Cathode materials and preparation methods and lithium-ion batteries

Abstract

This invention provides a cathode material, a preparation method thereof, and a lithium-ion battery. The general chemical formula of the cathode material provided in this application is Li. x Ni a Co b Mn c N d O2, where 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, and free SO4 in the cathode material. 2‑ The content of SO4 is ≤800ppm. 2‑ The surface enrichment degree is ≤70%. The free SO4 in the cathode material provided in this application... 2‑ The content of SO4 is ≤800ppm. 2‑ Surface enrichment ≤70%; some SO4 2‑ SO42- doped into the internal crystal lattice, in the bulk phase 2‑ Suppressing c-axis contraction reduces the activation energy of Li migration, thereby improving the cycle performance and rate performance of the cathode material.

Description

Technical Field

[0001] This invention relates to the field of cathode material technology, and more specifically, to a cathode material, a method for preparing it, and a lithium-ion battery. Background Technology

[0002] Cathode materials possess high energy density and are among the mainstream cathode materials for power lithium batteries, widely used in mid-to-high-end new energy vehicles. Cathode materials are typically prepared by high-temperature sintering of precursor compounds containing Ni, Co, and Mn with lithium salts. However, existing cathode materials exhibit poor rate performance and cycle stability.

[0003] In view of the above, this application is hereby submitted. Summary of the Invention

[0004] The main objective of this invention is to provide a cathode material precursor, a cathode material, a preparation method thereof, and a lithium-ion battery, so as to solve the problem of poor rate performance and cycle stability of cathode materials in the prior art.

[0005] To achieve the above objectives, according to a first aspect of the present invention, a cathode material is provided, the cathode material having the general chemical formula Li. x Ni a Co b M c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, M element includes at least one of Mn or Al, N element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y, and free SO4 in the cathode material. 2- The content is ≤800ppm, and SO4 2- The surface enrichment is ≤70%.

[0006] According to a second aspect of the present invention, a method for preparing a cathode material is also provided, the method comprising: sequentially subjecting a mixed solution of metal salts containing Ni salt, Co salt, Mn salt and N salt to atomization and pyrolysis to obtain a cathode material precursor; mixing the cathode material precursor and a lithium source and sintering to obtain the cathode material; wherein the general formula of the cathode material precursor is Ni a Co b Mn c N d O eWherein, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.35, 0≤d≤0.10, a+b+c+d=1, 1≤e≤1.15, N element, N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; the general chemical formula of the positive electrode material is Li x Ni a Co b Mn c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, and the N element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn, and Y; the positive electrode material contains free SO4. 2- The content is ≤800ppm, and SO4 2- The surface enrichment is ≤70%.

[0007] According to a third aspect of the present invention, a lithium-ion battery is also provided, comprising the positive electrode material provided in the first aspect or the positive electrode material obtained according to the preparation method provided in the second aspect.

[0008] Applying the technical solution of this application, the positive electrode material provided by this application contains free SO4 2- The content is ≤800ppm, and SO4 2- Surface enrichment ≤70%; some SO4 2- SO42- doped into the internal crystal lattice, in the bulk phase 2- It can suppress c-axis contraction, reduce the activation energy of Li migration, thereby increasing the migration rate of Li, suppress heterogeneous reactions, reduce lattice rotation, and thus improve the cycle performance and rate performance of cathode materials. Attached Figure Description

[0009] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0010] Figure 1 The Williamson-Hall analysis fitting curve of the cathode material according to Embodiment 1 of the present invention is shown;

[0011] Figure 2 A SEM image of the cathode material according to Embodiment 1 of the present invention is shown. Detailed Implementation

[0012] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0013] As described in the background section of this application, existing cathode materials exhibit poor rate performance and cycle stability. To address this issue, this application provides a cathode material, a method for its preparation, and a lithium-ion battery.

[0014] In a first typical embodiment of this application, a positive electrode material is provided, the chemical formula of which is Li x Ni a Co b M c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, M element includes at least one of Mn or Al, N element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; the free SO4 of the cathode material 2- The content is ≤800ppm, and SO4 2- The surface enrichment is ≤70%.

[0015] In this application, SO4 2- Surface enrichment refers to free SO4 2- Content and SO4 in cathode materials 2- The ratio of total content.

[0016] Free SO4 in cathode materials 2- It has a significant impact on the electrochemical performance of materials, when free SO4 2- High SO4 content can lead to a deterioration in material capacity and rate capability. The cathode material provided in this application contains free SO4. 2- The content is ≤800ppm, and SO4 2- The surface enrichment of SO4 is ≤70%, indicating that some SO4 is present. 2- SO42- doped into the internal crystal lattice, in the bulk phase 2- It can suppress c-axis contraction, reduce the activation energy of Li migration, thereby increasing the migration rate of Li, suppress heterogeneous reactions, reduce lattice rotation, and thus improve the cycle performance and rate performance of cathode materials.

[0017] Typically, but not limitingly, in the cathode material provided in this application, the value of x can be 0.98, 0.99, 1.0, 1.01, 1.03, 1.05, 1.08, 1.09, 1.1, or any range of two values; the value of a can specifically be 0.50, 0.55, 0.60, 0.63, 0.70, 0.75, 0.80, 0.85, 0.88, 0.90, 0.95, 0.98, or any range of two values; the value of b can be 0.01, 0.05, ... The values ​​of c can be 0.08, 0.10, 0.11, 0.13, 0.15, 0.18, 0.20, or any two of these values; the values ​​of c can be 0.01, 0.05, 0.10, 0.15, 0.18, 0.20, 0.23, 0.27, 0.30, or any two of these values; the values ​​of d can be 0, 0.01, 0.03, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, or any two of these values; the free SO4 in the positive electrode material. 2- The content is such as 100ppm, 200ppm, 300ppm, 400ppm, 500ppm, 550ppm, 600ppm, 650ppm, 700ppm, 750ppm, 800ppm, or any range of two values; SO4 2- The surface enrichment can be 10%, 20%, 30%, 40%, 50%, 55%, 60%, 65%, 70%, or any range of two values.

[0018] In some embodiments, under a 6T pressure, the volume percentage of particles smaller than 1μm in the cathode material is ≤4%. The presence of an appropriate amount of microparticles within the cathode material allows these microparticles to fill the gaps between the particles, thereby improving cycle stability. If the volume percentage of particles smaller than 1μm in the cathode material is too high, the microparticle content is excessive, resulting in an excessively large specific surface area. This can cause reactions between the solution and the electrolyte, thus affecting cycle stability. Specifically, under a 6T pressure, the volume percentage of particles smaller than 1μm in the cathode material is, for example, 0%, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or any combination of two values.

[0019] In some embodiments, the lattice strain of the cathode material is ≤0.2% to improve the structural stability of the cathode material, reduce the probability of particle cracking during cycling, and thus improve its cycling stability. Specifically, the lattice strain of the cathode material can be 0.01%, 0.03%, 0.05%, 0.08%, 0.10%, 0.11%, 0.12%, 0.15%, 0.18%, 0.19%, 0.2%, or any range of two values.

[0020] In some embodiments, the cathode material further includes a coating layer comprising at least one element selected from Al, Ti, Zr, Y, Nb, Mg, W, B, Ce, Co, and Mn. The coating layer helps reduce direct contact between the cathode material and the electrolyte, reduces side reactions between them, and improves cycle performance, rate performance, and DCR (DC internal resistance).

[0021] In some embodiments, the particle size D50 of the cathode material is 2.5 μm-5 μm to improve the compaction density for forming the cathode, thereby enhancing its electrochemical performance. Specifically, the volume distribution D50 of the cathode material precursor can be 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, or any range of two values.

[0022] In some embodiments, the particle size Dmin of the cathode material is greater than 0.3 μm. Smaller particle size of the cathode material is more conducive to improving its particle strength; however, excessively small particle size is detrimental to improving its electrochemical performance. Specifically, the volume distribution Dmin of the cathode material precursor can be 0.35 μm, 0.40 μm, 0.45 μm, 0.50 μm, 0.55 μm, 0.6 μm, or any combination of two values ​​within a range.

[0023] In some embodiments, the particle size Dmax of the cathode material is <14 μm. Excessively large particle size of the cathode material is detrimental to increasing its compaction density, and consequently, to improving its electrochemical performance. Specifically, the volume distribution Dmax of the cathode material precursor can be 13.9 μm, 13 μm, 12 μm, 11 μm, 10 μm, 9 μm, or any combination of two values ​​within a range.

[0024] In some embodiments, the specific surface area of ​​the cathode material is 0.5-1.2 m². 2 / g. If the specific surface area of ​​the cathode material is too large, its electrochemical performance will be poor; if the specific surface area is too small, it will be detrimental to improving its compaction density. Therefore, selecting a cathode material with an appropriate specific surface area is more conducive to improving the electrochemical performance of the cathode material. Specifically, the specific surface area of ​​the cathode material can be 0.5m². 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g or a range of values ​​consisting of any two numbers.

[0025] In some embodiments, the pH of the positive electrode material satisfies 11.0 ≤ pH ≤ 12.0. If the pH of the positive electrode material is too low, it is not conducive to stable dispersion in the slurry; if the pH of the positive electrode material is too high, the alkalinity is too great, which is not conducive to improving the stability of the positive electrode sheet. Specifically, the pH of the positive electrode material can be 11.0, 11.2, 11.5, 11.8, 12.0, or any range of two values.

[0026] In some embodiments, the cathode material is a single-crystal material comprising grains with the same orientation. The grain size is 1 μm to 5 μm, which helps to improve the stability of the cathode material during cycling, reduce the probability of cracking, and thus improve its cycling stability. Specifically, the grain size can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, or any range of two values.

[0027] It is important to clarify that the difference between single-crystal cathode materials and polycrystalline cathode materials (i.e., polycrystalline secondary particles) lies in the fact that polycrystalline secondary particles are secondary particles formed by the agglomeration of nanoscale primary particles. Single-crystal cathode materials, on the other hand, are typically micrometer-sized single primary particles. Generally, the determination of whether the obtained cathode product is a single-crystal material can be made using testing methods such as SEM and EBSD. For example, for single-crystal cathode materials, the morphology of single-crystal particles can be characterized by SEM; under SEM, single-crystal particles generally appear as regular or irregular spheres with no significant particle agglomeration. EBSD is commonly used to characterize the orientation of the crystal structure. EBSD can also be used to characterize the orientation of single-crystal cathode materials; by observing that most grains of a single-crystal cathode material have the same color, it indicates that most grains are single primary particles with the same orientation. 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 such as impurities, strain, and crystal defects, ideal single crystals are very rare and difficult to produce in the laboratory. Therefore, the single-crystal cathode materials known in the art are actually more "single-crystal-like" cathode materials, which only differ from polycrystalline materials composed of numerous small primary particles in size, exhibiting a large particle size similar to single crystals.

[0028] In a second typical embodiment of this application, a method for preparing a cathode material is also provided. This method includes: step S1, adding an appropriate amount of H2SO4 to a mixed solution containing Ni salt, Co salt, Mn salt, and N salt to obtain a mixed solution; step S2, atomizing and pyrolyzing the mixed solution to obtain a pyrolytic cathode material precursor; and step S3, mixing the cathode material precursor with a lithium source and sintering to obtain the cathode material. The general formula of the cathode material precursor is Ni... a Co bMn c N d O e Wherein, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.35, 0≤d≤0.10, a+b+c+d=1, 1≤e≤1.15, N is a doping element, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; the general chemical formula of the cathode material is Li x Ni a Co b M c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, M element includes at least one of Mn or Al, N element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; the free SO4 of the cathode material 2- The content is ≤800ppm, and SO4 2- Surface richness ≤70%.

[0029] Therefore, this application adds a certain amount of H2SO4 during the preparation of the cathode material precursor to mix the solution, so that some of the SO4 is released during the atomization and pyrolysis process. 2- It can be doped into the bulk phase, thereby enabling the preparation of free SO4. 2- The content is ≤800ppm, and SO4 2- A cathode material with a surface enrichment of ≤70% can improve the cycle performance and rate performance of the cathode material.

[0030] In some embodiments, the molar ratio of Ni, Co, M, and N in the metal salt mixed solution is (50-98):(0-20):(0-35):(0-0.10), and neither Co nor M is 0. Specifically, the molar ratio of Ni, Co, and M in the metal salt mixed solution can be 50:0.1:0.1, 60:10:30, 65:15:20, 65:5:30, 70:5:25, 70:10:20, 80:5:15, 85:10:5, 98:1:1, or any range of two values. The molar ratios of Ni, Co, M, and N can be 50:0.1:0.1:0.01, 60:10:30:0.02, 65:15:20:0.05, 65:5:30:0.08, 70:5:25:0.1, 70:10:20:0.1, 80:5:15:0.01, 85:10:5:0.1, 98:1:1:0.05, or any range of two values.

[0031] In some embodiments, the concentration of total metals in the metal salt mixed solution is 100 g / L to 500 g / L, wherein the total metals include Ni, Co, M, and N. Specifically, the concentration of total metals in the metal salt mixed solution can be 200 g / L, 220 g / L, 260 g / L, 300 g / L, 350 g / L, 400 g / L, 450 g / L, 480 g / L, 500 g / L, or any range of two such values.

[0032] In some embodiments, in a metal salt mixed solution, based on the total mass of Ni, Co, Mn, and N elements, SO4 2- The content is ≤2400ppm. Specifically, in a mixed solution of metal salts, SO42- 2- The content can be 2400ppm, 2300ppm, 2200ppm, 2100ppm, 2000ppm, 1800ppm, 1500ppm, 1300ppm, 1100ppm, 800ppm or any range of two values.

[0033] In step S2, the mixed solution is atomized through a plasma rotating electrode to form microparticles of 2–200 μm in size, which are then pyrolyzed in a calcination furnace to obtain the precursor. By controlling the size of the atomized droplets, precursor particles of suitable size are formed after atomization, which is beneficial for SO42-. 2- Doping is introduced into the interior of the crystal lattice.

[0034] In some embodiments, the pressure of the atomization process is 0.4 MPa to 0.8 MPa. Specifically, the pressure of the atomization process can be 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.75 MPa, 0.8 MPa, or any range of two values.

[0035] In step S2, the atomized droplets pass sequentially through two temperature zones of the calcining furnace. The first temperature zone has a temperature of 1000-1200℃, and the material stays in this zone for 2-10 seconds to prevent the precursor particles from growing too large and affecting the reactivity of the precursor. The brief high temperature also promotes the doping of sulfur. The second temperature zone has a pyrolysis temperature of 500-800℃, which promotes the further decomposition of the metal salt to form an oxide precursor.

[0036] The size of the precursor particles is related to the pyrolysis temperature of the first temperature zone; the higher the temperature, the larger the precursor particles. In some embodiments, in step S2, the temperature of the first temperature zone is controlled at 1000-1200℃, and the residence time is 2-10s to facilitate the pyrolysis of precursor particles with suitable particle size, and also to promote the decomposition of SO4. 2- The dopant is incorporated into the crystal lattice. Specifically, the pyrolysis temperature of the first temperature zone can be controlled to be 1000℃, 1020℃, 1050℃, 1080℃, 1200℃, or any range of two values.

[0037] When the temperature in the first temperature zone is too high, the precursor particles formed are too large, resulting in low particle strength and large lattice strain in the prepared cathode material. When the temperature is too low, SO42-... 2- It is difficult to dope into the interior of the crystal lattice.

[0038] SO4 2- Due to their large ionic radii, it is very difficult to dope them into the crystal lattice of the precursor or cathode material during actual synthesis. In this invention, the applicant discovered through extensive experiments that by controlling the O2 content in the calcination furnace to ≤12%, the SO4 content of the precursor can be reduced. 2- The surface enrichment was significantly reduced; the likely reason is that when the O2 volume content is ≤15%, a reducing atmosphere is easily formed in the roasting furnace. In a reducing atmosphere, some SO4... 2- The medium energy can be reduced to S 2- Low-valence ions are more easily introduced into the crystal lattice inside the cathode material precursor. Specifically, in the pyrolysis atmosphere, the volume content of O2 can be 0, 1%, 2%, 5%, 8%, 9%, 10%, 11%, 12%, or any combination of two values.

[0039] In some embodiments, the specific type of lithium source is not limited, and any commonly used lithium-containing compound in the art can be used, including but not limited to at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium sulfate, lithium chloride, lithium nitrate, and lithium oxalate.

[0040] In some embodiments, the molar ratio of lithium in the lithium source to the total metal in the cathode material precursor is 0.98-1.10; wherein the molar ratio of the total metal in the cathode material precursor is the sum of the molar ratios of Ni, Co, Mn, and N in the cathode material precursor. Specifically, the molar ratio of lithium in the lithium source to the total metal in the cathode material precursor is a range of 0.98, 0.99, 1.01, 1.03, 1.05, 1.06, 1.08, 1.09, 1.10, or any two of these values.

[0041] In some embodiments, in step S3, the sintering atmosphere is an oxygen-containing atmosphere with an O2 volume content ≥95%, which facilitates the provision of an oxidizing atmosphere for oxidative sintering of the cathode material precursor and the lithium source, thereby preparing a cathode material with a more stable layered structure. Specifically, in the sintering atmosphere, the O2 volume content can be 95%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 99%, 100%, or any range of two values.

[0042] In some embodiments, in step S3, the sintering temperature is 750-980℃, and the sintering time is 10h-30h, which helps to reduce crystal structure defects in the cathode material, reduce lattice strain, control particle size distribution, and thus improve the electrochemical performance of the cathode material. Specifically, the sintering temperature can be 750℃, 760℃, 780℃, 800℃, 850℃, 900℃, 920℃, 950℃, 980℃, or any range of two such values; the sintering time can be 10h, 12h, 15h, 16h, 18h, 20h, 24h, 28h, 30h, or any range of two such values.

[0043] In a third typical embodiment of this application, a lithium-ion battery is also provided, which includes the positive electrode material provided in the first typical embodiment or the positive electrode material obtained by the preparation method provided in the second typical embodiment.

[0044] The lithium-ion battery provided in this application uses free SO4. 2- The content is ≤800ppm, and SO4 2- Cathode materials with a surface enrichment of ≤70% exhibit excellent cycle performance and rate performance.

[0045] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0046] Example 1

[0047] This embodiment provides a cathode material, which is prepared according to the following steps:

[0048] (1) Mole bis (n) Ni :n Co :n Mn =0.60:0.1:0.3) Weigh out nickel nitrate, cobalt nitrate, and manganese nitrate and add them to water to prepare a mixed metal salt solution. Control the total metal concentration in the mixed metal salt solution to be 300 g / L. Add H2SO4 to adjust the SO4 concentration in the mixed solution. 2- The mass ratio relative to the total metal is 1200 ppm, where the total metal mass refers to the sum of the masses of Ni, Co, and Mn elements in the metal salt mixture solution.

[0049] (2) After the metal salt mixed solution is atomized into droplets by a plasma rotating electrode, it is placed in a pyrolysis atmosphere and pyrolyzed in a calcination furnace through the first and second temperature zones. The solid obtained from pyrolysis is pulverized by airflow to obtain the cathode material precursor. The chemical formula of the cathode material precursor is Ni. 0.60 Co 0.1 Mn 0.3 O; wherein, the volume concentration of O2 in the pyrolysis atmosphere is controlled at 8%, and during the atomization process, the flow rate is controlled at 200L / h, the atomization pressure is 0.6MPa, the heating temperature of the first temperature zone is 1100℃, the material residence time is 5s, the heating temperature of the second temperature zone is 750℃, and the residence time is 60s.

[0050] (3) After the cathode material precursor is mixed evenly with lithium hydroxide, it is heated to 930°C under an oxygen atmosphere and sintered for 20 hours to obtain the cathode material LiNi. 0.60 Co 0.1 Mn 0.3 O2. The molar ratio of lithium hydroxide to the total metal in the cathode material precursor is 1:1. The total molar amount of metal in the cathode material precursor refers to the sum of the molar amounts of Ni, Co, and Mn elements.

[0051] Example 2

[0052] The difference between this embodiment and Embodiment 1 is that, in step (1), SO4 in the metal salt mixed solution... 2- The mass ratio relative to the total metals is 500 ppm.

[0053] Example 3

[0054] The difference between this embodiment and Embodiment 1 is that, in step (1), SO4 in the metal salt mixed solution... 2- The mass ratio relative to the total metals is 1500 ppm.

[0055] Example 4

[0056] The difference between this embodiment and Embodiment 1 is that, in step (1), SO4 in the metal salt mixed solution... 2- The mass ratio of the total metal is 900 ppm, and in step (2), the heating temperature of the first temperature zone is 1000℃, the material residence time is 5s, the temperature of the second temperature zone is pyrolysis 750℃, and the volume concentration of O2 in the pyrolysis atmosphere is 11%.

[0057] Example 5

[0058] The difference between this embodiment and embodiment 1 is that in step (2), the heating temperature of the first temperature zone is 1200℃, the material residence time is 9s, the temperature of the second temperature zone is pyrolysis 750℃, and the volume concentration of O2 in the pyrolysis atmosphere is 5%.

[0059] Example 6

[0060] The difference between this embodiment and Embodiment 1 is that, in step (1), SO4 in the metal salt mixed solution... 2- The mass ratio relative to the total metal is 2400 ppm. In step (2), the heating temperature of the first temperature zone is 1100℃, the material residence time is 5s, the temperature of the second temperature zone is pyrolysis 8750℃, and the volume concentration of O2 in the pyrolysis atmosphere is 6%.

[0061] Example 7

[0062] The difference between this embodiment and embodiment 1 is that in step (2), the heating temperature of the first temperature zone is 1000℃, the material residence time is 2s, the temperature of the second temperature zone is 500℃, and the volume concentration of O2 in the pyrolysis atmosphere is 12%.

[0063] Example 8

[0064] The difference between this embodiment and Embodiment 1 is that, in step (1), the molar ratio of nickel, cobalt, and manganese is n. Ni :n Co :n Mn =0.90:0.05:0.05, in step (3), the sintering temperature is 750℃ and the sintering time is 30h. The sintering atmosphere is an oxygen-containing atmosphere with an O2 volume concentration of 99%.

[0065] Example 9

[0066] The difference between this embodiment and Embodiment 1 is that, in step (1), the molar ratio of nickel, cobalt, and manganese is n. Ni :n Co :n Mn =0.55:0.10:0.25, in step (3), the sintering temperature is 980℃ and the sintering time is 10h. The sintering atmosphere is an oxygen-containing atmosphere with an O2 volume concentration of 95%.

[0067] Example 10

[0068] The difference between this embodiment and embodiment 1 is that, in step (1), the total metal concentration in the metal salt mixed solution is 100 g / L, and in step (2), the pressure of the atomization treatment is 0.4 MPa.

[0069] Example 11

[0070] The difference between this embodiment and embodiment 1 is that, in step (1), the total metal concentration in the metal salt mixed solution is 500 g / L, and in step (2), the pressure of the atomization treatment is 0.8 MPa.

[0071] Example 12

[0072] The difference between this embodiment and embodiment 8 is that, in step (1), the molar ratio (n) Ni :n Co :n Al =0.90:0.05:0.05) Weigh out nickel nitrate, cobalt nitrate, and aluminum nitrate and add them to water to prepare a mixed solution of metal salts.

[0073] Comparative Example 1

[0074] The difference between this comparative example and Example 1 is that in step (2), the volume concentration of O2 in the pyrolysis atmosphere is 25%, and only the second temperature zone is set, with the heating temperature of the second temperature zone being 750°C.

[0075] Comparative Example 2

[0076] The difference between this comparative example and Example 1 is that, in step (1), the metal salt mixed solution contains SO4. 2- With a total metal mass ratio of 650 ppm, in step (2), the volume concentration of O2 in the pyrolysis atmosphere is 25%, and only the second temperature zone is set, with a heating temperature of 750 °C.

[0077] Comparative Example 3

[0078] The difference between this comparative example and Example 1 is that, in step (1), the metal salt mixed solution contains SO4. 2- The mass ratio relative to the total metals is 2900 ppm.

[0079] Comparative Example 4

[0080] The difference between this comparative example and Example 1 is that, in step (2), the volume concentration of O2 in the pyrolysis atmosphere is 15%.

[0081] Comparative Example 5

[0082] The difference between this comparative example and Example 1 is that in step (2), the temperature of the first temperature zone is 1400°C and the volume concentration of O2 in the pyrolysis atmosphere is 15%.

[0083] Experimental Example 1

[0084] The cathode material precursors and cathode materials prepared in the examples and comparative examples were analyzed for particle size D50, grain size, pH value, and free SO4. 2- Content, SO4 2- The total amount and surface enrichment were tested, and the results are shown in Table 1 below. In addition, the lattice strain of the cathode materials prepared in the examples and comparative examples was measured, and the results are shown in Table 1 below.

[0085] Among them, (1) the particle size determination method is: the average particle size D50 of the volumetric fabric of the cathode material precursor or cathode material is obtained by using a Malvern 3000 laser particle size analyzer.

[0086] (2) The method for testing grain size is as follows: cross-section samples were prepared using an ion cutter, and the cross-section morphology was tested using a Hitachi S4800 scanning electron microscope. Ten photos were taken at 5K magnification. All images were imported into the software Nano Measure to count the size of the single crystal particles.

[0087] (3) The pH test method is as follows: The pH of the positive electrode material is tested using a METTLER TOLEDO FE28. The specific process is as follows: Take about 5g of positive electrode material sample, add 45mL of water, sonicate for 5min, and then let it stand for 10min. After calibrating the pH meter, insert the composite electrode into the supernatant solution to be tested. Calculate the pH value of the solution based on the potential difference between the measuring electrode and the reference electrode.

[0088] (4) The method for determining the lattice strain is as follows: the lattice strain of the cathode material is calculated from the XRD data using Williamson-Hall analysis. Specifically, it is measured using a Rigaku X-ray diffractometer (Japan), with the following conditions: 0.75 degrees / minute, step size 0.02, and continuous scanning within the 2θ range from 10 to 90 degrees. The lattice strain is plotted using a 4sinθ... hkl Let β be the x-axis. hkl cosθ hklUsing the vertical axis as the ordinate, a curve is plotted and linearly fitted. The strain ε can be calculated from the slope. It is worth mentioning that the half-width at half maximum (WHM) βhkl used for fitting needs to eliminate the influence of the instrument, i.e., βhkl = βtotal - βinstrument, where βtotal is the actual measured WHM value, and βinstrument is the WHM broadening caused by the instrument. This value can be calculated by XRD of the test standard silicon wafer. The βinstrument of the test equipment used in this application is 0.000103. In addition, the data of seven strong diffraction peaks (003), (101), (102), (104), (015), (107), and (113) are selected for fitting to improve the linear fitting degree and reduce the actual test error.

[0089]

[0090] 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.

[0091] (5) Volume ratio test of 1μm cathode material particles under 6T pressure: 1g sample was placed in the mold of the compaction density meter (Carver 4350, USA) and pressed for 30s with 6T pressure. The sample was then taken out and the volume ratio of 1μm particles was tested using a Malvern 3000 laser particle size analyzer.

[0092] (6) The method for determining the content of free anions is as follows: take 0.5 g and dissolve it in 50 ml of water, sonicate for 5 min and filter. Then, measure the content of free ions such as F / Cl / SO4 in the filtrate using ion chromatography (Thermo Fisher ICS6000 HPIC).

[0093] (7) SO4 2- The method for determining the total content is as follows: a certain amount of sample is digested with aqua regia, cooled and brought to a final volume, and the content of sulfur (S) is measured using an Agilent 5110 ICP-OES spectrometer, recorded as ms; SO4 2- Total content = ms × SO4 2- The molecular weight of S / the molecular weight of S.

[0094] Table 1

[0095]

[0096] Figure 1 The Williamson-Hall analysis fitting curve of the cathode material provided in Example 1 is shown. Figure 1It can be seen that there is a good linear relationship between βcosθ and 4sinθ. The lattice strain of the cathode material prepared in Example 1 is the slope of the fitted straight line, which is 0.1%, indicating that the lattice strain of the cathode material prepared in the example is less than 0.2%.

[0097] Figure 2 SEM images of the cathode material provided in Example 1 are shown. Figure 2 It can be seen that the cathode material prepared in Example 1 mainly exhibits a single crystal morphology.

[0098] Experimental Example 2

[0099] The electrochemical performance of the cathode materials prepared in the above examples and comparative examples was evaluated using coin cell half-cells. The specific procedure was as follows: Cathode material, conductive carbon black, and polyvinylidene fluoride (PVDF) were weighed in a mass ratio of 93:5:2. N-methyl-2-pyrrolidone (NMP) was added at a solid content of 50%, and the mixture was prepared into a viscous slurry using a high-speed disperser. This slurry was then uniformly coated onto aluminum foil using a scraper, dried in an oven at 80°C, rolled, and cut into cathode sheets with a diameter of 14 mm. A 16 mm lithium sheet was used as the anode, a Celgard polypropylene membrane as the separator, and a 1 mol / L LiPF6 carbonate solution as the electrolyte. The cells were assembled in an argon-filled glove box to obtain coin cell half-cells. Capacity and cycle performance tests were conducted using a LAND battery testing system at 25°C and 3.0-4.4 V (except for Example 8, whose voltage range was 3.0-4.3 V). The nominal capacity at 2C was set to 200 mAh / g. In addition, record the voltage U at the beginning of each weekly discharge. A And the voltage data U at 60s B Discharge current I Dis The formula for calculating DC internal resistance is DCR = (U A -U B ) / I Dis The test results are shown in Table 2 below.

[0100] Table 2

[0101]

[0102] Referring to Tables 1 and 2, the free SO4 in Examples 1-12 of this invention 2- The content is ≤800ppm, and SO4 2- The surface enrichment of the cathode material is ≤70%, and its cycle performance and capacity are significantly better than those of comparative examples 1-4. Tests yielded free SO4 in the cathode material provided in this application. 2- The content is ≤800ppm, and SO4 2- The surface enrichment degree is ≤70%; indicating that some SO4 is present. 2-Doping into the internal lattice suppresses c-axis contraction, lowers the activation energy for Li migration, and thus improves the cycle performance and rate performance of the cathode material, while also counteracting free SO4. 2- The negative impacts it brings.

[0103] Compared with Example 1, Example 2 reduces the amount of SO4 in the metal salt solution in step (1). 2- The content of free SO4 in the prepared cathode material 2- The content decreased, while SO4 2- The enrichment degree remained basically unchanged, and the cycle performance and rate performance of the cathode material were good, indicating that under a certain amount of SO4, 2- Based on doping, reduce free SO4 2- The increased SO4 content is beneficial for improving the electrochemical performance of the cathode material. In Example 3, the SO4 content of the metal salt solution in step (1) was increased. 2- The content of free SO4 2- Content and SO4 2- The enrichment of free SO4 increased, but the cycle performance and rate performance of the cathode material decreased. 2- Excessive content can affect the cycle performance and rate performance of the cathode material.

[0104] Compared to Example 1, Example 4 reduces the SO4 content of the metal salt solution in step (1). 2- The content of SO42-3 decreased the heating temperature and material residence time in the first temperature zone, resulting in a higher concentration of free SO42-3 in the cathode material. 2- Content and SO4 2- The enrichment degree of free SO42- increased, but the cycle performance and rate performance of the cathode material were poor. This indicates that increasing the enrichment degree of free SO42-... 2- The content of SO4 decreased at the same time 2- The doping amount is detrimental to improving the electrochemical performance of the cathode material. In Example 5, the heating temperature of the first temperature zone was increased, and the material residence time in the first temperature zone was extended, resulting in a cathode material with free SO4. 2- The content decreased, and SO4 2- The enrichment level of SO42- has increased, and the cycle performance and rate performance of the cathode material are good, indicating that the enrichment of free SO42- has been reduced. 2- The content of SO4 increases simultaneously 2- The doping amount can further suppress c-axis contraction, reduce the activation energy of Li migration, and thus improve the cycle performance and rate performance of the cathode material, and counteract free SO4. 2- The negative impacts it brings.

[0105] Compared to Example 1, Examples 4-6 changed the heating temperature and material residence time in the first temperature zone, resulting in a change in the volume percentage of particles smaller than 1 μm in the obtained cathode material at 6t. In Example 5, the heating temperature in the first temperature zone was 1200℃, which was higher than the heating temperatures in Examples 4 and 6, and the material residence time was 9s, which was also longer than the residence times in Examples 4 and 6. The resulting cathode material had a particle volume percentage of 4% smaller than 1 μm at 6t, and the obtained cathode material exhibited good cycle performance and rate performance, indicating that the presence of a certain amount of micronized powder can increase the cycle stability and rate performance of the cathode material.

[0106] In Comparative Examples 1 and 2, the volume concentration of O2 in the pyrolysis atmosphere was 25%, and only the second temperature zone was set. The resulting positive electrode material contained SO4. 2- The surface enrichment rate was as high as 90%, indicating that SO4 in the precursor solution was high. 2- It is difficult to reduce S to S. 2- The presence of low-valence ions and a relatively low pyrolysis temperature leads to SO42- 2- It is difficult to incorporate SO4 into the bulk phase, resulting in SO4 content within the cathode material. 2- The inability to suppress c-axis contraction results in poor cycle performance and rate performance of the cathode material.

[0107] In Comparative Example 3, the SO4 in the solution in step (1) 2- If the concentration is too high, the resulting cathode material will contain free SO4. 2- The concentration was 832 ppm. During the circulation process, free SO4... 2- It easily reacts with the electrolyte, leading to poor cycle stability of the cathode material. In Comparative Example 4, the volume concentration of O2 in the pyrolysis atmosphere was 15%. During spray pyrolysis, SO4... 2- Difficult to be reduced to S 2- Low-valence ions lead to SO4 2- SO4 in cathode materials is difficult to incorporate into the bulk phase. 2- The high enrichment of these elements leads to poor cycle stability of the cathode material.

[0108] In Comparative Example 5, the temperature of the first temperature zone in step (2) is 1400℃, and the volume concentration of O2 in the pyrolysis atmosphere is 15%. The volume percentage of the obtained cathode material at 6t and 1μm is 5%, and SO4 2- The high surface enrichment indicates a high content of micronized powder in the cathode material and a high concentration of free SO4. 2- The high content of [agent] leads to poor cycle stability of the cathode material.

[0109] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A positive electrode material, characterized in that, The cathode material is a single-crystal material, and the general chemical formula of the cathode material is Li. x Ni a Co b M c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, M element includes at least one of Mn or Al, N element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; the free SO4 of the cathode material 2- The content is 100-800 ppm, and SO4 2- The surface enrichment is 10%-70%; and under 6T pressure, the volume ratio of particles smaller than 1μm in the cathode material is 1%-4%, and the particle size Dmin of the cathode material is >0.3μm; Among them, SO4 2- Surface enrichment refers to free SO4 2- Content and SO4 in cathode materials 2- The ratio of total content, wherein 0.5 g of positive electrode material was dissolved in 50 ml of water, sonicated for 5 min, filtered, and the SO4 content of the filtrate was measured by ion chromatography. 2- The content of free SO4 in the cathode material was obtained. 2- The content of.

2. The cathode material according to claim 1, characterized in that, The lattice strain of the cathode material is ≤0.2%.

3. The cathode material according to claim 1, characterized in that, The cathode material further includes a coating layer, which includes at least one element selected from Al, Ti, Zr, Y, Nb, Mg, W, B, Ce, Co, and Mn.

4. The cathode material according to claim 1, characterized in that, The median volumetric particle size D50 of the cathode material is 2.5 μm-5 μm; And / or, the particle size Dmax of the cathode material is <14μm.

5. The positive electrode material according to claim 1, characterized in that, The specific surface area of ​​the positive electrode material is 0.5-1.2 m². 2 / g; And / or, the pH of the positive electrode material satisfies 11.0 ≤ pH ≤ 12.

0.

6. The cathode material according to claim 1, characterized in that, The cathode material comprises grains with the same orientation, and the grain size is 1μm~5μm.

7. A method for preparing a positive electrode material, characterized in that, The preparation method includes: adding H2SO4 to a mixed solution of metal salts containing Ni salt, Co salt, M salt and N salt to obtain a mixed solution; subjecting the mixed solution to pressure atomization treatment and pyrolysis treatment in sequence to obtain a cathode material precursor, wherein the volume content of O2 in the pyrolysis atmosphere is ≤12%; and sintering the cathode material precursor and lithium source to obtain the cathode material. The general formula of the cathode material precursor is Ni. a Co b M c N d O e Wherein, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.35, 0≤d≤0.10, a+b+c+d=1, 1≤e≤1.15, M element includes at least one of Mn and Al, and N element includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; The general chemical formula of the cathode material is Li. x Ni a Co b M c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1; M element, including at least one of Mn and Al; N element, including at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; and the positive electrode material contains free SO4. 2- The content is 100-800 ppm, and SO4 2- The surface enrichment is 10%-70%.

8. The method for preparing the cathode material according to claim 7, characterized in that, In the metal salt mixed solution, the molar ratio of Ni, Co, M and N is (50-98):(0-20):(0-35):(0-0.10), and the molar ratios of Co and M are not both 0. And / or, the Ni salt, M salt, Co salt and N salt each independently include at least one of chloride salt, nitrate salt, oxalate salt and acetate salt; And / or, in the metal salt mixed solution, the concentration of total metal is 100 g / L-500 g / L, wherein the total metal includes Ni, Co, M and N elements; And / or, the pressure of the atomization treatment is 0.4 MPa-0.8 MPa; And / or, the pyrolysis treatment includes a first temperature zone and a second temperature zone, wherein the temperature of the first temperature zone is 1000-1200℃ and the temperature of the second temperature zone is 500-800℃; And / or, in the metal salt mixed solution, based on the total mass of Ni, Co, Mn, and N elements, SO4 2- The content is ≤2400ppm.

9. The method for preparing the cathode material according to claim 8, characterized in that, After atomization, the residence time of the material in the first temperature zone is 2 to 5 seconds.

10. The method for preparing the cathode material according to any one of claims 7 to 9, characterized in that, The sintering temperature is 750-980℃, and the sintering time is 10h-30h; And / or, the sintering atmosphere is an oxygen-containing atmosphere, with O2 accounting for ≥95% by volume; And / or, the molar ratio of lithium in the lithium source to the total metal in the cathode material precursor is 0.98-1.10; wherein, the total metal in the cathode material precursor is the sum of the molar amounts of Ni, Co, M and N.

11. A lithium-ion battery, characterized in that, The lithium-ion battery comprises the cathode material according to any one of claims 1 to 6 or the cathode material prepared by any one of claims 7 to 10.

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