Positive electrode material, positive electrode sheet, and battery

Abstract

The present application provides a positive electrode material and a battery. In the positive electrode material, the surface enrichment degree of sulfur element is β=A2 / A1, wherein β≤70%, A1 is the total mass content of sulfur element in the positive electrode material, and A2 is the mass content of sulfur element in free sulfate radicals of the positive electrode material. In a scanning electron microscope (SEM) image of the positive electrode material, the number proportion of particles having a particle size of less than 1 μm in the positive electrode material is 6% to 18%. The positive electrode material of the present application can reduce lattice rotation of the positive electrode material, thereby improving the structural stability and cycle performance of the positive electrode material.

Description

Positive electrode materials, positive electrode sheets and batteries Cross-reference of related applications

[0001] This application claims priority to Chinese patent application filed on December 26, 2024, with application number 202411962899.5 and entitled "Cathode Material and Battery". Technical Field

[0002] This invention belongs to the field of cathode material technology, and particularly relates to cathode materials, cathode sheets and batteries. Background Technology

[0003] Lithium-ion batteries are widely used in laptops, mobile phones, and digital products due to their high energy density, good safety performance, long cycle life, and environmental friendliness. However, the development of cathode materials has been slower compared to the development of high-capacity anode materials (approximately 800-1000 mAh / g). Therefore, researchers are currently focusing their efforts on developing high-capacity and high-voltage cathode materials to improve the energy density of lithium-ion batteries. Cathode materials are the core component in battery development. However, as the capacity of cathode materials increases, problems such as reduced cycle life and poor structural stability also arise.

[0004] Therefore, improving the cycle stability of cathode materials remains an urgent problem to be solved. Summary of the Invention

[0005] This application provides a cathode material, a cathode sheet, and a battery. The cathode material of this application can reduce the lattice rotation of the cathode material, thereby improving the structural stability and cycle performance of the cathode material.

[0006] In a first aspect, this application provides a cathode material in which the surface enrichment of sulfur element is β=A2 / A1, β≤70%, A1 is the total mass content of sulfur element in the cathode material, and A2 is the mass content of sulfur element in the free sulfate ions of the cathode material;

[0007] In the scanning electron microscope (SEM) image of the cathode material, the proportion of particles with a diameter of less than 1 μm is 6% to 18%.

[0008] Secondly, this application provides a positive electrode sheet, the positive electrode sheet comprising the positive electrode material described in the first aspect.

[0009] Thirdly, this application provides a battery, the battery comprising the positive electrode material described in the first aspect or the positive electrode sheet described in the second aspect.

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] The cathode material provided in this application reduces the side reactions between the cathode material and the electrolyte by controlling the proportion of particles with a diameter of less than 1 μm in the cathode material to be 6% to 18%, thereby improving the cycle stability of the cathode material. Furthermore, by controlling the surface enrichment of sulfur element in the cathode material to ≤70%, this application further suppresses the structural damage caused by the side reactions of the cathode material, thereby further improving the structural stability and long cycle performance of the cathode material. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 is a schematic diagram of the discharge state of the battery provided in the embodiment of this application. Detailed Implementation

[0014] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0015] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0016] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0017] For ease of understanding of this invention, specific terms have been appropriately defined in this application. Unless otherwise defined herein, the scientific and technical terms used in this invention have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains.

[0018] This application provides a cathode material; the surface enrichment of sulfur in the cathode material is β=A2 / A1, β≤70%, A1 is the total mass content of sulfur in the cathode material, and A2 is the mass content of sulfur in the free sulfate ions of the cathode material;

[0019] In the scanning electron microscope (SEM) image of the cathode material, the proportion of particles with a diameter of less than 1 μm is 6% to 18%.

[0020] Because particles smaller than 1 μm have extremely high reactivity, the cathode material provided in this application reduces side reactions between the cathode material and the electrolyte by controlling the proportion of particles smaller than 1 μm in the cathode material to be 6%–18%, thereby improving the cycle stability of the cathode material. Furthermore, by controlling the surface enrichment of sulfur in the cathode material to ≤70%, this application further suppresses structural damage caused by side reactions, thereby further improving the structural stability and long-cycle performance of the cathode material. It should be noted that the ratio of A1 to A2 can characterize the degree of sulfur enrichment on the surface of the cathode material. A larger ratio of A1 to A2 indicates a higher sulfur content on the surface of the cathode material, indicating that sulfur is enriched on the surface; a smaller ratio of A1 to A2 indicates a lower sulfur content on the surface of the cathode material and a higher sulfur content in the bulk phase. Wherein, A1 is the total mass content of sulfur in the cathode material, and A2 is the mass content of sulfur in the free sulfate ions of the cathode material. The inventors hypothesize that this is because some sulfur atoms are doped into the lattice of the cathode material and replace oxygen atoms in the layered structure of the cathode material. Appropriate sulfur doping can increase the migration rate of lithium ions, suppress heterogeneous reactions, reduce lattice rotation, and improve the structural stability of the cathode material. Simultaneously, after some sulfur atoms are doped into the lattice, they can connect with oxygen atoms in the lattice through transition metal atoms (such as Ni, Co, Mn, etc.) to form stronger chemical bonds. This enhances the cathode material's tolerance to lattice deformation, alleviates the generation of internal cracks and irreversible phase transitions in the cathode material particles, and improves the cycle stability of the cathode material. In this application, controlling the proportion of particles smaller than 1 μm while controlling sulfur doping can reduce side reactions between the cathode material and the electrolyte, improve the cycle performance of the cathode material, and simultaneously suppress lattice rotation, improving the structural stability of the cathode material and further reducing structural damage caused by side reactions. Under the synergistic effect of these two factors, the cathode material can possess excellent structural stability and long cycle performance.

[0021] It should be noted that the mass content of sulfur in the free sulfate ions of the cathode material is A2. It should be noted that sulfur accounts for 1 / 3 of the mass of sulfate. In this application, 0.5 g of sample was weighed and dissolved in 50 ml of pure water, sonicated for 5 min, filtered, and the free SO4 in the filtrate was measured by ion chromatography. 2- The mass content of ions is a2. The total mass content A1 of sulfur in the cathode material was tested by inductively coupled plasma optical emission spectrometry. Specifically, 0.3g of sample was digested with aqua regia, cooled and brought to a constant volume, and the total mass content A1 of S was tested by inductively coupled plasma optical emission spectrometry (Agilent 5110 ICP-OES).

[0022] In some embodiments, the total mass content of sulfur in the cathode material is Al, 50ppm≤A1≤1000ppm; specifically, it can be 50ppm, 70ppm, 100ppm, 150ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, or 1000ppm, etc., and of course, other values ​​within the above range are also possible, without limitation. The presence of an appropriate amount of S in the cathode material can improve the migration rate of lithium ions, suppress heterogeneous reactions, reduce lattice rotation in the cathode material, and enhance the structural stability of the cathode material. When the total mass content of sulfur in the cathode material is too high, the capacity of the cathode material decreases. When the total mass content of sulfur in the cathode material is too low, it is difficult to suppress lattice rotation in the cathode material. Preferably, 300ppm≤A1≤800ppm.

[0023] In some embodiments, the mass content of sulfur (A2) in the surface free sulfate ions of the cathode material satisfies 0 ppm < A2 ≤ 700 ppm. Specifically, it can be 50 ppm, 70 ppm, 100 ppm, 150 ppm, 500 ppm, 600 ppm, or 700 ppm, etc., or other values ​​within the above range, which are not limited here.

[0024] In some embodiments, the surface enrichment β of sulfur in the cathode material can specifically be 70%, 65%, 60%, 50%, 45%, 40%, 30%, 25%, 20%, or 10%, etc., and of course, other values ​​within the above range are also possible, without limitation. The presence of an appropriate amount of sulfur doping in the cathode material can improve the migration rate of lithium ions, suppress heterogeneous reactions, reduce lattice rotation of the cathode material, and enhance the structural stability of the cathode material. The higher the surface enrichment, the fewer sulfur atoms are doped into the crystal structure of the cathode material, and the lower the suppression effect on lattice rotation of the cathode material. Preferably, the surface enrichment β of sulfur in the cathode material is 40% ≤ β ≤ 50%.

[0025] In some embodiments, the general chemical formula of the cathode material is Li. x Ni a Co b N c M1 d O2, wherein 0.98≤x≤1.1, 0.5≤a≤0.98, 0<b≤0.2, 0<c≤0.30, 0≤d≤0.1, a+b+c+d=1, N element includes at least one of Mn and Al, and M1 element is a metallic element.

[0026] Specifically, the value of x can be 0.98, 0.99, 1.0, 1.02, 1.04, 1.05, 1.07, 1.08, 1.09, or 1.1, etc.; the value of a can be 0.5, 0.6, 0.7, 0.8, 0.82, 0.84, 0.85, 0.88, 0.89, 0.90, 0.92, 0.95, or 0.98, etc.; and the value of b can be 0.001, 0.01, 0.05, or 0. 1, 0.15, 0.16, 0.17, 0.19 or 0.2, etc.; c can be 0.001, 0.01, 0.05, 0.1, 0.15, 0.16, 0.18, 0.2, 0.25 or 0.3, etc.; d can be 0, 0.001, 0.005, 0.006, 0.008, 0.009, 0.01, 0.02, 0.03, 0.05, 0.07 or 0.1, etc., without limitation here.

[0027] In some embodiments, the M1 element includes at least one selected from Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn, and Y. Understandably, appropriate doping with the M1 element can improve the lattice structure stability of the cathode material and reduce lithium-nickel mixing.

[0028] In some embodiments, the percentage of particles smaller than 1 μm in the scanning electron microscope (SEM) image of the cathode material can be 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, or 18%, or other values ​​within the above range, without limitation. When the percentage of particles smaller than 1 μm is too high, it means an increase in the number of microparticles and a wider particle size distribution of the cathode material, which can improve the compaction density. However, an increase in the number of microparticles leads to an increase in the specific surface area of ​​the cathode material, causing more side reactions between the cathode material and the electrolyte, resulting in a decrease in the structural stability and cycle stability of the cathode material. When the percentage of particles smaller than 1 μm is too low, the lithium-ion transport path lengthens, the initial DCR of the cathode material increases, and the compaction density of the cathode material decreases. This application controls the proportion of particles with a diameter of less than 1 μm within the above-mentioned range, which can ensure that the compaction density of the cathode material is within a suitable range, improve the energy density of the cathode material, and at the same time help reduce the occurrence of side reactions between the cathode material and the electrolyte, thereby improving the structural stability and cycle stability of the cathode material.

[0029] In some embodiments, the cathode material comprises primary particles and a coating layer located on at least a portion of the surface of the primary particles. The coating layer comprises an oxide of element M2 and / or a lithium-ion conductor of element M2, wherein element M2 includes at least one selected from Al, Ti, Zr, Y, Nb, Mg, W, B, Ce, Co, and Mn. The presence of the coating layer on the surface of the primary particles can reduce side reactions between the primary particles and the electrolyte, and improve the structural stability of the primary particles.

[0030] In some embodiments, the cathode material is a single-crystal cathode material.

[0031] 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 if the color within a grain is the same, at least one grain has the same orientation, and 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 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.

[0032] Understandably, 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 particles" refer to the smallest particle unit identified when observing cathode active materials using a scanning electron microscope, while "secondary particles" refer to secondary particles 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 average particle size of a single particle in these quasi-secondary particles is between 1 μm and 5 μm. Generally, the roundness of quasi-secondary particles is lower than that of conventional polycrystalline "secondary particles."

[0033] 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 sense. In crystallography, an ideal single crystal is 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 a laboratory. Therefore, the single-crystal cathode materials known in the art are actually more accurately described as "single-crystal morphology" cathode materials, exhibiting only a large particle size similar to single crystals, distinguishing them from polycrystalline materials composed of numerous small primary particles.

[0034] In some embodiments, the median particle size of the cathode material is 1.5 μm to 5.0 μm, specifically 1.0 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, or 5.0 μm, etc., and of course, other values ​​within the above range are also possible, without limitation. Since most particles in the cathode material are primary particles, meaning the median particle size of the primary particles is within the above range, primary particles within this size range can effectively control the lithium-ion diffusion path, resulting in superior electrochemical performance, higher discharge capacity, and excellent rate performance.

[0035] In some implementations, the specific surface area of ​​the cathode material is 0.5 m². 2 / g~1.2m 2 / g; specifically, it can be 0.50m 2 / g, 0.55m 2 / g, 0.58m 2 / g, 0.6m 2 / g, 0.65m 2 / g, 0.7m 2 / g, 0.75m 2 / g, 0.8m 2 / g, 0.85m 2 / g, 0.9m 2 / g, 0.95m 2 / g, 1.0m 2 / g, 1.05m 2 / g, 1.1m 2 / g or 1.2m 2 / g, etc., can also be other values ​​within the above range, and are not limited here. Controlling the specific surface area of ​​the cathode material within the above range can effectively control the side reactions between the cathode material and the electrolyte, and improve the capacity of the cathode material.

[0036] In some embodiments, the compacted density of the cathode material powder is 3.0 g / cm³. 3 ~3.3g / cm 3 Specifically, it could be 3.0 g / cm³. 33.05g / cm 3 3.1g / cm 3 3.15g / cm 3 3.2g / cm 3 3.25g / cm 3 Or 3.3g / cm 3 Of course, other values ​​within the above range are also possible and are not limited here. Controlling the powder compaction density of the cathode material within the above range is beneficial to improving the specific capacity of the cathode material and the energy density of the battery made from the cathode material.

[0037] In some embodiments, during the first charge-discharge cycle, the structural recovery degree δ of the positive electrode material satisfies: 100.00% ≥ δ ≥ 99.70%; where δ = θ1 / θ2 * 100%, θ1 is the diffraction angle of the positive electrode material at the (003) crystal plane diffraction peak measured by X-ray diffraction at the beginning of the first charge cycle, and θ2 is the diffraction angle of the positive electrode material at the (003) crystal plane diffraction peak measured by X-ray diffraction at the end of the first discharge cycle.

[0038] Specifically, δ can be 99.7%, 99.8%, 99.85%, 99.9%, 99.95%, or 100.00%, or other values ​​within the above range, which are not limited here. Understandably, if the structural recovery degree of the cathode material is controlled within the above range, it is evident that the crystal structure of the cathode material can remain stable during charge-discharge cycles, the irreversible phase transition of the cathode material is reduced, and the lattice structure decay is significantly improved, which is beneficial to maintaining the cycle structure stability of the cathode material.

[0039] Secondly, this application provides a method for preparing the above-mentioned cathode material, comprising the following steps:

[0040] S10 involves preparing a mixed solution of nickel, cobalt, and a salt containing nitrogen in a specific stoichiometric ratio, adding an appropriate amount of dilute sulfuric acid solution, and atomizing the solution using a plasma rotating electrode to form microparticles with a particle size of 2 μm to 200 μm. These droplets are then passed into a calcining furnace for thermal decomposition to obtain an oxide precursor. The precursor contains 0.015% to 0.3% H2SO4, with a total molar content of 100% for the metallic Ni+Co+N. The nitrogen element includes at least one of Mn and Al.

[0041] S20, the mixture of oxide precursor and lithium source is subjected to a first sintering process, and the first sintering product is crushed to obtain the cathode material. The first sintering process includes a first heating stage, a second heating stage, a first cooling stage and a third heating stage in sequence. The temperature of the first heating stage is 300℃~600℃, the temperature of the second heating stage is 720℃~1000℃, the temperature of the first cooling stage is 500℃~700℃, and the temperature of the third heating stage is 720℃~1000℃.

[0042] The cathode material preparation method provided in this application involves adding an appropriate amount of dilute sulfuric acid during the preparation of the oxide precursor to achieve doping. The oxide precursor containing sulfate ions undergoes a single sintering process. During this single sintering process, some of the sulfate ions doped into the precursor can form an OT (Oxygen-Oxygen) reaction with metal elements and oxygen elements. M -S chemical bond, T M As a transition metal in the crystal lattice, this chemical bond has a stronger bond energy, which can enhance the cathode material's tolerance to lattice deformation, significantly alleviate the generation of internal cracks and irreversible phase transitions in cathode material particles, and improve the cycle stability of the cathode material.

[0043] The preparation method of this application is described in detail below with reference to the embodiments:

[0044] Step S10: Prepare a mixed solution of nickel, cobalt and a salt containing nitrogen element according to a certain stoichiometric ratio, add an appropriate amount of dilute sulfuric acid solution, and atomize it through a plasma rotating electrode to form microparticle droplets with a particle size of 2μm to 200μm. Then, pass the droplets into a calcination furnace for thermal decomposition to prepare the oxide precursor.

[0045] In some implementations, the stoichiometric ratios of nickel, cobalt, and nitrogen meet the following conditions: 0.5 ≤ Ni < 1, 0 < Co ≤ 0.2, 0 < N ≤ 0.35; the molar ratio of Ni:Co:N can specifically be 0.60:0.05:0.35, 0.67:0.05:0.28, 0.90:0.5:0.05, or 0.98:0.01:0.01, etc.

[0046] In some embodiments, the salt solution is at least one of nitrate, hydrochloride, carbonate, oxalate, and acetate. For example, the nickel salt solution may be at least one of nickel chloride, nickel nitrate, nickel carbonate, nickel oxalate, and nickel acetate. Of course, nickel, manganese, and nitrogen elements may also be recycled materials from ternary cathode materials, and this is not limited thereto.

[0047] In some embodiments, with the total molar content of metals Ni, Co, and N being 100%, the amount of H2SO4 added is 0.015% to 0.3%. Specifically, the amount of H2SO4 added can be 0.015%, 0.03%, 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.2%, 0.25%, 0.3%, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0048] In some embodiments, the calcination furnace includes a first temperature zone, a second temperature zone, and a third temperature zone. The temperature in the first temperature zone is 300℃ to 500℃, during which the droplets rapidly dehydrate. The temperature in the second temperature zone is 1000℃ to 1200℃, and the material residence time is 2s to 10s. This brief high temperature can promote the doping of sulfur into the precursor and effectively prevent the precursor particles from growing too large, thus affecting the reactivity of the precursor. The third temperature zone is 500℃ to 800℃, where the material undergoes pyrolysis, and various metal salts decompose to form oxide precursor particles.

[0049] In some implementations, the oxygen volume concentration in the roasting furnace is controlled to be ≤21%.

[0050] In some embodiments, the temperature of the first temperature zone can be 300°C, 350°C, 380°C, 400°C, 430°C, 450°C, or 500°C, or other values ​​within the above range, which are not limited here. The residence time in the first temperature zone is 1 min to 5 min, specifically 1 min, 2 min, 3 min, 4 min, or 5 min, or other values ​​within the above range.

[0051] In some embodiments, the temperature of the second temperature can be 1000℃, 1050℃, 1100℃, 1150℃, or 1200℃, or other values ​​within the above range, which are not limited here. The residence time in the second temperature zone is 2s to 10s, specifically 2s, 3s, 5s, or 10s, or other values ​​within the above range.

[0052] In some embodiments, the temperature of the third temperature zone can be 510℃, 520℃, 530℃, 550℃, 600℃, 650℃, 680℃, 700℃, 750℃, or 800℃, or other values ​​within the above range, which are not limited here. The residence time in the third temperature zone is 3min to 8min, specifically 3min, 4min, 5min, 6min, or 8min, or other values ​​within the above range.

[0053] In some embodiments, the calcined product is subjected to air jet milling to control the D50 of the oxide precursor to be 2.5 μm to 4.5 μm and Dmax < 20 μm. Specifically, D50 can be 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.2 μm, or 4.5 μm, or other values ​​within the above range.

[0054] This application utilizes airflow pulverization of the calcined product to control the particle size distribution of the precursor, which is beneficial for controlling the proportion of excessively small particles and the electrochemical performance of the cathode material.

[0055] In some embodiments, a compound containing element M1 is also added to the mixed solution according to the target doping ratio. Specifically, it may be a nitrate containing element M1, a hydrochloride containing element M1, an acid containing element M1, etc., which is not limited here.

[0056] In some embodiments, the M1 element includes at least one selected from Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn, and Y.

[0057] In some embodiments, the general chemical formula of the oxide precursor is Ni. x Co y N z M1 d O e Wherein, 0.50≤x≤0.98, 0<y≤0.20, 0<z≤0.35, 0≤d≤0.1, x+y+z+d=1; 1≤e≤1.5. Wherein, N is either Mn or Al.

[0058] S20 involves sintering a mixture of oxide precursor and lithium source in one pass, and then crushing the sintered product to obtain the cathode material.

[0059] In some embodiments, the lithium source includes at least one selected from lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium sulfate, and lithium oxalate. Preferably, the lithium salt is lithium carbonate.

[0060] In some embodiments, the addition amounts of the lithium source and oxide precursor satisfy the following: the molar ratio of Li to the total molar amount of all metals in the oxide precursor is (0.98–1.1):1, specifically 0.98:1, 1.02:1, 1.05:1, 1.1:1, etc., or other values ​​within the above range, which are not limited here. Within this range, the Li / Ni cation mixing degree can be reduced, and excessive residual lithium on the surface of the calcined product can be prevented from affecting processing performance and safety performance.

[0061] In some embodiments, the mixing conditions for obtaining the mixture are: solid-phase mixing at 10°C to 50°C for 0.3h to 3h.

[0062] In some embodiments, the solid-phase mixing temperature can be 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, or 50°C, and the solid-phase mixing time can be 0.3h, 0.4h, 0.5h, 0.6h, 0.8h, 1h, 1.5h, 1.8h, 2.5h, or 3h, etc. Of course, other values ​​within the above ranges are also possible and are not limited here.

[0063] In some implementations, the mixing equipment may be at least one of a ball mill, a three-dimensional mixer, a high-speed mixer, and a VC mixer.

[0064] In some embodiments, the primary sintering process includes sequentially performing a first heating stage, a second heating stage, a first cooling stage, and a third heating stage. The temperature of the first heating stage is 300℃ to 600℃, the temperature of the second heating stage is 720℃ to 1000℃, the temperature of the first cooling stage is 500℃ to 700℃, and the temperature of the third heating stage is 720℃ to 1000℃.

[0065] In some embodiments, the temperature of the first heating stage can be 300°C, 350°C, 380°C, 400°C, 430°C, 450°C, 500°C, 550°C, 580°C, or 600°C, etc. The duration of the first heating stage is 3h to 5h, specifically 3h, 3.5h, 4h, 4.5h, or 5h, but not limited to the listed values; other unlisted values ​​within this range are also applicable. The temperature of the first heating stage is relatively low, at which time the lithium source can fully melt and react with the oxide precursor.

[0066] In some embodiments, the heating rate of the first heating stage is 15℃ / min to 20℃ / min, specifically 15℃ / min, 16℃ / min, 17℃ / min, 18℃ / min, 19℃ / min or 20℃ / min, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0067] In some embodiments, the temperature of the second heating stage can be 720°C, 770°C, 800°C, 880°C, 900°C, or 1000°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The duration of the second heating stage is 4h to 12h, specifically 4h, 5h, 6h, 8h, 9h, 10h, 11h, or 12h, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. During the second heating stage, the crystals of the cathode material grow sufficiently.

[0068] In some embodiments, the heating rate of the second heating stage is 0.5℃ / min to 3℃ / min, specifically 0.5℃ / min, 0.6℃ / min, 0.7℃ / min, 1.0℃ / min, 1.2℃ / min, 1.5℃ / min, 2.0℃ / min, 2.2℃ / min, 2.5℃ / min, 2.8℃ / min or 3℃ / min, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0069] In some embodiments, the temperature of the first cooling stage can be 500℃, 550℃, 580℃, 600℃, 620℃, 650℃, 680℃, 690℃, or 700℃, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The duration of the first cooling stage is 2h to 6h, specifically 2h, 3h, 4h, 5h, 5.5h, or 6h, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Cooling treatment can release the lattice stress of the cathode material and improve the stability of the crystal.

[0070] In some embodiments, the cooling rate of the first cooling stage is 0.5℃ / min to 3℃ / min, specifically 0.5℃ / min, 0.6℃ / min, 0.7℃ / min, 1.0℃ / min, 1.2℃ / min, 1.5℃ / min, 2.0℃ / min, 2.2℃ / min, 2.5℃ / min, 2.8℃ / min or 3℃ / min, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0071] In some embodiments, the temperature of the third heating stage can be 720°C, 770°C, 800°C, 880°C, 900°C, or 1000°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The duration of the third heating stage is 1 hour to 3 hours, specifically 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. During the third heating stage, the crystals of the cathode material are fully grown.

[0072] In some embodiments, the heating rate of the third heating stage is 0.5℃ / min to 3℃ / min, specifically 0.5℃ / min, 0.6℃ / min, 0.7℃ / min, 1.0℃ / min, 1.2℃ / min, 1.5℃ / min, 2.0℃ / min, 2.2℃ / min, 2.5℃ / min, 2.8℃ / min or 3℃ / min, etc. Of course, other values ​​within the above range are also possible and are not limited here.

[0073] In some embodiments, the sintered product is cooled to room temperature after the third heating stage.

[0074] In some embodiments, the primary sintering process is carried out in an oxygen-containing atmosphere with an oxygen content ≥95%.

[0075] In this application, the temperature of each stage in the sintering process is adjusted according to the molar content in the oxide precursor. The higher the Ni content, the lower the sintering temperature, which can effectively improve the lithium-nickel mixing phenomenon.

[0076] In some embodiments, the method further includes: mixing the crushed product with a coating agent containing metal M2, and then performing a secondary sintering treatment to obtain a cathode material.

[0077] In some embodiments, the crushing method includes at least one of a double roller mill, a plow-type agitator / crusher, and an air jet mill.

[0078] In some embodiments, the coating agent containing metal M2 is selected from at least one of Al, Ti, Zr, Y, Nb, Mg, W, B, Ce, Co, and Mn. The coating agent containing metal M2 can be a salt or oxide of metal M. Preferably, the coating agent containing metal M2 includes compounds of Nb and / or compounds of W.

[0079] In some embodiments, the secondary sintering process is carried out in an oxygen-containing atmosphere with an oxygen content ≥95%.

[0080] In some embodiments, the temperature of the secondary sintering treatment is 300℃ to 800℃, specifically 300℃, 320℃, 330℃, 350℃, 380℃, 400℃, 450℃, 500℃, 550℃, 650℃, 700℃ or 800℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0081] In some embodiments, the holding time for the secondary sintering treatment is 6h to 24h, specifically 6h, 8h, 10h, 12h, 15h, 18h or 24h, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0082] Thirdly, this application provides a battery comprising the positive electrode material described in the first aspect or a positive electrode material prepared according to the method for preparing the positive electrode material described above.

[0083] The battery provided in this application can be a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, electrode assembly, and electrolyte. Both the electrode assembly and electrolyte are located inside the casing. The casing can be a packaging bag sealed with an encapsulating film (such as an aluminum-plastic film), such as a pouch battery for secondary batteries.

[0084] In other embodiments, the secondary battery may also be a steel-cased battery, an aluminum-cased battery, etc.

[0085] Figure 1 is a schematic diagram of the discharge state of the battery provided in an embodiment of this application. As shown in Figure 1, the battery includes a casing and an electrode assembly. The electrode assembly includes a positive electrode 1, a negative electrode 2, and a separator 3, with the separator 3 disposed between the positive electrode 1 and the negative electrode 2. The electrode assembly can be a stacked structure, which is formed by alternating layers of the positive electrode 1, the separator 3, and the negative electrode 2.

[0086] In other embodiments, the electrode assembly can also be a wound structure, which is formed by sequentially stacking and winding a positive electrode, a separator, and a negative electrode.

[0087] In some embodiments, the positive electrode 1 includes a positive current collector 11 and a positive active material layer 12 disposed on at least one surface of the positive current collector 11.

[0088] In some embodiments, the positive electrode current collector 11 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 (aluminum foil or nickel foil, etc.) and the polymer substrate. The positive electrode active material layer 12 comprises a positive electrode active material, a conductive agent, and a binder, wherein the positive electrode active material is the positive electrode material of the first aspect described above or a positive electrode material prepared according to the above-described method for preparing the positive electrode material.

[0089] In some embodiments, the positive electrode 1 is prepared by mixing positive active material, conductive agent, binder and solvent in a certain proportion to form a slurry, then uniformly coating the slurry onto the positive current collector 11, and drying it under vacuum at a certain temperature to obtain the positive electrode 1.

[0090] In some embodiments, the conductive agent includes at least one of conductive carbon black, graphene, carbon nanofibers, Ketjen black, graphite, acetylene black, and MXene.

[0091] In some embodiments, the binder includes at least one of sodium carboxymethyl cellulose, cyclodextrin, styrene rubber latex, polyacrylate, and polyvinylidene fluoride.

[0092] In some embodiments, the solvent is selected from at least one of deionized water, N-methylpyrrolidone, and N,N-dimethylformamide.

[0093] In some embodiments, the vacuum drying temperature is 60°C to 120°C, specifically 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, or 120°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Preferably, the vacuum drying temperature is 110°C.

[0094] In some embodiments, the negative electrode 2 includes a negative electrode current collector 21 and a negative electrode active material layer 22 disposed on at least one surface of the negative electrode current collector.

[0095] In some embodiments, the negative electrode current collector 21 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 electrode active material layer 22 includes a negative electrode material, which includes, but is not limited to, at least one of natural graphite negative electrode material, natural graphite negative electrode material, or silicon-based negative electrode material.

[0096] The embodiments of the present invention will be further described below with reference to several examples. However, the embodiments of the present invention are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the original claims.

[0097] Test method:

[0098] (1) Test of free sulfate ions in positive electrode materials

[0099] Weigh 0.5 g of sample and disperse it in 50 ml of pure water. After sonication for 5 min, filter the solution and measure the free SO4 in the filtrate using an ion chromatograph (instrument: Thermo Fisher ICS6000 HPIC). 2- The mass content of the ions is a2.

[0100] Since sulfur accounts for 1 / 3 of the mass of sulfate, the mass content of sulfur in the free sulfate of the cathode material is A2 = a2 / 3.

[0101] (2) Test of total mass content of sulfur in cathode material

[0102] Take 0.3g of sample, add aqua regia to digest, cool and make up to a volume of 100ml of mother liquor, and test the mother liquor by inductively coupled plasma optical emission spectrometry (Agilent 5110ICP-OES) to obtain the total mass content of S element A1.

[0103] The surface enrichment degree of sulfur is β = A2 / A1. The ratio of A1 to A2 can characterize the degree of sulfur enrichment on the surface of the cathode material. The larger the ratio of A1 to A2, the higher the sulfur content on the surface of the cathode material, and the more sulfur is enriched on the surface of the cathode material. The smaller the ratio of A1 to A2, the lower the sulfur content on the surface of the cathode material, and the higher the sulfur content in the bulk phase.

[0104] (3) The proportion of particles with a diameter of less than 1 μm in the cathode material

[0105] 1) Use a cotton swab to pick up a small amount of powder sample and spread it evenly and densely on the conductive adhesive; use a hair dryer to slowly blow it in the direction where there are no other samples, and when you are sure that it is evenly spread on the surface, blow it strongly more than 10 times until there is no powder residue.

[0106] 2) Set the basic SEM conditions: voltage 5kV, current 12mA, magnification 2kx, and adjust contrast and brightness using the auto key; randomly select 10 areas with 300 to 800 particles to take electron microscope images;

[0107] 3) Import the electron microscope image obtained in step (2) into the Metis Vision software, click "Identify All" in the software interface to obtain the particle size distribution data and particle size distribution map in the electron microscope image, thereby obtaining the proportion of particles with a particle size of less than 1 μm.

[0108] (4) IPC test method for elemental content in cathode materials:

[0109] Equipment: Agilent 5110ICP-OES Plasma Inductive Coupling System.

[0110] Method: Take 0.3g of sample, add aqua regia to digest, cool and make up to 100ml of mother liquor. Take 1mL of the mother liquor, dilute it 100 times and test the content of the main elements Li / Ni / Co / Mn / Al. Test the content of impurity elements in the mother liquor.

[0111] (5) XRD testing methods for cathode materials:

[0112] Equipment: X'Pert Powder or Bruker X-ray diffraction analyzer.

[0113] Methods: Electrochemical in-situ XRD was used to characterize the changes in the (003) and (104) peaks during the charge and discharge process of the cathode material. The cathode materials prepared in the above examples and comparative examples were assembled to form mold batteries. The outer shell of the mold battery was a Bruker in-situ XRD device or an X'Pert Powder in-situ XRD device, and the outer shell had a window that allowed X-rays from the XRD device to pass through. The specific procedure is as follows: The cathode material, conductive carbon black, and PVDF were weighed in a mass ratio of 93:5:2. N-methyl-2-pyrrolidone (NMP) was added at a solid content of 50%. The mixture was dispersed into a viscous slurry using a high-speed disperser. The slurry was uniformly coated onto aluminum foil using a 200-micron scraper. After baking in an oven at 80°C for 30 minutes, the mixture was rolled and punched into a cathode sheet with a diameter of 14 mm. The sheet was then placed back into the oven and baked at 80°C for 8 hours. Using a prepared positive electrode, a 16mm lithium sheet as the negative electrode, a Celgard polypropylene membrane as the separator, and a 1mol / L LiPF6 carbonate solution as the electrolyte, the mold battery was assembled in an argon-filled glove box using the casing of the XRD equipment. The mold battery was then subjected to charge-discharge tests at 25℃ and 2.5V-4.35V, and the changes in the (003) and (104) peaks of the positive electrode material within one cycle were characterized by in-situ electrochemical XRD. The structural recovery degree of the positive electrode material was δ = θ1 / θ2 * 100%, where θ1 is the diffraction angle of the positive electrode material at the (003) crystal plane diffraction peak measured by X-ray diffraction at the beginning of the first charge cycle, and θ2 is the diffraction angle of the positive electrode material at the (003) crystal plane diffraction peak measured by X-ray diffraction at the end of the first discharge cycle.

[0114] (6) Test method for particle size of cathode material:

[0115] The volumetric cumulative particle size distribution of the cathode material was measured using a Malvern laser particle size analyzer (Mastersizer 3000 laser particle size analyzer) to obtain D. 90 D 50 and D 10 Specifically, take an appropriate amount of sample, pour it into pure water, and ultrasonically disperse it for 30 seconds at a power of 240W. Then, add an appropriate amount of sodium hexametaphosphate to the dispersed sample, stir well, and pour it into the sample cell of the testing equipment. After waiting 10 seconds, click "Start" to begin the sample test. D10 represents the particle size corresponding to a cumulative particle size distribution percentage of 10%, D50 represents the particle size corresponding to a cumulative particle size distribution percentage of 50%, and D90 represents the particle size corresponding to a cumulative particle size distribution percentage of 90%.

[0116] (7) Test method for specific surface area of ​​cathode material:

[0117] Equipment: The specific surface area of ​​the cathode material was tested using a Microt Tristar 3020 specific surface area and pore size analyzer.

[0118] Method: Weigh the empty sample tube (m1); add 3g of sample into the sample tube through a long-necked funnel; degas under vacuum at 300℃ for 1h, cool, and weigh the sample tube (m2); the sample mass is m = m2 - m1. Place the sample tube in liquid nitrogen and measure the nitrogen adsorption capacity V of the sample under a series of relative pressures P / P0 to obtain adsorption isotherms. P / P0 is set to 0.05 / 0.1 / 0.15 / 0.20 / 0.25 / 0.30. Fit the isothermal adsorption curve, calculate the monolayer saturated adsorption capacity Vm based on the slope and intercept, and then calculate the specific surface area based on Vm.

[0119] (8) Cathode material compaction density test:

[0120] The compaction density of the cathode material was tested using a Carver 4350 from the United States. The procedure was as follows: 1g of sample was placed in a mold and pressed with a pressure of 3T for 30s. After pressing, the height was measured and the compaction was calculated.

[0121] (9) Average particle size test of primary particles of cathode material:

[0122] Equipment: Hitachi S4800 scanning electron microscope and energy scattering spectroscopy instrument from OXFORD Instruments.

[0123] Methods: Five random images of samples at different locations were taken using a Hitachi S4800 scanning electron microscope at 3000x magnification. The maximum diameter of the single-crystal particles completely visible in the electron microscope image was measured using Nano Measure software. The average diameter of the particles was calculated as the average particle size. A single-crystal particle completely visible in the electron microscope image is defined as one whose outline is fully displayed in the image, without being obscured by other single-crystal particles or divided by the boundaries of the image. The maximum diameter of a single-crystal particle refers to the diameter of its circumcircle in the electron microscope image.

[0124] (10) Electrochemical performance testing:

[0125] The positive electrode material, conductive carbon black, and PVDF (polyvinylidene fluoride) binder were mixed in a mass ratio of 80:10:10. NMP (N-methylpyrrolidone) was then added to form a uniform slurry. This slurry was evenly coated onto aluminum foil and dried in a 100℃ oven for 12 hours. After drying, it was rolled under 10 MPa pressure and cut into circular electrode sheets with a diameter of 14 mm. The negative electrode used a 14 mm diameter Li metal sheet. The lithium-ion battery was assembled according to the industrial CR2025 button cell design. A Cellgard separator was used, and the electrolyte was a mixture of equal parts ethylene carbonate (EC), polycarbonate (PC), and diethyl carbonate (DEC) with 1 mol / L LiPF6 as the electrolyte. The positive electrode sheet, separator, negative electrode sheet, and electrolyte were assembled into a button cell in an Ar gas glove box with a water and oxygen content of less than 0.5 ppm.

[0126] Capacity testing: The electrical performance was tested using the Blue Electric testing system (charge and discharge voltage of 3.0 to 4.3V, temperature condition of 25℃), with 0.1C charging, 0.1C discharging, and a constant voltage cutoff current of 0.005C. The discharge specific capacity mAh / g was calculated.

[0127] Cyclic test: At 25℃ and under a charge / discharge voltage of 3.0~4.3V, the system is charged and discharged at 0.5C / 1C for 50 cycles. The final capacity retention rate after 50 cycles is the cycle performance.

[0128] DC internal resistance (DCR) test: Charge at 0.1C and discharge at 0.1C to 3.7V. After standing for 5 hours, place the battery at 25℃ and then discharge at 2C for 30 seconds. Take a point every 0.1 seconds and calculate the average internal resistance over 30 seconds as DCR (DC internal resistance).

[0129] Example 1

[0130] (1) Weigh nickel nitrate, cobalt nitrate and manganese nitrate into water and add them to prepare a metal salt mixed solution by adding 0.12% of H2SO4 relative to the total molar amount of Ni / Co / Mn metals into the mixed solution. Stir the solution with ultrasonic for 2 hours to ensure thorough mixing and obtain a mixed solution.

[0131] (2) The mixed solution was atomized using a plasma rotating electrode to form microparticles approximately 20 μm in size. These droplets were then passed into a calcining furnace for thermal decomposition to prepare the oxide precursor. The temperature in the first zone was 400℃, with a residence time of 60 s; the temperature in the second zone was 1100℃, with a residence time of 5 s; and the temperature in the third zone was 700℃, with a residence time of 3 min. The oxygen volume concentration in the calcining furnace was controlled at 15%. The chemical formula of the oxide precursor is Ni. 0.60 Co 0.1 Mn0.3 O 1.25 The precursor is pulverized by airflow to a suitable particle size D50 = 3.0 μm and Dmax = 15.

[0132] (3) The oxide precursor and Li2CO3 were mixed at a molar ratio of Li / Me (Me is the sum of Ni, Co and Mn) of 1.05:1 and placed in a Joule thermal reactor. An oxygen atmosphere was used and the reaction pressure was controlled at 10 Pa. The temperature was increased from room temperature to the first stage temperature of 500℃ at a heating rate of 20℃ / min and held for 4 h. The temperature was increased to the second stage temperature of 700℃ at a heating rate of 2℃ / min and held for 6 h. The temperature was decreased to the third stage temperature of 500℃ at a cooling rate of 1℃ / min and held for 4 h. The temperature was increased to the fourth stage temperature of 900℃ at a heating rate of 1℃ / min and held for 2 h. The temperature was decreased from the fourth stage temperature to room temperature at a cooling rate of 2℃ / min and the cathode material was obtained by air jet pulverization.

[0133] Example 2

[0134] The difference from Example 1 is:

[0135] In step (1), the amount of H2SO4 added to the solution was reduced to 0.015%.

[0136] Example 3

[0137] Unlike Example 1,

[0138] In step (1), the amount of H2SO4 added to the solution is increased to 0.30%.

[0139] Example 4

[0140] Unlike Example 1,

[0141] In step (2), the volume concentration of oxygen is controlled at 21%.

[0142] Example 5

[0143] The difference from Example 1 is:

[0144] In step (3), the specific steps of the first sintering process are as follows: using an oxygen atmosphere, the reaction pressure is controlled at 2Pa; heating from room temperature to the first stage temperature of 600℃ at a heating rate of 20℃ / min, and holding for 5h; heating from the second stage temperature of 1000℃ at a heating rate of 0.5℃ / min, and holding for 12h; cooling down to the third stage temperature of 700℃ at a cooling rate of 0.5℃ / min, and holding for 6h; heating up to the fourth stage temperature of 1000℃ at a heating rate of 0.5℃ / min, and holding for 3h; cooling down from the fourth stage temperature to room temperature at a cooling rate of 1℃ / min, and obtaining the positive electrode material through airflow pulverization.

[0145] Example 6

[0146] Unlike Example 1:

[0147] In step (3), the specific steps of the first sintering process are as follows: using an oxygen atmosphere, the reaction pressure is controlled at 10 Pa; heating from room temperature to the first stage temperature of 300℃ at a heating rate of 20℃ / min, and holding for 5 hours; heating to the second stage temperature of 900℃ at a heating rate of 3℃ / min, and holding for 4 hours; cooling down to the third stage temperature of 600℃ at a cooling rate of 3℃ / min, and holding for 6 hours; heating up to the fourth stage temperature of 700℃ at a heating rate of 3℃ / min, and holding for 6 hours; cooling down from the fourth stage temperature to room temperature at a cooling rate of 1℃ / min, and obtaining the positive electrode material through airflow pulverization.

[0148] Example 7

[0149] (1) Weigh nickel nitrate, cobalt nitrate and manganese nitrate into water and add them to prepare a metal salt mixed solution by adding 0.12% of H2SO4 relative to the total molar of Ni / Co / Mn metals into the mixed solution. Stir the solution with ultrasonic for 2 hours to ensure thorough mixing and obtain a mixed solution.

[0150] (2) The mixed solution was atomized using a plasma rotating electrode to form microparticles approximately 20 μm in size, which were then fed into a calcining furnace for thermal decomposition to prepare the oxide precursor. The first temperature zone was 400℃ with a residence time of 60 s; the second temperature zone was 1100℃ with a residence time of 3 s; and the third temperature zone was 700℃ with a residence time of 3 min. The oxygen volume concentration in the calcining furnace was controlled at 15%. The chemical formula of the oxide precursor is Ni. 0.5 Co 0.2 Mn 0.3 O 1.2 The oxide precursor is pulverized by airflow to a suitable particle size D50 = 3.0 μm and Dmax = 15.

[0151] (3) The oxide precursor and Li2CO3 were mixed at a molar ratio of Li / Me (Me is the sum of Ni, Co and Mn) of 1.05:1 and placed in a Joule thermal reactor. An oxygen atmosphere was used and the reaction pressure was controlled at 10 Pa. The temperature was increased from room temperature to the first stage temperature of 500℃ at a heating rate of 20℃ / min and held for 4 h. The temperature was increased to the second stage temperature of 800℃ at a heating rate of 2℃ / min and held for 6 h. The temperature was decreased to the third stage temperature of 500℃ at a cooling rate of 1℃ / min and held for 4 h. The temperature was increased to the fourth stage temperature of 1000℃ at a heating rate of 1℃ / min and held for 2 h. The temperature was decreased from the fourth stage temperature to room temperature at a cooling rate of 2℃ / min and the cathode material was obtained by air jet pulverization.

[0152] Example 8

[0153] (1) Weigh nickel nitrate, cobalt nitrate and manganese nitrate in water at a molar ratio of nNi:nCo=0.98:0.01:0.01 to prepare a mixed solution of metal salts. Then add 0.12% H2SO4 to the mixed solution and stir ultrasonically for 2 hours to ensure thorough mixing and obtain a mixed solution.

[0154] (2) The mixed solution was atomized using a plasma rotating electrode to form microparticles approximately 20 μm in size, which were then fed into a calcining furnace for thermal decomposition to prepare the oxide precursor. The first temperature zone was 400℃ with a residence time of 60 s; the second temperature zone was 1100℃ with a residence time of 5 s; and the third temperature zone was 700℃ with a residence time of 3 min. The oxygen volume concentration in the calcining furnace was controlled at 15%. The chemical formula of the oxide precursor is Ni. 0.98 Co 0.01 Mn 0.01 O, the oxide precursor is pulverized by airflow to a suitable particle size D50 = 3.0 μm, Dmax = 15.

[0155] (3) The oxide precursor and Li2CO3 are mixed at a molar ratio of Li / Me (Me is the sum of Ni, Co and Mn) of 0.98:1 and placed in an atmosphere electric furnace or Joule thermal reactor. An oxygen atmosphere is used and the reaction pressure is controlled at 10 Pa. The temperature is increased from room temperature to the first stage temperature of 500℃ at a heating rate of 20℃ / min and held for 4 hours. The temperature is increased to the second stage temperature of 700℃ at a heating rate of 2℃ / min and held for 6 hours. The temperature is decreased to the third stage temperature of 500℃ at a cooling rate of 1℃ / min and held for 4 hours. The temperature is increased to the fourth stage temperature of 700℃ at a heating rate of 1℃ / min and held for 2 hours. The temperature is decreased from the fourth stage temperature to room temperature at a cooling rate of 2℃ / min and the cathode material is obtained by air jet pulverization.

[0156] Example 9

[0157] (1) Weigh nickel nitrate, cobalt nitrate and manganese nitrate into water and add them to prepare a metal salt mixed solution. Then add 0.12% of H2SO4 relative to the total molar of Ni / Co / Mn metals to the mixed solution and stir ultrasonically for 2 hours to make it fully mixed and homogeneous to obtain a mixed solution.

[0158] (2) The mixed solution was atomized using a plasma rotating electrode to form microparticles approximately 20 μm in size, which were then fed into a calcining furnace for thermal decomposition to prepare the oxide precursor. The first temperature zone was 400℃ with a residence time of 60 s; the second temperature zone was 1100℃ with a residence time of 3 s; and the third temperature zone was 700℃ with a residence time of 3 min. The oxygen volume concentration in the calcining furnace was controlled at 15%. The chemical formula of the oxide precursor is Ni. 0.8 Co 0.1 Mn 0.1 O 1.1 The oxide precursor is pulverized by airflow to a suitable particle size D50 = 3.0 μm and Dmax = 15.

[0159] (3) The oxide precursor and LiOH are mixed at a molar ratio of Li / Me (Me is the sum of Ni, Co and Mn) of 1.1:1 and placed in an atmosphere electric furnace or Joule thermal reactor. An oxygen atmosphere is used and the reaction pressure is controlled at 10 Pa. The temperature is increased from room temperature to the first stage temperature of 500℃ at a heating rate of 20℃ / min and held for 4 hours. The temperature is increased to the second stage temperature of 750℃ at a heating rate of 2℃ / min and held for 6 hours. The temperature is decreased to the third stage temperature of 550℃ at a cooling rate of 1℃ / min and held for 4 hours. The temperature is increased to the fourth stage temperature of 850℃ at a heating rate of 1℃ / min and held for 2 hours. The temperature is decreased from the fourth stage temperature to room temperature at a cooling rate of 2℃ / min and the cathode material is obtained by air jet pulverization.

[0160] Example 10

[0161] (1) Weigh nickel nitrate, cobalt nitrate and manganese nitrate into water at a molar ratio nNi:nCo=0.70:0.10:0.20 to prepare a metal salt mixed solution. Then add 0.12% H2SO4 relative to the total molar of Ni / Co / Mn metals to the mixed solution and sonicate for 2 hours to ensure thorough mixing and obtain a mixed solution.

[0162] (2) The mixed solution was atomized using a plasma rotating electrode to form microparticles approximately 20 μm in size, which were then fed into a calcining furnace for thermal decomposition to prepare the oxide precursor. The first temperature zone was 400℃ with a residence time of 60 s; the second temperature zone was 1100℃ with a residence time of 3 s; and the third temperature zone was 700℃ with a residence time of 3 min. The oxygen volume concentration in the calcining furnace was controlled at 15%. The chemical formula of the oxide precursor is Ni. 0.7 Co 0.1 Mn 0.2 O, the oxide precursor is pulverized by airflow to a suitable particle size D50 = 3.0 μm, Dmax = 15.

[0163] (3) The oxide precursor and Li2CO3 are mixed at a molar ratio of Li / Me (Me is the sum of Ni, Co and Mn) of 0.98:1 and placed in an atmosphere electric furnace or Joule thermal reactor. An oxygen atmosphere is used and the reaction pressure is controlled at 10 Pa. The temperature is increased from room temperature to the first stage temperature of 500℃ at a heating rate of 20℃ / min and held for 4 hours. The temperature is increased to the second stage temperature of 700℃ at a heating rate of 2℃ / min and held for 6 hours. The temperature is decreased to the third stage temperature of 500℃ at a cooling rate of 1℃ / min and held for 4 hours. The temperature is increased to the fourth stage temperature of 880℃ at a heating rate of 1℃ / min and held for 2 hours. The temperature is decreased from the fourth stage temperature to room temperature at a cooling rate of 2℃ / min and the cathode material is obtained by air jet pulverization.

[0164] Example 11

[0165] The difference from Example 1 is:

[0166] (1) Weigh out nickel nitrate, cobalt nitrate, manganese nitrate and zirconium nitrate in water at a molar ratio of nNi:nCo:nMn:nZr = 0.6:0.1:0.3:0.005 to prepare a mixed solution of metal salts. Then add 0.12wt% H2SO4 relative to the total molar of Ni / Co / Mn / Zr metals to the mixed solution and stir ultrasonically for 2 hours to ensure thorough mixing and obtain a mixed solution.

[0167] The other steps are the same as in Example 1.

[0168] Example 12

[0169] The difference from Example 1 is:

[0170] The air jet milling product prepared in step (3) was mixed with alumina at a mass ratio of 99:1 and placed in a Joule thermal reactor. Using an air atmosphere, the temperature was increased from room temperature to 450°C at a heating rate of 20°C / min and held for 8 hours. Then, the temperature was reduced to room temperature at a rate of 2°C / min to obtain the cathode material.

[0171] Example 13

[0172] The difference from Example 9 is:

[0173] In step (1), nickel nitrate, cobalt nitrate, and aluminum nitrate were weighed and added to water in a molar ratio of nNi:nCo:nAl = 0.8:0.1:0.1 to prepare a metal salt mixed solution. Then, 0.12% of H2SO4 relative to the total molar of Ni / Co / Al metals was added to the mixed solution, and the solution was ultrasonically stirred for 2 hours to ensure thorough mixing and obtain a mixed solution.

[0174] In step (3), the temperature of the fourth stage is set to 870℃.

[0175] Example 14

[0176] Unlike Example 1,

[0177] (1) Weigh nickel nitrate, cobalt nitrate and manganese nitrate into water and add them to prepare a metal salt mixed solution by molar ratio nNi:nCo:nMn=0.6:0.1:0.3. Then add 0.6% H2SO4 to the mixed solution and stir ultrasonically for 2 hours to make it fully mixed and homogeneous to obtain a mixed solution.

[0178] Comparative Example 1

[0179] Unlike Example 1,

[0180] (2) The mixed solution was atomized using a plasma rotating electrode to form microparticles approximately 20 μm in size, which were then thermally decomposed in a calcination furnace to prepare the oxide precursor. The first temperature zone was 400℃ with a residence time of 60 s; the second temperature zone was 700℃ with a residence time of 3 min. The oxygen volume concentration in the calcination furnace was controlled at 15%. The chemical formula of the oxide precursor is Ni. 0.60 Co 0.1 Mn 0.3 O, the precursor is pulverized by airflow to a suitable particle size D50 = 3.0 μm, Dmax = 15.

[0181] Comparative Example 2

[0182] Unlike Example 1,

[0183] (2) The mixed solution was atomized using a plasma rotating electrode to form microparticles approximately 20 μm in size, which were then fed into a calcining furnace for thermal decomposition to prepare the oxide precursor. The first temperature zone was 400℃ with a residence time of 60 s; the second temperature zone was 1100℃ with a residence time of 3 s; and the third temperature zone was 700℃ with a residence time of 3 min. The oxygen volume concentration in the calcining furnace was controlled at 30%. The chemical formula of the oxide precursor is Ni.0.60 Co 0.1 Mn 0.3 O, the oxide precursor is pulverized by airflow to a suitable particle size D50 = 3.0 μm, Dmax = 15.

[0184] Comparative Example 3

[0185] Unlike Example 1,

[0186] (3) The oxide precursor and Li2CO3 are mixed at a molar ratio of Li / Me (Me is the sum of Ni, Co and Mn) of 1.05:1 and placed in an atmosphere electric furnace or Joule thermal reactor. An oxygen atmosphere is used and the reaction pressure is controlled at 2 Pa. The temperature is increased from room temperature to the first stage temperature of 600℃ at a heating rate of 20℃ / min and held for 5 h. The temperature is increased to the second stage temperature of 1000℃ at a heating rate of 0.2℃ / min and held for 12 h. The temperature is decreased to the third stage temperature of 700℃ at a cooling rate of 0.2℃ / min and held for 6 h. The temperature is increased to the fourth stage temperature of 1000℃ at a heating rate of 0.2℃ / min and held for 3 h. The temperature is decreased from the fourth stage temperature to room temperature at a cooling rate of 1℃ / min. After airflow pulverization, the proportion of small particles smaller than 1μm in the cathode material is 4.2%.

[0187] Comparative Example 4

[0188] Unlike Example 1,

[0189] (3) The oxide precursor and Li2CO3 are mixed at a molar ratio of Li / Me (Me is the sum of Ni, Co and Mn) of 1.05:1 and placed in an atmosphere electric furnace or Joule thermal reactor. An oxygen atmosphere is used and the reaction pressure is controlled at 10 Pa. The temperature is increased from room temperature to the first stage temperature of 900℃ at a heating rate of 20℃ / min and held for 8 hours. The temperature is increased to the second stage temperature of 700℃ at a heating rate of 3℃ / min and held for 2 hours. The temperature is then reduced to room temperature at a cooling rate of 3℃ / min. The material is then pulverized by airflow so that the proportion of particles smaller than 1μm in the cathode material is 20%.

[0190] Comparative Example 5

[0191] (1) Weigh nickel nitrate, cobalt nitrate and manganese nitrate into water and add them to prepare a metal salt mixed solution by adding 0.6% of H2SO4 relative to the total molar of Ni / Co / Mn metals into the mixed solution. Stir the solution with ultrasonic for 2 hours to ensure thorough mixing and obtain a mixed solution.

[0192] (2) The mixed solution was atomized using a plasma rotating electrode to form microparticles approximately 20 μm in size, which were then fed into a calcining furnace for thermal decomposition to prepare the oxide precursor. The first temperature zone was 400℃ with a residence time of 60 s; the second temperature zone was 1100℃ with a residence time of 3 s; and the third temperature zone was 700℃ with a residence time of 3 min. The oxygen volume concentration in the calcining furnace was controlled at 30%. The chemical formula of the oxide precursor is Ni. 0.60 Co 0.1 Mn 0.3 O, the oxide precursor is pulverized by airflow to a suitable particle size D50 = 3.0 μm, Dmax = 15.

[0193] (3) The oxide precursor and Li2CO3 are mixed at a molar ratio of Li / Me (Me is the sum of Ni, Co and Mn) of 1.05:1 and placed in an atmosphere electric furnace or Joule thermal reactor. An oxygen atmosphere is used and the reaction pressure is controlled at 10 Pa. The temperature is increased from room temperature to the first stage temperature of 900℃ at a heating rate of 20℃ / min and held for 8 hours. The temperature is increased to the second stage temperature of 700℃ at a heating rate of 3℃ / min and held for 2 hours. The temperature is then reduced to room temperature at a cooling rate of 3℃ / min. The material is then pulverized by airflow so that the proportion of particles smaller than 1μm in the cathode material is 20%.

[0194] The cathode materials of the above embodiments (abbreviated as S1 to S14) and comparative examples (abbreviated as D1 to D5) were subjected to physicochemical and electrochemical tests, and the test results are shown in Table 1 and Table 2 below.

[0195] Table 1: Comparison of cathode materials between the examples and comparative examples

[0196] Table 2: Electrochemical performance test results of the cathode materials in the examples and comparative examples

[0197] This application controls the enrichment of sulfur in the cathode material to ≤70%, and controls the proportion of particles with a diameter of less than 1 μm in the cathode material. The doping of sulfur atoms can improve the lattice rotation of the cathode material and enhance its structural stability. Controlling the proportion of particles with a diameter of less than 1 μm can reduce the side reactions between the cathode material and the electrolyte and improve the cycle performance of the cathode material. Under the synergistic effect of the two, the cathode material can have excellent structural stability and long cycle performance.

[0198] Compared with Example 1, due to the lower temperature in the second temperature zone, most of the sulfate ions in the mixed solution are enriched on the surface of the oxide precursor and have difficulty entering the interior of the oxide precursor, resulting in a significant increase in β, a decrease in the cycle stability of the cathode material, which is not conducive to the transport of lithium ions and an increase in internal resistance.

[0199] Compared with Example 1, Comparative Example 2 shows that due to the excessively high oxygen concentration during thermal decomposition, sulfate ions in the mixed solution are unable to replace oxygen in the crystal lattice, resulting in a significant increase in β. This leads to a decrease in the cycle stability of the cathode material, which is not conducive to the transport of lithium ions and increases the internal resistance.

[0200] Compared with Example 1, Comparative Example 3 shows that due to the low proportion of particles with a diameter of less than 1 μm in the cathode material, the lithium ion transport path is extended, the initial DCR of the cathode material increases, and the compaction density of the cathode material decreases.

[0201] Compared with Example 1, Comparative Example 4 showed that the positive electrode material had a higher proportion of particles with a diameter of less than 1 μm, which aggravated the side reactions between the positive electrode material and the electrolyte, resulting in a decrease in the cycle stability of the positive electrode material.

[0202] Compared with Example 1, Comparative Example 5 had too much dilute sulfuric acid added to the mixed solution. The excessive sulfur element also inhibited the growth of primary particles, increased the proportion of particles with a diameter of less than 1 μm in the cathode material, aggravated the side reactions between the cathode material and the electrolyte, significantly increased the β of the cathode material, increased the initial DCR of the cathode material, and significantly decreased the cycle stability of the cathode material.

[0203] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A positive electrode material, characterized in that, The surface enrichment of sulfur in the cathode material is β = A2 / A1, β% ≤ 70%, A1 is the total mass content of sulfur in the cathode material, and A2 is the mass content of sulfur in the free sulfate ions of the cathode material; in the scanning electron microscope (SEM) image of the cathode material, the proportion of particles with a diameter of less than 1 μm in the cathode material is 6% to 18%.

2. The cathode material according to claim 1, characterized in that, The general chemical formula of the cathode material is Li. x Ni a Co b N c M1 d O2, wherein 0.98≤x≤1.1, 0.5≤a≤0.98, 0<b≤0.2, 0<c≤0.30, 0≤d≤0.1, a+b+c+d=1, the N element includes at least one of Mn and Al, and the M1 element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y.

3. The cathode material according to claim 1, characterized in that, The total mass content A1 of sulfur in the cathode material satisfies 50ppm≤A1≤1000ppm.

4. The cathode material according to claim 1, characterized in that, The mass content A2 of sulfur in the surface free sulfate ions of the cathode material satisfies 0ppm < A2 ≤ 700ppm.

5. The positive electrode material according to claim 1, characterized in that, The cathode material includes primary particles and a coating layer located on at least a portion of the surface of the primary particles. The coating layer includes element M2, which includes at least one of Al, Ti, Zr, Y, Nb, Mg, W, B, Ce, Co, and Mn.

6. The cathode material according to claim 1, characterized in that, The cathode material is a single-crystal cathode material.

7. The cathode material according to claim 1, characterized in that, The median particle size of the cathode material is 1.5 μm to 5.0 μm.

8. The positive electrode material according to claim 1, characterized in that, The specific surface area of ​​the positive electrode material is 0.5 m². 2 / g~1.2m 2 / g.

9. The positive electrode material according to claim 1, characterized in that, The compaction density of the positive electrode material is 3.0 g / cm³. 3 ~3.3g / cm 3 .

10. The cathode material according to claim 1, characterized in that, The cathode material satisfies at least one of the following conditions: (1) During the first charge and discharge cycle, the structural recovery degree δ of the positive electrode material satisfies: 99.7% ≤ δ ≤ 100.0%; where δ = θ1 / θ2 * 100%, θ1 is the diffraction angle of the positive electrode material at the (003) crystal plane diffraction peak measured by X-ray diffraction at the beginning of the first charge cycle, and θ2 is the diffraction angle of the positive electrode material at the (003) crystal plane diffraction peak measured by X-ray diffraction at the end of the first discharge cycle; (2) The positive electrode material is prepared into a mold battery and characterized by in-situ XRD. The structural recovery degree δ of the positive electrode material satisfies: 99.7% ≤ δ ≤ 100.0%; where δ = θ1 / θ2 * 100%, θ1 is the diffraction angle of the positive electrode material at the (003) crystal plane diffraction peak measured by X-ray diffraction at the beginning of the first cycle of charging, and θ2 is the diffraction angle of the positive electrode material at the (003) crystal plane diffraction peak measured by X-ray diffraction at the end of the first cycle of discharge.

11. The cathode material according to claim 1, characterized in that, The surface enrichment β of sulfur in the cathode material satisfies any one of the following conditions: (1)40％≤β≤50％； (2)50％≤β≤70％； (3) β can be within the range of 70%, 65%, 60%, 50%, 45%, 40%, 30%, 25%, 20%, 10% or any combination of the above.

12. The cathode material according to claim 1, characterized in that, The cathode material satisfies any one of the following conditions: (1) The proportion of particles with a diameter of less than 1 μm in the positive electrode material is 12% to 15%; (2) The proportion of particles with a diameter of less than 1 μm in the positive electrode material is 15% to 18%; (3) The proportion of particles with a diameter of less than 1 μm in the positive electrode material can be 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 18% or any combination thereof.

13. The cathode material according to claim 1, characterized in that, The cathode material comprises primary particles, the average particle size of which is 1µm to 5µm.

14. A positive electrode plate, characterized in that, The positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 13.

15. A battery, characterized in that, The battery comprises the positive electrode material as described in any one of claims 1 to 13 or the positive electrode sheet as described in claim 14.

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