a value of the cathode material can be 4.96, 4.97, 4.99, 5, 5.01, 5.02, 5.03, 5.04, 5.05, or any value within the range of any two of the above values. Preferably, the cell parameter c / a value of the cathode material is greater than 4.95 and less than or equal to 5.05.

[0034] In some embodiments, the unit cell parameters of the cathode material If the cell parameter 'a' of the cathode material is within the above range, it indicates that the distance between atoms within the layers of the cathode material is relatively short. This is beneficial for reducing the cell volume, increasing the cohesive energy of the crystal, suppressing lattice volume changes during charging and discharging, and improving the cycle stability of the cathode material. If the cell parameter 'a' of the cathode material is greater than... This indicates that the distance between atoms within the layers of the cathode material is relatively long, the unit cell volume is large, and the cohesive energy of the crystal is low, which is not conducive to suppressing the lattice volume change of the cathode material during charging and discharging. In some embodiments, the unit cell parameter 'a' of the cathode material can be... Or any value within the range of any two of the above values. Preferably, the cell parameter a of the positive electrode material is greater than or equal to... Less than or equal to

[0035] In some embodiments, the unit cell parameters of the cathode material A smaller cell parameter c indicates a smaller interlayer spacing in the cathode material, which reduces the cell volume, increases the cohesive energy of the crystal, and suppresses lattice volume changes during charge and discharge, thus improving the cycle stability of the cathode material. If the cell parameter c of the cathode material is greater than... This indicates that the large interlayer spacing of the cathode material results in a large cell volume and low crystal cohesive energy, which is detrimental to suppressing lattice volume changes during charging and discharging. In some embodiments, the cell parameter c of the cathode material can be... Or any value within the range formed by any two of the above values. Preferably, the cell parameter c of the positive electrode material is greater than... Less than or equal to

[0036] Therefore, this application can generate compressive stress in the particles of the cathode material by controlling the concentration of element M in the particles to satisfy 1.2≤X2 / X1≤20. Furthermore, by controlling the unit cell volume of the cathode material... Unit cell parameters Furthermore, a cell parameter c / a ratio greater than 4.95 enables the cathode material particles to form a stable crystal structure with high cohesive energy, thereby synergistically forming a stable compressive stress structure, improving the structural stability of the cathode material, suppressing the lattice volume change formed during charging and discharging, and further improving the cycle stability and rate performance of the cathode material.

[0037] In some embodiments, the lattice strain ε of the cathode material is: ε < 0.2%. By controlling the lattice strain of the cathode material within a suitable range, it is beneficial for the crystal to form a stable compressive stress structure, reduce the crystal volume change caused by lithium ion migration during the charging and discharging process of the secondary battery, suppress the generation and diffusion of microcracks within the particles of the cathode material, thereby improving the stability and cycle performance of the cathode material and reducing the DC internal resistance (DCR) of the cathode material. In some embodiments, the lattice strain ε of the cathode material can be 0.05%, 0.07%, 0.1%, 0.12%, 0.15%, 0.18%, or any value within the range of any two of the above values.

[0038] 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 can observe that at least one grain has the same color, indicating that the orientation within a grain is the same; grains with the same orientation are single crystals. It is important to note 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 imposed by impurities, strain, and crystal defects, ideal single crystals are extremely rare and difficult to produce in the laboratory. Therefore, the single-crystal cathode materials known in the art are actually more often "single-crystal-like" cathode materials, which differ from polycrystalline materials composed of numerous small primary particles only in size, exhibiting a large particle size similar to single crystals.

[0039] 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. "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 5 μm, and generally, the roundness of "quasi-secondary particles" is lower than that of conventional "secondary particles."

[0040] In some embodiments, the cathode material is a single-crystal material, and the particles include primary particles with an average particle size of 1 μm to 5 μm. This is beneficial for the cathode material to have good capacity and rate performance, as well as good long-term cycle performance. If the average particle size of the primary particles is small, such as less than 1 μm, the primary particles will agglomerate severely and are prone to breakage during the electrode rolling process, increasing the contact area with the electrolyte, increasing side reactions, and affecting the long-term performance of the battery. If the average particle size of the primary particles is large, such as greater than 5 μm, the average particle size of the primary particles will be large, which will affect the conductivity of the cathode material and the transport of lithium ions, seriously affecting the capacity utilization and rate performance of the cathode material. In some embodiments, the average particle size of the primary particles can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any value within the range of any two of the above values.

[0041] In some embodiments, based on the mass of the cathode material, the concentration of element M is m, where 10 ppm ≤ m ≤ 400 ppm. The concentration of element M within this suitable range is beneficial for ensuring that the cathode material particles contain an appropriate amount of element M and that element M maintains a suitable unit cell volume. The unit cell volume of the particles exhibits a contracted state, reducing cracks generated in the cathode material during long-term cycling, further improving the cycle stability of the cathode material, and simultaneously ensuring good rate performance and cycle performance. In some embodiments, the concentration of element M can be 10 ppm, 50 ppm, 80 ppm, 100 ppm, 120 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, or any value within the range of any two of the above values.

[0042] In some embodiments, the cathode material further includes element N, which is selected from at least one of Zr, Ti, Al, W, Ce, or Y. In the above-described cathode material, doping with an appropriate amount of element N can further improve the specific capacity and cycle stability of the cathode material.

[0043] In some embodiments, the concentration of element N is n, where n < 5000 ppm, based on the mass of the cathode material. In some embodiments, the concentration of element N can be 10 ppm, 100 ppm, 200 ppm, 500 ppm, 600 ppm, 800 ppm, 1000 ppm, 1500 ppm, 1700 ppm, 1900 ppm, 2000 ppm, 2500 ppm, 2700 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 4800 ppm, or any value within the range of any two of the above values. In some embodiments, the concentration of element N is between 1000 ppm and 3000 ppm.

[0044] In some embodiments, the concentration m of element M and the concentration n of element N satisfy: 1 < n / m < 300. When the concentrations of element M and element N satisfy the above relationship, it is beneficial to improve the cycle stability of the cathode material, and it is also beneficial to improve the rate performance and long-term electrochemical performance of the cathode material. When n / m < 1, the concentration of element N is too small to improve the growth of the unit cell volume of the particles and cannot improve the performance of the cathode material; when n / m > 300, the concentration of element N is too high, and too much element N will accumulate on the surface layer of the particles, easily causing agglomeration and adhesion of the particles. During the compaction process of preparing the cathode electrode sheet using the cathode material, it is easy to cause cracking of the agglomerated particles, which will increase the side reaction between the electrolyte and the cathode material in the secondary battery and affect the long-term electrochemical performance of the secondary battery. In some embodiments, n / m can be 1.5, 5, 10, 20, 50, 100, 150, 200, 250, 290 or any value within the range composed of any two of the above values. In some embodiments, preferably, the range of n / m is 5 to 150.

[0045] In some embodiments, in the X-ray energy spectrum of the cathode material, among the three elements Ni, Co, and Mn of the cathode material, the standard deviation of the mass content of each element is less than or equal to 0.03. Such a setting is beneficial to make the Ni, Co, and Mn elements in the cathode material evenly distributed, reduce the structural defects of the particles in the cathode material, and is beneficial to promote the segregation of element M to the surface layer region of the particles, making the concentration of element M in the particles show a distribution structure with a higher concentration in the surface layer region and a lower concentration in the central region. Thereby, it is beneficial to maintain the stability of the compressive stress of the crystal structure, further inhibit the lattice volume change during the charge and discharge process in the cathode material, and inhibit the generation and expansion of cracks. It should be noted that a cross-section sample is prepared using a Hitachi ion milling instrument, then a complete particle cross-section field of view is selected using a Hitachi S4800 scanning electron microscope, and then an X-ray energy spectrometer (EDS) is used to scan and test the Ni, Co, and Mn contents of the cathode material precursor or the cathode material in the field of view at a magnification of 3K. Randomly select 10 points (not less than 3 in the central region and the surface layer region) to statistically analyze the standard deviation and range of the mass content of each element of Ni, Co, and Mn to characterize the uniformity of the distribution of Ni, Co, and Mn elements.

[0046] In some embodiments, the volume particle size distribution Dv50 of the cathode material is 3.0 μm to 5.0 μm. When the volume particle size distribution of the cathode material is within the above range, it is beneficial to make the cathode material maintain good discharge capacity and rate performance and improve the electrochemical performance of the cathode material. In some embodiments, the volume particle size distribution Dv50 of the cathode material can be 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm or any value within the range composed of any two of the above values.

[0047] In some embodiments, the specific surface area of ​​the cathode material is 0.4 m². 2 / g to 0.9m 2 / g. A specific surface area of ​​the cathode material within the above range is beneficial for reducing the contact between the cathode material and the electrolyte, minimizing side reactions, and resulting in good discharge capacity. In some embodiments, the specific surface area of ​​the cathode material can be 0.4m². 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g or any value within the range of any two of the above values.

[0048] In some embodiments, the tap density ρ1 of the positive electrode material is: ρ1 > 2.0 g / cm³ 3 A suitable tap density for the positive electrode material is beneficial for improving the compaction of the electrode sheet containing the positive electrode material, thereby increasing the energy density of the secondary battery. In some embodiments, the tap density of the positive electrode material can be 2.5 g / cm³. 3 3.0g / cm 3 3.5g / cm 3 4.0g / cm 3 4.5g / cm 3 5.0g / cm 3 Or any value within the range formed by any two of the above values.

[0049] In some embodiments, the compacted density ρ2 of the cathode material powder is: ρ2 ≥ 2.8 g / cm³ 3 A suitable powder compaction density for the cathode material is beneficial for further improving the compaction of the electrode sheet containing the cathode material, thereby increasing the energy density of the secondary battery. In some embodiments, the powder compaction density of the cathode material can be 2.8 g / cm³. 3 3.0g / cm 3 3.2g / cm 3 3.8g / cm 3 4g / cm 3 4.5g / cm 3 Or any value within the range formed by any two of the above values.

[0050] In some embodiments, the general formula of the positive electrode material is: Li x Ni a Co b Q c M (1-a-b-c)O2, where 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, a+b+c<1, element M is selected from at least one of Na, K, Mg, Ca, Sr or Ba, and element Q is selected from at least one of Mn and Al. It should be noted that after element M enters the transition metal layer of the cathode material and occupies the site of the main element, element M will increase the interlayer spacing of the transition metal layer, thus increasing the unit cell volume. When element M is enriched near the grain surface, the unit cell volume of the grain surface region will be larger than that of the grain center region. The stress in the grain surface region is greater, resulting in compressive stress towards the grain center, which in turn causes the grain to tend to shrink from the surface towards the grain center.

[0051] This application also provides a method for preparing a cathode material, including the following steps:

[0052] S1. Prepare a mixed salt solution by mixing raw materials containing Ni, Co, and Q elements in a Ni:Co:Mn ratio; then add a salt solution containing the target dopant element M to the mixed solution according to the target doping ratio to obtain a precursor solution. Element M is selected from at least one of Na, K, Mg, Ca, Sr, or Ba. Element Q is selected from at least one of Mn and Al.

[0053] In this step, the raw materials containing Ni, Co, and Q elements, and the salt solution containing element M can be independently selected from at least one of sulfates, chlorides, and nitrates. The nickel salt solution can be selected from at least one of nickel chloride, nickel sulfate, nickel nitrate, nickel carbonate, nickel oxalate, nickel acetate, metal raw materials, and ternary material recycled materials.

[0054] In this step, the molar ratio of Ni:Co:Q in the mixed salt solution is (50–98):(0–20):(0–30), and the content of both Co and Q in the mixed salt solution is not zero. In the precursor solution, the molar percentage of element M is 0.01 mol% to 0.05 mol%.

[0055] S2. The precursor solution prepared in step S1 is used to prepare an oxide precursor by spray pyrolysis, and the oxide precursor is pulverized to a particle size D50 of 2.0 μm to 4.0 μm.

[0056] In this step, the precursor material powder obtained at this particle size is less abundant and more rounded. In the spray pyrolysis method, the precursor solution is atomized and then sequentially passes through a dehydration temperature zone and a pyrolysis temperature zone to obtain the cathode material precursor. The spray pyrolysis atomization flow rate V satisfies: 300L / h < V < 700L / h. The dehydration temperature zone is 300℃~500℃, and the material residence time in the dehydration temperature zone is 2-10s. The pyrolysis temperature zone is 500℃~850℃, and the material residence time in the pyrolysis temperature zone is 2-20s. In the dehydration temperature zone, the mixed solution after spray atomization is rapidly dehydrated, promoting the enrichment of trace element M on the surface of the dehydrated particles. In the pyrolysis temperature zone, the dehydrated particles after spray atomization are finally pyrolyzed into oxide precursor particles. The higher the pyrolysis temperature, the better the uniformity of Ni, Co, and Mn element distribution inside the particles.

[0057] S3. The pulverized oxide precursor is uniformly mixed with the lithium source and the compound containing element N, and then sintered again; the sintered cathode material is subjected to air jet milling, and the milling pressure P satisfies: 200Kpa < P < 500Kpa, and the milling particle size D50 is controlled within 3.0μm to 5.0μm to obtain the material.

[0058] Compounds containing element N can be Zr(NO3)4, ZrCl4, ZrO2, NH4ZrO3, CH4O 10 Zr3, Zr(HPO4)2, Zr(OH)4, Zr(SO4)2, Zr(CH3COO)4, TiO2, Ti2O3, TiCl4, Ti3(PO4)4, Ti(NO3)4, Ti(SO 4)2. AlCl3, Al2O3, Al(OH)3, NaAlO2, C6H9AlO6, AlOOH, Al2(SO4)3, Al(NO3)3, WO2, WO3, Na2WO4, (NH4) 10 (W 12 O 41 At least one of the following: W2O5, Ce(NO3)3, Ce2(SO4)3, Ce2(C2O4)3, C3Ce2O9, Y(C2H3O2)3, Y2O3, YPO4, Y2(CO3)3, Y(NO3)3, and Y2(SO4)3.

[0059] The lithium source is at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium sulfate, lithium chloride, lithium nitrate and lithium oxalate, and the molar ratio of lithium in the lithium source to the total of nickel, cobalt and manganese in the cathode material precursor is 0.98 to 1.10; the primary sintering temperature is 900℃ to 1000℃ and the primary sintering time is 4h to 20h.

[0060] In this step, the particle size is pulverized within a range that corresponds to the precursor D50 particle size range, making it easy to break down the particles.

[0061] S4. The material obtained after crushing in step S3 is uniformly mixed with the coating agent and sintered a second time. The coating agent contains element N. The sintered product is sieved and demagnetized to obtain the positive electrode material.

[0062] A coating agent is coated onto the surface of the cathode material. This process aims to improve the electrochemical performance of the material through coating.

[0063] The coating agent can be Zr(NO3)4, ZrCl4, ZrO2, NH4ZrO3, CH4O 10 Zr3, Zr(HPO4)2, Zr(OH)4, Zr(SO4)2, Zr(CH3COO)4, TiO2, Ti2O3, TiCl4, Ti3(PO4)4, Ti(NO3)4, Ti(SO 4)2. AlCl3, Al2O3, Al(OH)3, NaAlO2, C6H9AlO6, AlOOH, Al2(SO4)3, Al(NO3)3, WO2, WO3, Na2WO4, (NH4) 10 (W 12 O 41 At least one of the following: W2O5, Ce(NO3)3, Ce2(SO4)3, Ce2(C2O4)3, C3Ce2O9, Y(C2H3O2)3, Y2O3, YPO4, Y2(CO3)3, Y(NO3)3, and Y2(SO4)3.

[0064] The secondary sintering temperature is 300℃~600℃, and the secondary sintering time is 4h-20h.

[0065] Negative electrode sheet

[0066] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector.

[0067] Negative current collectors include copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metal, or any combination thereof.

[0068] Negative current collectors include copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metal, or any combination thereof.

[0069] Negative electrode active materials include materials that reversibly insert / deintercalate lithium ions. In some embodiments, the materials that reversibly insert / deintercalate lithium ions include carbon materials. In some embodiments, the carbon material can be any carbon-based negative electrode active material commonly used in lithium-ion rechargeable batteries. In some embodiments, the carbon material includes, but is not limited to: crystalline carbon, amorphous carbon, or mixtures thereof. Crystalline carbon can be amorphous, flake-shaped, flake-shaped, spherical, or fibrous natural or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbides, calcined coke, etc.

[0070] In some embodiments, the negative electrode active material layer includes a negative electrode active material. The specific type of negative electrode active material is not limited and can be selected according to requirements. In some embodiments, the negative electrode active material includes, but is not limited to: lithium metal, structured lithium metal, natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Li-Al alloys or any combination thereof. The silicon-carbon composite refers to a silicon-carbon anode active material containing at least about 5 wt% silicon by weight.

[0071] In some embodiments, the negative electrode active material comprises at least one of artificial graphite, natural graphite, hard carbon, soft carbon, silicon alloy, or silicon oxide.

[0072] When the negative electrode comprises silicon carbide, based on the total weight of the negative electrode active material, the silicon:carbon ratio is approximately 1:10-10:1, and the median particle size Dv50 of the silicon carbide is approximately 0.1 micrometers to 20 micrometers. When the negative electrode comprises an alloy material, the negative electrode active material layer can be formed using methods such as vapor deposition, sputtering, or plating. When the negative electrode comprises lithium metal, the negative electrode active material layer is formed, for example, using a conductive framework with spherical strands and metal particles dispersed in the conductive framework. In some embodiments, the spherical stranded conductive framework may have a porosity of approximately 5% to approximately 85%. In some embodiments, a protective layer may also be provided on the lithium metal negative electrode active material layer.

[0073] In some embodiments, the negative electrode active material layer may include an adhesive and optionally a conductive material. The adhesive enhances the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0074] In some embodiments, the conductive material includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0075] In some embodiments, the current collector includes, but is not limited to: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with a conductive metal, and any combination thereof.

[0076] The negative electrode can be prepared by methods known in the art. For example, the negative electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and then coating the active material composition onto a current collector. In some embodiments, the solvent may include, but is not limited to, water.

[0077] Separating membrane

[0078] The material and shape of the separator used in the secondary battery of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0079] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0080] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic materials. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.

[0081] The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, the polymer material of which is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0082] electrolyte

[0083] According to some embodiments of this application, the electrolyte includes an organic solvent, a lithium salt, and optional additives.

[0084] The organic solvent in the electrolyte of this application may be any organic solvent known in the prior art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte according to this application; it may be any electrolyte known in the prior art. The additives in the electrolyte according to this application may be any additives known in the prior art that can be used as electrolyte additives. In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or ethyl propionate (EP).

[0085] In some embodiments, the organic solvent includes ether solvents, such as at least one selected from 1,3-dioxapentane (DOL) and dimethyl glycol ether (DME). In some embodiments, the lithium salt includes at least one selected from organic lithium salts or inorganic lithium salts. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(fluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one selected from fluoroethylene carbonate and adiponitrile.

[0086] According to some embodiments of this application, the secondary battery of this application includes, but is not limited to, a lithium-ion battery. In some embodiments, the secondary battery includes a lithium-ion battery.

[0087] This application also utilizes secondary batteries in electronic devices to power loads within those devices. The electronic devices described in this application are not particularly limited. In some embodiments, the electronic devices include, but are not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0088] 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.

[0089] Example 1

[0090] In this embodiment, the cathode material is prepared according to the following method:

[0091] (1) Weigh out nickel chloride, cobalt chloride and manganese chloride and add them to water. Prepare a mixed salt solution according to the molar ratio of Ni:Co:Mn = 60:10:30. Add a 0.01 mol% K hydrochloride solution to the mixed salt solution to obtain the precursor solution.

[0092] (2). The precursor solution obtained in step (1) is atomized and then passed through a dehydration temperature zone and a pyrolysis temperature zone to obtain the cathode material precursor (Ni). 0.599 Co 0.1 Mn 0.3 K 0.001 O), wherein the atomization flow rate is 500L / h, the dehydration temperature zone is 500℃, the material residence time in the dehydration temperature zone is 5s, the pyrolysis temperature zone is 650℃, the material residence time in the pyrolysis temperature zone is 8s, the precursor is subjected to air jet milling, the milling air pressure is 0.35kPa, and the precursor pulverized material with a particle size D50=3.77μm is obtained.

[0093] (3) Mix 600g of the precursor pulverized material from step (2) with 252g of lithium carbonate and 2.0g of Y2O3 (dopant), sinter at 970℃ for 20h in an oxygen atmosphere, and then pulverize the sintered product to obtain pulverized material with a particle size D50 = 3.89μm.

[0094] (4). Mix 600g of the pulverized material from step (3) with 1.5g of WO3 (coating material), sinter at 400°C for 20h in an oxygen atmosphere, and then sieve the resulting material to obtain the cathode material.

[0095] Methods for preparing coin cell half-cells:

[0096] The specific procedure is as follows: The positive electrode material, conductive carbon black, and PVDF are weighed in a mass ratio of 93:5:2. N-methyl-2-pyrrolidone (NMP) is added at a solid content of 50%, and the mixture is stirred into a viscous slurry using a high-speed disperser. This slurry is then evenly coated onto aluminum foil using a scraper, dried in an oven at 80°C, rolled, and cut into positive electrode sheets with a diameter of 14 mm. A 16 mm lithium foil is used as the negative electrode, a Celgard polypropylene membrane as the separator, and a 1 mol / L LiPF6 carbonate solution as the electrolyte. The cells are assembled in an argon-filled glove box to obtain a coin cell half-cell.

[0097] Example 2

[0098] Unlike Example 1, the molar percentage of K hydrochloride solution added to the mixed solution in step (1) is 0.003 mol%; the remaining preparation steps are the same as in Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0099] Example 3

[0100] Unlike Example 1, the molar percentage of K hydrochloride solution added to the mixed solution in step (1) is 0.03 mol%; the remaining preparation steps are the same as in Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0101] Example 4

[0102] Unlike Example 1, the pyrolysis temperature range of the spray pyrolysis method in step (2) is 550°C; the remaining preparation steps are the same as in Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0103] Example 5

[0104] Unlike Example 1, the pyrolysis temperature range of the spray pyrolysis method in step (2) is 750°C; the remaining preparation steps are the same as in Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0105] Example 6

[0106] Unlike Example 1, the sintering temperature in step (3) is 955°C; the remaining preparation steps are the same as in Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0107] Example 7

[0108] Unlike Example 1, the sintering temperature in step (3) is 985°C; the remaining preparation steps are the same as in Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0109] Example 8

[0110] Unlike Example 1, in step (1), a mixed hydrochloride solution was prepared according to the molar ratio of Ni:Co:Mn = 50:20:30; in step (3), the sintering temperature was 980℃; the remaining preparation steps were the same as in Example 1. The specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0111] Example 9

[0112] Unlike Example 1, in step (1), a mixed hydrochloric acid solution was prepared according to the molar ratio of Ni:Co:Mn = 70:10:20; in step (3), 600g of cathode material precursor pulverized material, 268g of lithium hydroxide, and 2.0g of Y2O3 (dopant) were uniformly mixed, and the first sintering temperature was 900℃; the remaining preparation steps were the same as in Example 1. The specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0113] Example 10

[0114] Unlike Example 1, in step (1), a mixed hydrochloric acid solution was prepared according to the molar ratio of Ni:Co:Mn = 80:10:10; in step (3), 600g of cathode material precursor pulverized material, 268g of lithium hydroxide, and 2.0g of Y2O3 (dopant) were uniformly mixed, and the first sintering temperature was 740℃; the remaining preparation steps were the same as in Example 1. The specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0115] Example 11

[0116] Unlike Example 1, in step (1), a mixed hydrochloric acid solution was prepared according to the molar ratio of Ni:Co:Mn = 90:6:4; in step (3), 600g of cathode material precursor pulverized material, 268g of lithium hydroxide, and 2.0g of Y2O3 (dopant) were uniformly mixed, and the first sintering temperature was 740℃; the remaining preparation steps were the same as in Example 1. The specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0117] Example 12

[0118] Unlike Example 1, in step (1), a 0.01 mol% Sr hydrochloride solution was added to the mixed solution; the remaining preparation steps were the same as in Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0119] Example 13

[0120] Unlike Example 1, in step (1), a 0.01 mol% Mg hydrochloride solution was added to the mixed solution; the remaining preparation steps were the same as in Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0121] Example 14

[0122] Unlike Example 1, the dopant added in step (3) is ZrO2, and the amount added is 1.8g; the remaining preparation steps are the same as in Example 1. The specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0123] Example 15

[0124] Unlike Example 1, the dopant added in step (3) is Al2O3, and the amount added is 1g; the remaining preparation steps are the same as in Example 1. The specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0125] Example 16

[0126] Unlike Example 1, the molar percentage of K hydrochloride solution added to the mixed solution in step (1) is 0.001 mol%; the remaining preparation steps are the same as in Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0127] Example 17

[0128] Unlike Example 1, the pyrolysis temperature range of the spray pyrolysis method in step (2) is 850°C; the remaining preparation steps are the same as in Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0129] Example 18

[0130] Unlike Example 1, in step (1), a mixed hydrochloride solution was prepared according to the molar ratio of Ni:Co:Al = 60:10:30; the remaining preparation steps were the same as in Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0131]

[0132] Comparative Example 1

[0133] (1) Weigh out nickel chloride, cobalt chloride, and manganese chloride and add them to water to prepare a mixed hydrochloride solution according to the molar ratio of Ni:Co:Mn = 60:10:30. Add the solution to a reactor at 55°C and use 0.01 mol% NaOH and NH3·H2O as precipitating and chelating agents respectively to carry out a co-precipitation reaction for 36 hours to obtain Ni. 0.599 Co 0.1 Mn 0.3 Na 0.001 (OH)2 precursor, the precursor is dried at 80°C for 12 hours, and then dried again at 110°C for 12 hours.

[0134] (2) 600g of the precursor, 262g of lithium carbonate and 2.0g of Y2O3 (dopant) were uniformly mixed and sintered at 970°C for 20h in an oxygen atmosphere. The sintered product was then pulverized to obtain a pulverized material with a particle size D50 of 3.3μm-4.2μm.

[0135] (3) 600g of pulverized material was initially mixed with 1.5g of WO3 (coating agent), and sintered at 400℃ for 20h in an oxygen atmosphere. The resulting material was then sieved to obtain the finished product. The specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0136] Comparative Example 2

[0137] Unlike Comparative Example 1, in step (2), 600g of the precursor, 262g of lithium carbonate, 2.0g of Y2O3 (dopant), and 1g of K(OH) were uniformly mixed; the remaining preparation steps were the same as in Comparative Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0138] Comparative Example 3

[0139] Unlike Example 1, in step (1), the proportion of K added to the mixed hydrochloric acid solution is 0; the remaining preparation steps are the same as in Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0140] Comparative Example 4

[0141] Unlike Example 1, the molar percentage of K hydrochloride solution added in step (1) is 0.05 mol%; the remaining preparation steps are the same as in Example 1. Specific performance parameters of the cathode material are detailed in Tables 1 and 2.

[0142] The performance of the cathode materials prepared in the examples and comparative examples was tested using the following test methods and battery performance test methods.

[0143] Test method:

[0144] 1. The methods for testing the concentrations of element M and the main element are as follows:

[0145] Using an Agilent 5110 ICP-OES instrument, 0.3g of the positive electrode material sample was digested with aqua regia, cooled, and brought to a final volume of 100ml to obtain the mother liquor. The mother liquor was then tested using the Agilent 5110 ICP-OES instrument to determine the content of element M. 1mL of the mother liquor was diluted 100 times to determine the content of the main elements (Li / Ni / Co / Mn).

[0146] The method for testing the concentration distribution of element M is as follows:

[0147] The method for testing the average concentration X1 of element M in the central region and the average concentration X2 of element M in the surface region of cathode material particles is as follows: A cross-sectional sample is prepared using a Hitachi ion cutter (IM5000). A suitable field of view is selected using a Hitachi S4800 scanning electron microscope, and then EDS is used to perform a line scan or spot scan of the particle cross-section within a 5k field of view. For example, a spot scan can be used to measure the content of element M at 10 locations (generally at least 5 points) in the central region of the particle cross-section. The summation and averaging of the element M content yields the number of atoms in the central region of the particle (dimensionless). Similarly, the content of element M at 10 locations in the surface region of the particle cross-section is measured, and the summation and averaging of the element M content yields the number of atoms in the surface region of the particle (dimensionless). Ten particles were randomly selected and the number of atoms in the central region and the number of atoms in the surface region of each particle were characterized using the method described above. The average concentration of element M in the central region X1 (dimensionless) was obtained by summing and averaging the number of atoms in the central region of each of the ten particles. The average concentration of element M in the surface region X2 (dimensionless) was obtained by summing and averaging the number of atoms in the surface region of each of the ten particles.

[0148] As shown in Figure 6, in the cross-sectional view of the particle, within the circumscribed circle of the particle's cross-section, with the center of the circumscribed circle as the center and the radius of the circumscribed circle as the particle's radius L, the region from the particle's center to a distance L / 2 from the particle's center is the central region, and the region from the particle's L / 2 position to the particle's surface is the surface region. When the cathode material contains two or more elements M, the X1 and X2 values ​​of each element M are measured separately, and the corresponding X2 / X1 values ​​are calculated.

[0149] For point scanning and line scanning, please refer to Figure 6 for the following explanation:

[0150] Point scan: Select 5-10 points in the central region (inside the dashed circle in Figure 6) for EDS measurement, and take the average value to obtain the average number of atoms in the central region X1; select 5-10 points in the surface region (outside the dashed circle in Figure 6) for EDS measurement, and take the average value to obtain the average number of atoms in the surface region X2.

[0151] Line scan: At least three line positions are randomly selected in the central region (i.e., inside the dashed circle in Figure 6) for line scanning. The average value of the measurements is taken to obtain the average number of atoms in the central region X1. At least three line positions are randomly selected in the surface region (i.e., outside the dashed circle in Figure 6) for line scanning. The average value of the measurements is taken to obtain the average number of atoms in the surface region X2. In actual testing, spot scanning and line scanning can also be used in combination.

[0152] 2. The methods for testing the mass content of Ni, Co, and Mn elements are as follows:

[0153] The cross-section samples were prepared using a Hitachi ion cutter. Then, the field of view of the completed particle cross-section was selected using a Hitachi S4800 scanning electron microscope. Finally, the Ni, Co, and Mn contents of the cathode material precursor or cathode material were scanned at 3K magnification using an X-ray energy dispersive spectroscopy (EDS) instrument at 10 randomly selected points (no less than 3 points in the central region and no less than 3 points in the surface region). The standard deviation and range of the mass content of each element Ni, Co, and Mn were statistically analyzed to characterize the uniformity of the distribution of Ni, Co, and Mn elements.

[0154] 3. The methods for testing cell volume, cell parameters (a, c), lithium-nickel hybridization, lattice strain, and grain size are as follows:

[0155] The XRD diffractometer was used to test the XRD pattern in the range of 10°-70° with a speed of 1° / min and a step size of 0.005°. The XRD pattern was then refined by Rietveld using GASA to obtain information such as cell volume, cell parameters (a, c), lithium-nickel mixing, grain size and peak shape parameters. The lattice strain was calculated based on the obtained peak shape parameters according to equation (1).

[0156] Equation (1):

[0157] Where β is the full width at half maximum (FWHM), θ is the diffraction angle (both in radians), k is a constant of 0.89, λ is the X-ray wavelength of 0.154 nm, D is the grain size (in nm), and ε is the lattice strain, which is dimensionless.

[0158] 4. The volumetric particle size D50 test method for cathode materials is as follows: The particle size of the material is tested using a Malvern MS 3000 laser particle size analyzer; the specific method is as follows: Take an appropriate amount of sample, pour it into pure water for ultrasonic dispersion, the ultrasonic time is 30s, the ultrasonic power is 240w, then add an appropriate amount of sodium hexametaphosphate to the dispersed sample, stir evenly, pour it into the sample cell of the detection equipment, wait for 10s, and then click to start the sample test.

[0159] 5. The specific surface area test method is as follows:

[0160] Specific surface area was measured using a McMurray surface area analyzer (USA). The specific method was as follows: the mass of the empty sample tube was weighed (m1); 3g of sample was added to the sample tube through a long-necked funnel, and the tube was degassed under vacuum at 300℃ for 1 hour. After cooling, the mass of the sample tube was weighed (m2); the sample mass was calculated as m = m2 - m1. The sample tube was placed in liquid nitrogen, and the nitrogen adsorption capacity (V) was measured under a series of relative pressures (P / P0) to obtain adsorption isotherms. P / P0 was set to 0.05 / 0.1 / 0.15 / 0.20 / 0.25 / 0.30. The isothermal adsorption curves were fitted, and the monolayer saturated adsorption capacity (Vm) was calculated based on the slope and intercept. The specific surface area was then calculated based on Vm.

[0161] 6. The tap density test method is as follows:

[0162] The tap density was tested using a Canta tap density meter: vibration frequency 260 times / min, vibration number 3000 times, vibration amplitude 3mm±0.1mm, and sample mass in a 23-25ml measuring cylinder.

[0163] 7. The method for testing the compacted density of powder is as follows:

[0164] Using a Carver 4350 tester from the United States, 1g of sample was placed in a mold and pressed with a pressure of 6t for 30s. After pressing, the height was measured and the compaction density was calculated. The compaction density is the ratio of the sample mass to the volume after compaction.

[0165] 8. The method for testing the average particle size of primary particles is as follows:

[0166] SEM images of the cathode material were randomly selected and taken using a Hitachi S4800 scanning electron microscope at a magnification of 3kx, with at least 200 particles per image. The SEM images were opened using Nano Measure software, and particles in the 3000x view were randomly measured. The diameter of the circumcircle of the particle fully exposed in the field of view was taken as the particle size. At least 200 particles were counted, and the average value was taken as the average value of the particles in a single image. A single-crystal particle fully exposed in the electron microscope image is defined as one whose outline is completely displayed in the image, without being obscured by other single-crystal particles or divided by the boundaries of the electron microscope image.

[0167] 9. Electrochemical performance testing:

[0168] a. Sample preparation for electrochemical performance testing:

[0169] Button battery making:

[0170] ① Ingredients: NCM:SP:5% PVDF adhesive = 93:5:2 = 9.3g:0.5g:4.0g, NMP = 9g, stir at high speed to disperse evenly.

[0171] ② Coating and drying: Coat the slurry evenly on a 20μm thick aluminum foil using a 210µm coater, setting the coating length to the maximum length of the coater. Cut off the second half of the electrode and place it in a 100℃ forced-air drying oven to dry for more than 1.5 hours.

[0172] ③ Rolling, punching and drying: During rolling, adjust the roller mill to 1 roll gap and roll 3 times; use a 14mm punching machine to punch holes, weigh, and then put it into a vacuum drying oven to vacuum dry at 85℃ for more than 8 hours.

[0173] ④ Button cell (LIR2016) assembly: Positive electrode shell - 2 drops of electrolyte - Positive electrode sheet (14mm) - 3 drops of electrolyte - 20μm separator - 2 drops of electrolyte Lithium foil - 150μm nickel foam - negative electrode shell (dried at 50℃), the battery is assembled and sealed, and then taken out of the glove box for testing.

[0174] b. Testing of button cells:

[0175] After standing for 12 hours, perform battery testing according to the following procedure:

[0176] The cathode materials prepared in Examples 1-7, Examples 12-18, and Comparative Examples 1-4 were tested at voltages of 3-4.4V; the cathode material prepared in Example 8 was tested at voltages of 3-4.45V; the cathode material prepared in Example 9 was tested at voltages of 3-4.3V; and the cathode materials prepared in Examples 10 / 11 were tested at voltages of 3-4.25V.

[0177] The capacitor was charged at 0.1C and discharged at 0.1C for two cycles, with a constant voltage cutoff current of 0.005C. The first-cycle capacity and the first-cycle coulombic efficiency were measured.

[0178] Charge at 0.5C and discharge at 2C for one cycle, with a constant voltage cutoff current of 0.05C. The ratio of the measured capacity to the capacity of the first cycle is the 2C capacity retention rate.

[0179] The circuit is charged at 0.5C and discharged at 1C for 50 cycles, with a constant voltage cutoff current of 0.05C. The ratio of the measured capacity to the capacity of the first cycle is the 50-cycle capacity retention rate.

[0180] Charge the battery at 0.1C and discharge it at 0.1C until it reaches 3.7V. After letting it stand for 5 hours, place the battery at 25°C and then discharge it at 2C for 30 seconds. Take a sample every 0.1 seconds and calculate the average internal resistance (DCR) over 30 seconds.

[0181] Table 1

[0182] Table 2

[0183] Table 3

[0184] As can be seen from Tables 1 to 3 above, compared with Comparative Examples 1 to 4, in Examples 1 to 18, when the concentration of element M X2 / X1 in the prepared cathode material meets a specific range and the cell volume V of the particles meets a specific range, the cathode material has good specific capacity and low DC internal resistance, as well as excellent first-cycle capacity, first-cycle coulombic efficiency and cycle capacity retention.

[0185] Compared to Example 1, Comparative Example 1 used a co-precipitation method to prepare the cathode material precursor. The obtained cathode material was characterized, and its cell volume was [missing information]. Meanwhile, in Comparative Example 1, no element M was doped, resulting in a higher DC internal resistance of the cathode material and lower initial efficiency and cycle stability.

[0186] Compared with Example 1, Comparative Example 2 uses a co-precipitation method to prepare the cathode material precursor, and K element solid-phase doping is carried out in step (3). The obtained cathode material is characterized by a more uniform distribution of K element inside the cathode material particles, higher DC internal resistance, and lower first-efficiency and cycle stability.

[0187] Compared with Example 1, Comparative Example 3 uses spray treatment and pyrolysis treatment to prepare the cathode material precursor. No K element was added in step (1). The cell volume of the cathode material is larger, the DC internal resistance of the cathode material is higher, and the first efficiency and cycle stability are lower.

[0188] Compared with Example 1, Comparative Example 4 uses spray treatment and pyrolysis treatment to prepare the cathode material precursor. Soluble K salt is added in step (1), and the amount of soluble K salt added in step (1) is increased to 0.05 mol%. Characterization of the obtained cathode material shows that the concentration of K element in the surface and central regions of the cathode material particles is relatively high, the cell volume in the cathode material is large, the DC internal resistance of the cathode material is high, and the first efficiency and cycle stability are low.

[0189] Referring to Figures 3 and 4, the scanning electron microscope (SEM) images and high-magnification cross-sectional SEM images of the cathode material prepared in Example 1 show that the particles are uniformly distributed. Referring also to Figure 5, the content of element M differs between the surface and central regions within the particles.

[0190] 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 by, The cathode material includes element M, which is selected from at least one of Na, K, Mg, Ca, Sr, or Ba. The cathode material comprises multiple particles, each particle having a cross-section including a central region and a surface region. The cross-section of the particles is measured using an energy dispersive spectroscopy (EDS) instrument. The average concentration of element M in the central region is X1, and the average concentration of element M in the surface region is X2. X1 and X2 satisfy the condition: 1.2 ≤ X2 / X1 ≤ 20. X-ray diffraction is performed on the cathode material to determine its unit cell volume.

2. The positive electrode material of claim 1, wherein, The cathode material satisfies any one of the following conditions: (1) 5 ≤ X2 / X1 ≤ 15; (2) 1.2 ≤ X2 / X1 ≤ 5; (3) 15 ≤ X2 / X1 ≤ 20; (4) The ratio of X2 / X1 can be 1.2, 1.5, 2, 5, 7, 9, 10, 12, 14, 15, 16, 18, 20 or within any range of the two values ​​listed above.

3. The positive electrode material of claim 1, wherein, The cathode material satisfies at least one of the following conditions: (1) The lattice strain ε of the cathode material is ε < 0.2%; (2) The lithium-nickel mixing rate of the cathode material is 5% to 8%; (3) the lattice parameter of the positive electrode material 4. The positive electrode material as described in claim 1, characterized in that, Based on the mass of the cathode material, the concentration of element M is m, where 10ppm≤m≤400ppm.

5. The cathode material of claim 1, wherein, The cathode material is a single-crystal material, and the particles include primary particles with an average particle size of 1 μm to 5 μm.

6. The cathode material of claim 1, wherein, The cathode material also includes the elements Ni, Co, and Mn. In the X-ray energy spectrum of the cathode material, the standard deviation of the mass content of each element Ni, Co, and Mn in the cathode material is less than or equal to 0.

03.

7. The cathode material of claim 1, wherein, The cathode material satisfies at least one of the following conditions: (1) The volumetric particle size distribution Dv50 of the cathode material is 3.0 μm to 5.0 μm; (2) the specific surface area of the positive electrode material is 0.4 m 2 / g to 0.9 m 2 / g.

8. The cathode material of claim 1, wherein, The general formula of the cathode material is: Li x Ni a Co b Q c M (1-a-b-c) O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, a+b+c<1, wherein the element M is selected from at least one of Na, K, Mg, Ca, Sr or Ba, and the element Q is selected from at least one of Mn and Al.

9. The cathode material of claim 1, wherein, The unit cell volume of the cathode material satisfies at least one of the following conditions: (1) (2) (3) The unit cell volume V of the positive electrode material can be Or within the range of any two of the above values.

10. The cathode material of claim 1, wherein, The cathode material satisfies at least one of the following conditions: (1) the lattice parameter of the positive electrode material (2) The value of the cell parameter c / a of the cathode material is greater than 4.

95.

11. The cathode material of claim 1, wherein, The cathode material satisfies at least one of the following conditions: (1) the tap density p1 of the positive electrode material: p1 > 2.0 g / cm3 3 ; (2) the powder compaction density p2 of the positive electrode material: p2≥2.8 g / cm3 3 .

12. The cathode material of claim 1, wherein, The cathode material further includes element N, which is selected from at least one of Zr, Ti, Al, W, Ce or Y. The concentration of element N is n based on the mass of the cathode material, where n < 5000 ppm.

13. The cathode material of claim 12, wherein, The concentrations m of element M and n of element N in the cathode material satisfy: 1 <n / m<300。 14. A positive electrode sheet characterized by comprising: The positive electrode sheet comprises the positive electrode material as described in any one of claims 1 to 13.

15. A secondary battery, comprising a positive electrode sheet as described in claim 14 or comprising a positive electrode material as described in claims 1 to 13.

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