A secondary spherical morphology positive electrode material and a preparation method thereof

Abstract

The application belongs to the field of positive electrode materials, and relates to a secondary spherical morphology positive electrode material and a preparation method thereof. The secondary spherical morphology positive electrode material comprises first secondary spheres formed by agglomeration of first primary particles and second secondary spheres formed by agglomeration of second primary particles, the particle size of the first primary particles is greater than that of the second primary particles, and the secondary spherical morphology positive electrode material is formed by sintering of mixed lithium salt particles and a positive electrode material precursor. The secondary spherical morphology positive electrode material is formed by sintering of two kinds of lithium salt with different particle size distributions in a specific ratio and a precursor, so that the secondary spheres comprise two kinds of secondary spheres formed by agglomeration of primary particles with large particle size and secondary spheres formed by agglomeration of primary particles with small particle size. The special secondary spherical morphology enables the positive electrode material to have high capacity and excellent cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode materials, and relates to a secondary spherical cathode material and its preparation method. Background Technology

[0002] For cathode materials, higher nickel content generally corresponds to higher energy density. With increasing market demands for higher energy density in cathode materials, NCM6-based nickel-based ternary cathode materials have become the mainstream mass-produced ternary cathode materials. NCM8-based and NCA-based high-nickel ternary cathode materials are seen as promising next-generation products for further improving energy density. However, medium- and high-nickel ternary cathode materials inherently suffer from poor cycle performance, and higher nickel content typically leads to even worse cycle performance. Therefore, improving the cycle performance of medium- and high-nickel ternary cathode materials and minimizing capacity loss to maintain high energy density has always been a crucial research direction in the lithium battery industry.

[0003] To address the poor cycling performance of medium- and high-nickel materials, existing technologies typically employ two methods: doping and coating with inactive metal oxides.

[0004] Doping involves adding metal oxides (such as Al2O3, ZrO2, TiO2, etc.) during a single sintering process. However, the doped material is an inactive substance, and to ensure the doping effect, the doping amount is generally greater than 3000 ppm. This will greatly reduce the capacity of the cathode material, and if the doping is uneven or does not enter the cathode material lattice, the expected cycle improvement effect will not be achieved.

[0005] The coating method involves coating an inactive metal oxide (such as Al2O3, ZrO2, W2O3, etc.) after the first firing and then performing a second sintering. However, coating with inactive metal oxides also reduces the capacity, and dry coating has problems of unevenness and easy detachment, while wet coating has problems of poor adhesion and unevenness.

[0006] Therefore, there is an urgent need in this field for a cathode material that combines high capacity and excellent cycle performance, as well as a method for its preparation. Summary of the Invention

[0007] This invention addresses the aforementioned problems in existing technologies by proposing a special secondary spherical cathode material and its preparation method. The secondary spherical cathode material provided by this invention is formed by sintering two lithium salts with different particle size distributions in a specific ratio with a precursor. Therefore, the secondary spheres comprise two types of secondary spheres: first secondary spheres formed by the agglomeration of large-particle primary particles and second secondary spheres formed by the agglomeration of small-particle primary particles. This special secondary spherical morphology enables the cathode material of this invention to possess both high capacity and excellent cycle performance.

[0008] Specifically, one aspect of the present invention provides a method for preparing a special secondary spherical cathode material, wherein the secondary spherical cathode material comprises a first primary particle and a second primary particle, wherein the particle size of the first primary particle is larger than the particle size of the second primary particle, and the secondary spherical cathode material is formed by sintering a mixture of mixed lithium salt particles and a cathode material precursor.

[0009] In one or more embodiments, the mixed lithium salt particles comprise a first lithium salt particle and a second lithium salt particle in a mass ratio of 7.5:2.5 to 8.5:1.5, wherein the first lithium salt particle has a particle size D50 of 15-25 μm and the second lithium salt particle has a particle size D50 of 5-9 μm.

[0010] In one or more embodiments, the secondary spherical cathode material comprises a first secondary sphere formed by the aggregation of the first primary particles and a second secondary sphere formed by the aggregation of the second primary particles.

[0011] In one or more embodiments, the mass ratio of the first lithium salt particles to the second lithium salt particles in the mixed lithium salt is from 7.8:2.2 to 8.2:1.8, for example 8:2.

[0012] In one or more embodiments, the particle size D50 of the first lithium salt particles is 17-20 μm, preferably 17-18 μm.

[0013] In one or more embodiments, the particle size D50 of the second lithium salt particles is 6-7 μm, preferably 6-6.5 μm.

[0014] In one or more embodiments, the particle size distribution Span value of the first lithium salt particles is ≤0.5.

[0015] In one or more embodiments, the particle size distribution Span value of the second lithium salt particles is ≤0.8.

[0016] In one or more embodiments, the difference between the particle size D50 of the first lithium salt particle and the particle size D50 of the second lithium salt particle is 10-12 μm.

[0017] In one or more embodiments, the lithium salt is selected from one or both of lithium hydroxide and lithium carbonate.

[0018] In one or more embodiments, the cathode material precursor is nickel cobalt manganese hydroxide, nickel cobalt aluminum hydroxide, or nickel cobalt manganese aluminum hydroxide.

[0019] In one or more embodiments, the particle size D50 of the cathode material precursor is 3-15 μm.

[0020] In one or more embodiments, the secondary spherical cathode material is a nickel-cobalt-manganese ternary cathode material, a nickel-cobalt-aluminum ternary cathode material, or a nickel-cobalt-manganese-aluminum quaternary cathode material.

[0021] In one or more embodiments, the secondary spherical cathode material is a medium-nickel cathode material or a high-nickel cathode material. In the medium-nickel cathode material, the amount of nickel element accounts for ≥60% and <80% of the total amount of nickel and M element. In the high-nickel cathode material, the amount of nickel element accounts for ≥80% and preferably 80%-96% of the total amount of nickel and M element. The M element is two or three of Co, Mn and Al.

[0022] In one or more embodiments, the molar ratio of the cathode material precursor to the mixed lithium salt particles is 1:(1-1.1).

[0023] Another aspect of the present invention provides a method for preparing a secondary spherical cathode material as described in any embodiment herein, the method comprising the following steps:

[0024] (1) The first lithium salt particles, the second lithium salt particles, the cathode material precursor and the optional dopant are mixed evenly to obtain a first mixture.

[0025] (2) The first mixture is sintered once, and the sintered product is crushed to obtain the first powder;

[0026] (3) The first powder is sintered twice to obtain the secondary spherical cathode material; or, the first powder is mixed evenly with a coating agent to obtain a second mixture, and the second mixture is sintered twice to obtain the secondary spherical cathode material.

[0027] In one or more embodiments, the first lithium salt particles and the second lithium salt particles are obtained by crushing and sieving lithium salt raw material particles with a particle size D50 ≥ 200 μm. The crushing is preferably carried out using an air jet mill, and the preferred particle size D50 of the lithium salt raw material particles is 200-300 μm.

[0028] In one or more embodiments, the temperature of the first sintering is 600-1000°C.

[0029] In one or more embodiments, the sintering time is 8-15 hours.

[0030] In one or more embodiments, the particle size D50 of the first powder is 3-15 μm.

[0031] In one or more embodiments, the dopant is a compound containing element A, wherein element A is selected from one or more of Li, Zr, Ti, Al, Mg, Co, Mn, Sr, Mo, Ne, B and F, and the mass of element A in the dopant preferably accounts for 0-1000 ppm of the mass of the first powder.

[0032] In one or more embodiments, the coating agent is a compound containing element B, wherein element B is selected from one or more of Li, Zr, Ti, Al, Mg, Co, Mn, Sr, Mo, Ne, B and F, and the mass of element B in the coating agent preferably accounts for 0-5000 ppm of the mass of the secondary spherical cathode material.

[0033] In one or more embodiments, the temperature of the secondary sintering is 100-700°C.

[0034] In one or more embodiments, the secondary sintering time is 2-15 hours.

[0035] In one or more embodiments, the secondary spherical cathode material is a medium-nickel cathode material; the primary sintering temperature for preparing the medium-nickel cathode material is 700-1000℃;

[0036] In one or more embodiments, the first mixture may or may not contain a dopant.

[0037] In one or more embodiments, the residual alkali content in the first powder of the nickel cathode material is low and does not need to be removed by water washing. Therefore, the first powder obtained in step (2) is directly carried out in step (3).

[0038] In one or more embodiments, the secondary spherical cathode material is a high-nickel cathode material; the primary sintering temperature for preparing the high-nickel cathode material is 600-800℃;

[0039] In one or more embodiments, the first mixture may or may not contain a dopant.

[0040] In one or more embodiments, since the residual alkali content in the first powder of the high nickel cathode material is high, it is easy to cause serious gas generation in the subsequent process. It needs to be removed by water washing. Therefore, the first powder obtained in step (2) is washed and dried before step (3).

[0041] In one or more embodiments, the water-to-material mass ratio of the water washing is (0.5-2):1.

[0042] In one or more embodiments, the washing time is 1-10 minutes.

[0043] In one or more embodiments, the water washing speed is 100-500 Hz.

[0044] In one or more embodiments, the drying is vacuum drying.

[0045] The secondary spherical cathode material of the present invention can be prepared by the method described in any embodiment of the present invention.

[0046] Another aspect of the present invention provides a positive electrode sheet containing a secondary spherical positive electrode material as described in any embodiment of the present invention.

[0047] Another aspect of the present invention provides a lithium-ion battery comprising a positive electrode as described in any embodiment herein. Attached Figure Description

[0048] Figure 1 This is a particle size distribution diagram of lithium hydroxide II with a conventional particle size distribution.

[0049] Figure 2 The particle size distribution diagram of the mixed lithium hydroxide used in Example 1 (lithium hydroxide III and lithium hydroxide IV were mixed at a mass ratio of 8:2).

[0050] Figure 3 This is a scanning electron microscope image of the positive electrode material prepared in Example 1.

[0051] Figure 4 This is a scanning electron microscope image of the cathode material prepared in Comparative Example 1.

[0052] Figure 5 This is a scanning electron microscope image of the cathode material prepared in Comparative Example 2.

[0053] Figure 6 This is a scanning electron microscope image of the cathode material prepared in Comparative Example 3.

[0054] Figure 7 This is a scanning electron microscope image of the cathode material prepared in Comparative Example 4.

[0055] Figure 8 This is a scanning electron microscope image of the cathode material prepared in Comparative Example 5.

[0056] Figure 9 This is a scanning electron microscope image of the cathode material prepared in Comparative Example 6.

[0057] Figure 10 This is a scanning electron microscope image of the cathode material prepared in Comparative Example 7.

[0058] Figure 11 This is a scanning electron microscope image of the positive electrode material prepared in Example 2.

[0059] Figure 12 A comparison chart of the discharge specific capacity of lithium-ion batteries made using the cathode materials obtained in Example 1 and Comparative Examples 1-4.

[0060] Figure 13 A comparison chart of the discharge specific capacity of lithium-ion batteries made using the cathode materials obtained in Examples 2-4 and Comparative Examples 5-7.

[0061] Figure 14 A comparison chart showing the cycle retention rates of lithium-ion batteries made using the cathode materials obtained in Example 1 and Comparative Examples 1-4.

[0062] Figure 15 Comparison chart of cycle retention rates of lithium-ion batteries made using the cathode materials obtained in Examples 2-4 and Comparative Examples 5-7. Detailed Implementation

[0063] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used herein are explained and defined in general terms below. Unless otherwise specified, all technical and scientific terms used herein have the common meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0064] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0065] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0066] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0067] Unless otherwise specified, percentages refer to mass percentages and proportions refer to mass ratios in this article.

[0068] In this article, the sum of the percentages of all components in the composition is 100%.

[0069] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope of this invention.

[0070] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0071] The purpose of this invention is to provide a high-cycle cathode material with a special morphology of secondary spheres by controlling the particle size distribution of lithium salts (lithium hydroxide and / or lithium carbonate), thereby improving the cycle performance of the cathode material while maintaining high capacity. Compared with modification methods using doping or coating with metal oxides, the cathode material of this invention has a higher capacity, and its cycle performance is even better due to the mixture of secondary spheres with different morphologies at the microscopic level. In this invention, the particle size of the first primary particles of the cathode material is larger than that of the second primary particles, which can be understood as the particle size D50 of the first primary particles being larger than that of the second primary particles. This is due to the use of two lithium salt particles with different particle sizes.

[0072] Lithium salts of different particle sizes

[0073] In this invention, first lithium salt particles and second lithium salt particles can be prepared using lithium salt raw material particles with a particle size D50 ≥ 200 μm. In some embodiments, the particle size D50 of the lithium salt raw material particles can be 200-300 μm, for example, D50 of 200 μm, 220 μm, 229.7 μm, 240 μm, 260 μm, 280 μm, and 300 μm. The first and second lithium salt particles can be obtained by pulverizing and sieving the lithium salt raw material particles. In some embodiments, an air jet mill is used for pulverization.

[0074] In some implementations, the mass ratio of the first lithium salt particles to the second lithium salt particles in the mixed lithium salt is from 7.8:2.2 to 8.2:1.8, for example 7.9:2.1, 8:2, or 8.1:1.9. This is beneficial for improving the cycle performance of the cathode material while maintaining high capacity.

[0075] The present invention further discovers that the best overall performance of the prepared cathode material is achieved when the first lithium salt particle (D50 = 15-25 μm, preferably 17-20 μm, Span ≤ 0.50) and the second lithium salt particle (D50 = 5-9 μm, preferably 6-7 μm, Span ≤ 0.80) have a narrow particle size distribution, and the difference in D50 between the first and second lithium salt particles is 10-12 μm. This also results in the formation of two distinct secondary spherical morphologies. If the difference in D50 between the two lithium salt particles is less than 10 μm, during secondary calcination, the melting and diffusion of the lithium salt will cause the number of lithium salt particles near the primary particles to become more uniform, resulting in insignificant differences in the primary particle size of the cathode material.

[0076] In some embodiments, the particle size D50 of the first lithium salt particles is preferably 17-20 μm, more preferably 17-18 μm, for example 17.1 μm, 17.2 μm, 17.3 μm, 17.4 μm, 17.5 μm, 17.6 μm, 17.7 μm, 17.8 μm, and 17.9 μm. This invention has found that if the particle size D50 of the first lithium salt particles is greater than 20 μm, it is not conducive to uniformly mixing the first and second lithium salt particles, and thus not conducive to improving the performance of the cathode material.

[0077] In some embodiments, the particle size D50 of the second lithium salt particles is preferably 6-7 μm, more preferably 6-6.5 μm, such as 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm.

[0078] In some embodiments, the particle size distribution Span value of the first lithium salt particles is preferably ≤0.5, for example, Span values ​​of 0.1, 0.2, 0.3, 0.4, and 0.5. This is beneficial for improving the particle size distribution of the first lithium salt particles, thereby improving the secondary spherical morphology and cycle performance of the cathode material, while maintaining high capacity.

[0079] In some embodiments, the particle size distribution Span value of the second lithium salt particles is preferably ≤0.8, for example, Span values ​​of 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8. This is beneficial for improving the particle size distribution of the second lithium salt particles, thereby improving the secondary spherical morphology and cycle performance of the cathode material, while maintaining high capacity.

[0080] In some embodiments, the difference between the particle size D50 of the first lithium salt particles and the particle size D50 of the second lithium salt particles is preferably 10-12 μm, for example, 10.0 μm, 10.1 μm, 10.2 μm, 10.3 μm, 10.4 μm, 10.5 μm, 10.6 μm, 10.7 μm, 10.8 μm, 10.9 μm, 11.0 μm, 11.1 μm, 11.2 μm, 11.3 μm, 11.4 μm, 11.5 μm, 11.6 μm, 11.7 μm, 11.8 μm, 11.9 μm, and 12.0 μm. This is beneficial for controlling the particle size difference between the first and second lithium salts, thereby improving the secondary spherical morphology and cycle performance of the cathode material while maintaining high capacity.

[0081] In some embodiments, the lithium salt is selected from one or both of lithium hydroxide and lithium carbonate, for example, both the first and second lithium salts are lithium hydroxide, both the first and second lithium salts are lithium carbonate, the first lithium salt is lithium hydroxide and the second lithium salt is lithium carbonate, and the first lithium salt is lithium carbonate and the second lithium salt is lithium hydroxide. In some embodiments, the lithium salt is lithium hydroxide.

[0082] Secondary spherical cathode material

[0083] The secondary spherical cathode material of the present invention comprises a first secondary sphere formed by the agglomeration of a first primary particle and a second secondary sphere formed by the agglomeration of a second primary particle, wherein the particle size of the first primary particle is larger than that of the second primary particle. The secondary spherical cathode material of the present invention is formed by sintering a mixture of mixed lithium salt particles and a cathode material precursor; the mixed lithium salt particles include a first lithium salt particle and a second lithium salt particle with a mass ratio of 7.5:2.5 to 8.5:1.5, wherein the particle size D50 of the first lithium salt particle is 15-25 μm, and the particle size D50 of the second lithium salt particle is 5-9 μm.

[0084] This invention reveals that when lithium salts of two particle sizes with a specific mass ratio are mixed with a precursor and then sintered, when the lithium hydroxide particle size distribution is narrow, large-diameter lithium hydroxide and small-diameter lithium hydroxide particles are respectively attached to the precursor of the cathode material. The precursor with attached large-diameter lithium hydroxide has a higher lithium content, therefore, after high-temperature melting, the lithium content near the primary particles of the secondary spheres is higher, resulting in larger primary particles. The prepared cathode material exhibits high capacity and low cycle performance, i.e., capacity-type particles. Conversely, the precursor with attached small-diameter lithium hydroxide has a lower lithium content, resulting in smaller primary particles. The prepared cathode material exhibits low capacity and high cycle performance, i.e., cycle-type particles. Therefore, the two types of secondary sphere particles in the cathode material prepared by using lithium salts of different particle sizes can coordinate with each other, achieving the effect of improved cycle performance with less or virtually no capacity loss compared to doping with inactive metal oxides, while maintaining the same mass of active material. In summary, by controlling the particle size distribution of lithium salts, the lithium content distribution during sintering can be controlled, thereby changing the size of the primary particles in the secondary spheres of the cathode material and ultimately controlling the electrochemical performance of the battery.

[0085] In some implementations, the cathode material precursor is nickel cobalt manganese hydroxide, nickel cobalt aluminum hydroxide, or nickel cobalt manganese aluminum hydroxide.

[0086] In some implementations, the secondary spherical cathode material is a nickel-cobalt-manganese ternary cathode material, a nickel-cobalt-aluminum ternary cathode material, or a nickel-cobalt-manganese-aluminum quaternary cathode material.

[0087] In some implementations, the precursor for preparing the cathode material has the chemical formula Ni. x M y (OH)₂, where x + y = 1. The M element is two or three of Co, Mn, and Al, for example, a combination of Co and Mn, a combination of Mn and Al, a combination of Co and Al, or a combination of Co, Mn, and Al. The M element plays a role in stabilizing the material structure within the cathode material.

[0088] The secondary spherical cathode material is a medium-nickel cathode material or a high-nickel cathode material. In the medium-nickel cathode material, the amount of nickel in the total amount of nickel and M elements is ≥60% and <80%, for example, 60%, 62%, 64%, 66%, 68%, 70%, 72%, 74%, 76%, 78%, and 79%. In the high-nickel cathode material, the amount of nickel in the total amount of nickel and M elements is ≥80%, preferably 80%-96%, for example, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, and 96%.

[0089] In some implementations, the particle size D50 of the cathode material precursor can be 3-15 μm, for example 13.0 μm, 13.3 μm, 13.5 μm, 13.8 μm, 14.0 μm, 14.3 μm, 15 μm.

[0090] In some implementations, the molar ratio of the cathode material precursor to the mixed lithium salt particles is preferably 1:(1-1.1), such as 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09, and 1:1.1.

[0091] In some embodiments, the method for producing the medium-nickel or high-nickel secondary spherical cathode material of the present invention includes the following steps:

[0092] (1) Mix the first lithium salt particles, the second lithium salt particles, the cathode material precursor and the optional dopant evenly to obtain the first mixture material;

[0093] (2) The first mixture is sintered once, and the sintered product is crushed to obtain the first powder;

[0094] (3) The first powder is sintered twice to obtain a secondary spherical cathode material; or, the first powder is mixed evenly with a coating agent to obtain a second mixture, and the second mixture is sintered twice to obtain a secondary spherical cathode material.

[0095] In some embodiments, the dopant optionally added in step (1) is a compound containing element A, which is one or more of Li, Zr, Ti, Al, Mg, Co, Mn, Sr, Mo, Ne, B, and F. The mass of element A can be 0-1000 ppm of the mass of the first mixture, for example, 0 ppm, 100 ppm, 200 ppm, 400 ppm, 600 ppm, 800 ppm, or 1000 ppm.

[0096] In some implementations, the sintering temperature in step (2) is 600-1000℃, for example 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃.

[0097] In some implementations, the sintering time in step (2) is 8-15 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, or 15 hours.

[0098] In some embodiments, the particle size D50 of the first powder obtained after sintering is 3-15 μm, for example 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm.

[0099] In some embodiments, the coating agent in step (3) is a compound containing element B, wherein element B is selected from one or more of Li, Zr, Ti, Al, Mg, Co, Mn, Sr, Mo, Ne, B, and F. The mass of element B in the coating agent can be 0-5000 ppm of the mass of the secondary spherical cathode material, for example, 0 ppm, 100 ppm, 500 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, and 5000 ppm.

[0100] In some implementations, the secondary sintering temperature in step (3) is 100-700℃, for example 100℃, 200℃, 300℃, 400℃, 500℃, 580℃, 600℃, 700℃.

[0101] In some implementations, the secondary sintering time in step (3) is 2-15 hours, for example, 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, or 15 hours.

[0102] In some implementations, when preparing the nickel cathode material, the first powder obtained in step (2) is directly used in step (3).

[0103] In some implementations, when preparing high-nickel cathode materials, the first powder obtained in step (2) is washed with water and dried before step (3).

[0104] In some implementations, when preparing high-nickel cathode materials, the water-to-material mass ratio during washing is (0.5-2):1, for example, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1, or 2:1.

[0105] In some implementations, the washing time is 1-10 minutes, for example, 1 minute, 3 minutes, 5 minutes, 7 minutes, 9 minutes, or 10 minutes.

[0106] In some implementations, the water washing speed is 100-500 Hz when preparing high-nickel cathode materials, for example, 100 Hz, 150 Hz, 200 Hz, 250 Hz, 300 Hz, 350 Hz, 400 Hz, 450 Hz, and 500 Hz.

[0107] In some implementations, the drying process for preparing high-nickel cathode materials involves one or more methods, namely vacuum drying and atmospheric pressure drying. The vacuum level during vacuum drying is ≥0.06 MPa.

[0108] This invention improves the cycle performance of the cathode material by controlling the lithium salt particle size distribution to form two secondary sphere morphologies: a first secondary sphere formed by the aggregation of a first primary particle and a second secondary sphere formed by the aggregation of a second primary particle. Compared with cathode materials doped or coated with metal oxides, the cathode material of this invention has a higher discharge specific capacity, and its electrode performance is more stable due to the mixing of secondary spheres with different morphologies.

[0109] Lithium-ion batteries

[0110] A lithium-ion battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte. The lithium-ion battery of this invention is characterized by a positive electrode comprising a high-nickel positive electrode material with a special secondary spherical morphology as described in this invention. The positive electrode, negative electrode, and separator can be stacked according to design requirements (e.g., Z-shaped stacking or wound stacking), the cell is installed in a casing, and then the electrolyte is injected. After formation, aging, and capacity testing, a lithium-ion battery is manufactured.

[0111] The positive electrode sheet includes a positive current collector and a positive electrode material layer formed on the surface of the positive current collector. The positive electrode material layer includes a positive electrode material, a conductive agent, and a binder. The positive electrode material layer is obtained by coating a positive electrode slurry containing the positive electrode material, conductive agent, binder, and solvent onto the positive current collector, followed by rolling, die-cutting, and drying. In this invention, the positive current collector is aluminum foil. The solvent for the positive electrode slurry is N-methylpyrrolidone (NMP). The positive electrode material in the positive electrode sheet of this invention is the high-nickel positive electrode material of this invention. The conductive agent for the positive electrode is conductive carbon black (SP), and the binder is polyvinylidene fluoride (PVDF). When preparing the positive electrode sheet, the positive electrode material, conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed and ground evenly in a mortar at a mass ratio of 6:3:1-9:0.5:0.5 (e.g., 8:1:1). During the grinding process, an appropriate amount of NMP is added dropwise to adjust the viscosity of the slurry. After thorough grinding, the slurry is evenly coated onto the current collector aluminum foil and dried at 80℃ for 1-3 days, for example, 2 days. After the electrode is dried, the electrode is cut into circular electrode sheets with a diameter of 15-25mm using a punching machine, for example, 15mm. The mass of a single electrode sheet is weighed using an electronic balance and placed in a glove box (H2O content <1ppm, oxygen content <0.2ppm) for later use.

[0112] The negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on the surface of the negative current collector. The negative current collector can be copper foil. The negative electrode material layer includes negative electrode material, a conductive agent, and a binder. The negative electrode material layer is obtained by coating a negative electrode slurry containing negative electrode material, conductive agent, binder, and solvent onto the negative current collector, followed by rolling, die-cutting, and drying. The solvent for the negative electrode slurry can be water. The negative electrode material can be lithium metal, mesophase carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, or spinel-structured lithiated TiO2-Li4Ti5O. 12 The negative electrode may be one or more of the following: Li-Al alloy. The negative electrode conductive agent may be one or more selected from conductive carbon black (SP), acetylene black, carbon nanotubes, carbon nanowires, carbon microspheres, carbon fibers, and graphene. The negative electrode binder may be one or more selected from polyvinylidene fluoride, polytetrafluoroethylene, acrylonitrile copolymer, polybutylene acrylate, polyacrylonitrile, and styrene-butadiene rubber (SBR). The mass ratio of the components in the negative electrode material layer can be conventional. The negative electrode sheet may be a lithium sheet.

[0113] The separator can be a polymer porous separator, an inorganic porous separator, or a polymer-inorganic composite porous separator. Polymer porous separators include single-layer polymer porous separators and multi-layer polymer porous separators. The positive electrode, negative electrode, and separator are assembled according to design requirements, such as stacking or winding them into a casing. After drying, electrolyte injection, encapsulation, settling, formation, and sorting, a lithium-ion battery can be obtained. The form of the lithium-ion battery of this invention is not particularly limited and can be a button cell, cylindrical lithium-ion battery, pouch lithium-ion battery, or aluminum-cased lithium-ion battery, etc.

[0114] Lithium-ion battery electrolytes contain organic solvents and lithium salts. Commonly used organic solvents in electrolytes are carbonate solvents. Suitable carbonate solvents include, but are not limited to, one or more selected from ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), preferably two or more. Preferably, the carbonate solvent contains at least one cyclic carbonate and at least two linear carbonates. Examples of cyclic carbonates include EC, PC, and butenyl carbonate. Examples of linear carbonates include DMC, DEC, and EMC. The mass ratio of cyclic carbonates to linear carbonates can be 1:1:4 to 2:1:1, for example, 1:1:1. The lithium salt in the electrolyte of this invention can be a commonly used lithium salt in the art, including but not limited to lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium fluoride (LiF), lithium trifluoromethanesulfonate (LiCF3SO3), etc. In some embodiments, the lithium salt is LiPF6. The concentration of the lithium salt in the electrolyte can be 0.5-2 mol / L, for example, 1 mol / L.

[0115] The present invention has the following beneficial effects:

[0116] 1. This invention proposes to prepare cathode materials using mixed lithium salts of two particle sizes. After melting and diffusion, due to the different lithium hydroxide content at the location of the secondary spheres in the cathode material, the primary particles of different secondary spheres in the cathode material exhibit two different morphologies.

[0117] 2. In the special secondary spherical morphology, the larger primary particles are capacity-type and the smaller primary particles are cycle-type. The two types of particles cooperate with each other. Under the same active material mass, compared with doped inactive metal oxides, the cathode material with the special secondary spherical morphology has significantly improved cycle performance and achieved the effect of small or almost no capacity loss.

[0118] 3. The method for preparing the cathode material proposed in this invention does not require the addition of metal oxides, thereby increasing the proportion of active material in the cathode material and achieving a higher specific capacitance.

[0119] 4. By adjusting the particle size distribution of lithium hydroxide to be narrower, the unstable structure of the cathode material due to uneven doping can be avoided.

[0120] The present invention will be described below by way of specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the invention. The methods, reagents, and materials used in the embodiments and comparative examples are conventional methods, reagents, and materials in the art, unless otherwise stated. The starting material compounds in the embodiments and comparative examples are all commercially available.

[0121] In this invention, the particle size Dmin, D10, D50, D90, Dmax and particle size distribution Span value of the material are determined using a laser particle size analyzer.

[0122] Example of lithium hydroxide preparation

[0123] (1) Lithium hydroxide I

[0124] Lithium hydroxide I has the particle size distribution shown in Table 1. Lithium hydroxide I is available commercially.

[0125] Table 1: Particle size distribution of lithium hydroxide I

[0126] 0.6 9.97 229.7 453.3 707.6

[0127] (2) Preparation of lithium hydroxide II with conventional particle size distribution

[0128] Lithium hydroxide I was pulverized using an air jet mill, with pulverization parameters shown in Table 2, to obtain lithium hydroxide II, the particle size distribution of which is shown in Table 3. Figure 1 As shown.

[0129] Table 2: Pulverization parameters for preparing lithium hydroxide II with conventional particle size distribution

[0130] 35 50 0.7 20

[0131] Table 3: Particle size distribution of lithium hydroxide II

[0132] 0.5 2.1 9.6 32.0 58.8 3.1

[0133] (3) Preparation of large-particle lithium hydroxide III

[0134] Lithium hydroxide I was pulverized using an air jet mill, with pulverization parameters shown in Table 4, to obtain pulverized lithium hydroxide A.

[0135] Table 4: Pulverization parameters for preparing pulverized lithium hydroxide A

[0136] 23 50 0.7 50

[0137] The grading frequency is reduced to obtain materials with a larger D50; the induced draft fan frequency is increased to reduce the amount of micro powder.

[0138] After crushing, the crushed lithium hydroxide A is sieved through an 1800-mesh sieve (pore size 10μm) to further separate lithium hydroxide particles of different sizes. The material remaining on the sieve is the large-particle lithium hydroxide, denoted as lithium hydroxide III, and its particle size distribution is shown in Table 5.

[0139] Table 5: Particle size distribution of large-particle lithium hydroxide III

[0140] 8.7 14.2 17.6 20.9 32.6 0.4

[0141] (4) Preparation of small-particle lithium hydroxide IV

[0142] Lithium hydroxide I was pulverized using an air jet mill, with pulverization parameters shown in Table 6, to obtain pulverized lithium hydroxide B.

[0143] Table 6: Pulverization parameters for preparing pulverized lithium hydroxide B

[0144]

[0145]

[0146] Increasing the grading frequency yields materials with smaller D50; decreasing the induced draft fan frequency increases the number of small particles.

[0147] After crushing, the crushed lithium hydroxide B is sieved through a 900-mesh sieve (pore size of 20μm) to further separate lithium hydroxide particles of different sizes. The material passing through the sieve is the small-particle lithium hydroxide, denoted as lithium hydroxide IV, and its particle size distribution is shown in Table 7.

[0148] Table 7: Particle size distribution of small-particle lithium hydroxide B and lithium hydroxide IV

[0149] B 2.8 4.6 7.9 15.6 26.5 1.4 Ⅳ 2.7 4.3 6.1 8.1 14.6 0.6

[0150] (5) Preparation of ultra-large particle lithium hydroxide V

[0151] Lithium hydroxide I was pulverized using an air jet mill, with pulverization parameters shown in Table 8, to obtain pulverized lithium hydroxide C.

[0152] Table 8: Pulverization parameters for preparing pulverized lithium hydroxide C

[0153] 18 50.0 0.7 50

[0154] The grading frequency is reduced to obtain materials with a larger D50; the induced draft fan frequency is reduced to increase the number of small particles.

[0155] After crushing, the crushed lithium hydroxide C is sieved through an 1800-mesh sieve (pore size 10μm) to further separate lithium hydroxide particles of different sizes. The material remaining on the sieve is the ultra-large lithium hydroxide particles, denoted as lithium hydroxide V. Its particle size distribution is shown in Table 9.

[0156] Table 9: Particle size distribution of lithium hydroxide C and lithium hydroxide V

[0157] C 1.5 5.7 19.7 45.0 71.8 2.0 Ⅴ 9.8 16.2 23.4 30.4 44.9 0.6

[0158] (6) Preparation of lithium hydroxide VI

[0159] The pulverized lithium hydroxide II was sieved through an 1800-mesh sieve (10 μm aperture) to further separate lithium hydroxide particles of different sizes. The material remaining on the sieve is the desired lithium hydroxide, denoted as lithium hydroxide VI. Its particle size distribution is shown in Table 10.

[0160] Table 10: Particle size distribution of lithium hydroxide VI

[0161] 4.1 7.5 11.1 15.5 21.6 0.7

[0162] (7) Preparation of large-particle lithium hydroxide VII

[0163] Lithium hydroxide I was pulverized using an air jet mill, and the pulverization parameters are shown in Table 11, to obtain pulverized lithium hydroxide D.

[0164] Table 11: Pulverization parameters for preparing pulverized lithium hydroxide D

[0165] 21 50.0 0.7 50

[0166] The grading frequency is reduced to obtain materials with a larger D50; the induced draft fan frequency is increased to reduce the number of small particles.

[0167] After crushing, the crushed lithium hydroxide D is sieved through an 1800-mesh sieve (pore size 10μm) to further separate lithium hydroxide particles of different sizes. The material remaining on the sieve is the ultra-large lithium hydroxide particles, denoted as lithium hydroxide VII, and its particle size distribution is shown in Table 12.

[0168] Table 12: Particle size distribution of lithium hydroxide VII

[0169] 8.9 16.2 18.7 24.3 38.0 0.4

[0170] (8) Preparation of small-particle lithium hydroxide VIII

[0171] Lithium hydroxide I was pulverized using an air jet mill, and the pulverization parameters are shown in Table 13, to obtain pulverized lithium hydroxide E.

[0172] Table 13: Pulverization parameters for preparing pulverized lithium hydroxide D

[0173] 52 50 0.7 10

[0174] The higher grading frequency results in materials with smaller D50; the lower induced draft fan frequency increases the number of small particles.

[0175] After crushing, the crushed lithium hydroxide E is sieved through a 900-mesh sieve (pore size 20μm) to further separate lithium hydroxide particles of different sizes. The material passing through the sieve is the small-particle lithium hydroxide, denoted as lithium hydroxide VIII, and its particle size distribution is shown in Table 14.

[0176] Table 14: Particle size distribution of lithium hydroxide VIII

[0177] 2.8 5.4 6.8 10.3 17.4 0.7

[0178] Example 1

[0179] This embodiment prepares a high-nickel cathode material:

[0180] (1) Lithium hydroxide III and lithium hydroxide IV were mixed at a mass ratio of 8:2 to obtain mixed lithium hydroxide. The particle size distribution of the mixed lithium hydroxide is shown in the figure. Figure 2 ;

[0181] (2) The precursor Ni with a molar ratio of 1:1.05 0.88 Co 0.10 Al 0.02 (OH)2 and lithium hydroxide from step (1) were mixed using a high-speed mixer; sintered at 700℃ for 10 h, and the resulting powder was pulverized and designated as powder I-a, precursor D. 50 =13.5μm, D after calcination and pulverization 50 =13.0μm;

[0182] (3) Wash the powder I-a obtained in step (2) with pure water for 3 minutes, with a water-to-material mass ratio of 0.8:1 and a rotation speed of 150 Hz. After washing, dry it in a vacuum oven with a vacuum degree ≥0.06 MPa to obtain powder II-a;

[0183] (4) The powder II-a obtained in step (3) is sintered at 580℃ for 8 hours to obtain powder III-a, which is the high-nickel cathode material. Its microstructure is as follows: Figure 3 As shown.

[0184] Comparative Example 1

[0185] This comparative example prepares a high-nickel cathode material:

[0186] (1) Ni precursor 0.88 Co 0.10 Al 0.02 (OH)₂, lithium hydroxide II, and TiO₂ are mixed using a high-speed mixer to obtain a mixture, wherein Ni 0.88 Co 0.10 Al 0.02 The molar ratio of (OH)₂ to lithium hydroxide is 1:1.05. The molar relationship between the amount of TiO₂ added and the amount of transition metal is as follows: Timol / M mol =3000ppm (M is transition metals Ni, Co, and Al, precursor D) 50 =13.5μm);

[0187] (2) The mixture from step (1) is sintered at 700℃ for 10 hours, and then pulverized to obtain powder Ib, D. 50 =13.0μm;

[0188] (3) Wash the powder Ib obtained in step (2) with pure water for 3 minutes, where the water-to-powder mass ratio is 0.8:1 and the rotation speed is 150 Hz. After washing, dry it in a vacuum oven with a vacuum degree ≥0.06 MPa to obtain powder II-b;

[0189] (4) The powder II-b obtained in step (3) is mixed with the coating agent CeO2 and sintered at 580℃ for 8 hours to obtain powder III-b, which is the high-nickel cathode material. Its microstructure is as follows: Figure 4 As shown. The mass ratio of CeO2 to powder II-b is 500 ppm, i.e., m(CeO2) / m(powder II-b) = 500 ppm.

[0190] Comparative Example 2

[0191] This comparative example prepares a high-nickel cathode material:

[0192] (1) Lithium hydroxide III and lithium hydroxide IV are mixed in a mass ratio of 9:1 to obtain mixed lithium hydroxide;

[0193] (2) Ni with a molar ratio of 1:1.05 0.88 Co 0.10 Al 0.02 The (OH)2 precursor and the mixed lithium hydroxide obtained in step (1) were mixed using a high-speed mixer and sintered at 700°C for 10 hours. The resulting powder was pulverized and labeled as powder I-c, and precursor D was pulverized as powder D. 50 =13.5μm, D after calcination and pulverization 50 =13.0μm;

[0194] Steps (3) and (4) are the same as in Example 1, yielding powder III-c, which is the high-nickel cathode material, with the following microstructure: Figure 5 As shown.

[0195] Comparative Example 3

[0196] This comparative example prepares a high-nickel cathode material:

[0197] (1) Lithium hydroxide III and lithium hydroxide IV are mixed in a mass ratio of 7:3 to obtain mixed lithium hydroxide;

[0198] (2) Ni with a molar ratio of 1:1.05 0.88 Co 0.10 Al 0.02 The (OH)2 precursor and the mixed lithium hydroxide obtained in step (1) were mixed using a high-speed mixer and sintered at 700°C for 10 hours. The resulting powder was pulverized and labeled as powder I-d, and precursor D was pulverized as powder D. 50 =13.5μm, D after calcination and pulverization 50 =13.0μm;

[0199] Steps (3) and (4) are the same as in Example 1, yielding powder III-d, which is the high-nickel cathode material, with the following microstructure: Figure 6 As shown.

[0200] Comparative Example 4

[0201] This comparative example prepares a high-nickel cathode material:

[0202] (1) Ni with a molar ratio of 1:1.05 0.88 Co 0.10 Al 0.02 (OH)₂ precursor and lithium hydroxide II were mixed using a high-speed mixer, sintered at 700℃ for 10 h, and pulverized and labeled as powder I-e, precursor D. 50 =13.5μm, D after calcination and pulverization 50 =13.0μm;

[0203] (2) Wash powder I-e with pure water for 3 minutes, where the water-to-material mass ratio is 0.8:1 and the rotation speed is 150Hz. After washing, dry it in a vacuum oven with a vacuum degree ≥0.06MPa to obtain powder II-e.

[0204] (3) The powder II-e obtained in step (2) is sintered at 580℃ for 8 hours to obtain powder III-e, which is the high-nickel cathode material. Its microstructure is as follows: Figure 7 As shown.

[0205] Comparative Example 5

[0206] This comparative example prepares a high-nickel cathode material:

[0207] (1) Lithium hydroxide V and lithium hydroxide IV are mixed at a mass ratio of 8:2 to obtain mixed lithium hydroxide;

[0208] (2) The precursor Ni with a molar ratio of 1:1.05 0.88 Co 0.10 Al 0.02 (OH)2 and lithium hydroxide from step (1) were mixed using a high-speed mixer; sintered at 700℃ for 10 h, and the resulting powder was pulverized and designated as powder I-f, precursor D. 50=13.5μm, D after calcination and pulverization 50 =13.0μm;

[0209] (3) Wash the powder I-f obtained in step (2) with pure water for 3 minutes, with a water-to-material mass ratio of 0.8:1 and a rotation speed of 150 Hz. After washing, dry it in a vacuum oven with a vacuum degree ≥0.06 MPa to obtain powder II-f;

[0210] (4) The powder II-f obtained in step (3) is sintered at 580℃ for 8 hours to obtain powder III-f, which is the high-nickel cathode material. Its microstructure is as follows: Figure 8 As shown.

[0211] Comparative Example 6

[0212] This comparative example prepares a high-nickel cathode material:

[0213] (1) Lithium hydroxide III and lithium hydroxide VI are mixed at a mass ratio of 8:2 to obtain mixed lithium hydroxide;

[0214] (2) The precursor Ni with a molar ratio of 1:1.05 0.88 Co 0.10 Al 0.02 (OH)2 and lithium hydroxide from step (1) were mixed using a high-speed mixer; sintered at 700℃ for 10 h, and the resulting powder was recorded as powder I-g, precursor D. 50 =13.5μm, D after calcination and pulverization 50 =13.0μm;

[0215] (3) Wash the powder I-g obtained in step (2) with pure water for 3 min, with a water-to-material mass ratio of 0.8:1 and a rotation speed of 150 Hz. After washing, dry it in a vacuum oven with a vacuum degree ≥0.06 MPa to obtain powder II-g;

[0216] (4) The powder II-g obtained in step (3) is sintered at 580℃ for 8 hours to obtain powder III-g, which is the high-nickel cathode material. Its microstructure is as follows: Figure 9 As shown.

[0217] Comparative Example 7

[0218] This comparative example prepares a high-nickel cathode material:

[0219] (1) Lithium hydroxide C and lithium hydroxide B are mixed in a mass ratio of 8:2 to obtain mixed lithium hydroxide;

[0220] (2) The precursor Ni with a molar ratio of 1:1.05 0.88 Co 0.10 Al 0.02(OH)2 and lithium hydroxide from step (1) are mixed using a high-speed mixer; sintered at 700℃ for 10 h, and the resulting powder is recorded as powder I-h, precursor D. 50 =13.5μm, D after calcination and pulverization 50 =13.0μm;

[0221] (3) Wash the powder I-h obtained in step (2) with pure water for 3 minutes, with a water-to-material mass ratio of 0.8:1 and a rotation speed of 150 Hz. After washing, dry it in a vacuum oven with a vacuum degree ≥0.06 MPa to obtain powder II-h;

[0222] (4) The powder II-h obtained in step (3) is sintered at 580℃ for 8 hours to obtain powder III-h, which is the high-nickel cathode material. Its microstructure is as follows: Figure 10 As shown.

[0223] Example 2

[0224] This embodiment prepares a high-nickel cathode material:

[0225] (1) Lithium hydroxide VII and lithium hydroxide VIII are mixed in a mass ratio of 8:2 to obtain mixed lithium hydroxide;

[0226] (2) The precursor Ni with a molar ratio of 1:1.05 0.88 Co 0.10 Al 0.02 (OH)2 and lithium hydroxide from step (1) were mixed using a high-speed mixer; sintered at 700℃ for 10 h, and the resulting powder was pulverized and designated as powder I-i, precursor D. 50 =13.5μm, D after calcination and pulverization 50 =13.0μm;

[0227] (3) Wash the powder I-i obtained in step (2) with pure water for 3 minutes, with a water-to-material mass ratio of 0.8:1 and a rotation speed of 150 Hz. After washing, dry it in a vacuum oven with a vacuum degree ≥0.06 MPa to obtain powder II-i;

[0228] (4) The powder II-i obtained in step (3) is sintered at 580℃ for 8 hours to obtain powder III-i, which is the high-nickel cathode material. Its microstructure is as follows: Figure 11 As shown.

[0229] Example 3

[0230] This embodiment prepares a high-nickel cathode material:

[0231] (1) Lithium hydroxide VII and lithium hydroxide VIII are mixed in a mass ratio of 7.5:2.5 to obtain mixed lithium hydroxide;

[0232] (2) The precursor Ni with a molar ratio of 1:1.05 0.88 Co 0.10 Al 0.02 (OH)2 and lithium hydroxide from step (1) were mixed using a high-speed mixer; sintered at 700℃ for 10 h, and the resulting powder was pulverized and designated as powder I-j, precursor D. 50 =13.5μm, D after calcination and pulverization 50 =13.0μm;

[0233] (3) Wash the powder I-j obtained in step (2) with pure water for 3 minutes, with a water-to-material mass ratio of 0.8:1 and a rotation speed of 150 Hz. After washing, dry it in a vacuum oven with a vacuum degree ≥0.06 MPa to obtain powder II-j;

[0234] (4) Sinter the powder II-j obtained in step (3) at 580℃ for 8 hours to obtain powder III-j, which is the high-nickel cathode material.

[0235] Example 4

[0236] This embodiment prepares a high-nickel cathode material:

[0237] (1) Lithium hydroxide VII and lithium hydroxide VIII are mixed at a mass ratio of 8.5:1.5 to obtain mixed lithium hydroxide;

[0238] (2) The precursor Ni with a molar ratio of 1:1.05 0.88 Co 0.10 Al 0.02 (OH)2 and lithium hydroxide from step (1) were mixed using a high-speed mixer; sintered at 700℃ for 10 h, and the resulting powder was pulverized and designated as powder I-k, precursor D. 50 =13.5μm, D after calcination and pulverization 50 =13.0μm;

[0239] (3) Wash the powder I-k obtained in step (2) with pure water for 3 minutes, with a water-to-material mass ratio of 0.8:1 and a rotation speed of 150 Hz. After washing, dry it in a vacuum oven with a vacuum degree ≥0.06 MPa to obtain powder II-k;

[0240] (4) The powder II-k obtained in step (3) is sintered at 580℃ for 8 hours to obtain powder III-k, which is the high-nickel cathode material.

[0241] Test case

[0242] The cathode materials obtained in the examples and comparative examples were used to fabricate lithium-ion batteries using the following methods:

[0243] (1) Preparation of positive electrode sheet: The positive electrode material, conductive carbon black and polyvinylidene fluoride (PVDF) are mixed and ground evenly in a mortar at a mass ratio of 8:1:1. During the grinding process, an appropriate amount of NMP is added dropwise to adjust the viscosity of the slurry. After thorough grinding, the slurry is evenly coated onto the current collector aluminum foil and dried at 80℃ for 2 days. After the electrode sheet is dried, it is cut into circular electrode sheets with a diameter of 15mm using a die-cutting machine. The mass of a single electrode sheet is weighed using an electronic balance and placed in a glove box (H2O concentration <1ppm, O concentration <0.2ppm) for later use.

[0244] (2) Button cell assembly: Using lithium sheet as negative electrode, and 1 mol / L LiPF6 dissolved in EC-EMC-DMC (volume ratio 1:1:1) as electrolyte, the button cell is assembled in a glove box filled with argon gas. From top to bottom, the components are: positive electrode shell, positive electrode sheet, electrolyte, separator, electrolyte, lithium sheet, and negative electrode shell.

[0245] The cathode materials and corresponding lithium-ion batteries prepared in the examples and comparative examples were subjected to the following tests, and the results are shown in Table 15:

[0246] (1) Initial discharge specific capacity: The test voltage was 2.50-4.25V, and the measurement was performed under 1C rate testing conditions. The initial charge-discharge curve is shown below. Figure 12 and 13 As shown.

[0247] (2) Cycle capacity retention: The test voltage is 2.50-4.25V, and the ratio of the discharge specific capacity after each cycle to the discharge specific capacity at the first cycle is measured under 1C rate test conditions. The curve of cycle capacity retention as a function of the number of cycles is shown below. Figure 14 and 15 As shown.

[0248] Table 15: Performance of lithium-ion batteries prepared from the cathode materials of the Examples and Comparative Examples

[0249]

[0250] from Figure 1 and Figure 2 It can be seen that by using crushing and sieving processes, followed by mixing, the particle size distribution of lithium hydroxide can be significantly changed, resulting in a mixed lithium hydroxide with a suitable ratio of lithium hydroxide particles of the desired size. This allows the prepared cathode material to have both high capacity and excellent cycle performance.

[0251] from Figure 3 and Figure 4 It can be seen that the cathode material obtained by sintering a mixture of lithium salts of varying sizes of lithium hydroxide particles ( Figure 3 Compared to the cathode materials produced by conventional lithium salt sintering ( Figure 4The primary particles in the secondary spheres are significantly different. The cathode material of this invention includes two types of secondary spheres: those formed by the agglomeration of large-sized primary particles and those formed by the agglomeration of small-sized primary particles. In contrast, the secondary spheres of the cathode material sintered from conventional lithium salts contain only primary particles of a single size.

[0252] Figure 5 , Figure 6 , Figure 10 and Figure 11 It can be seen that the cathode material prepared by mixing lithium hydroxide with a D50 difference of 10-12 μm between large and small particles in an appropriate ratio has two distinctly different primary particle morphologies in its secondary spherical particles. Figure 8 and Figure 9 It can be seen that the difference in D50 between using lithium hydroxide particles of different sizes is significant. Figure 8 Corresponding to a D50 difference of >12μm between large and small lithium hydroxide particles, Figure 9 For cathode materials prepared from mixed lithium hydroxide with a D50 difference of <10 μm between large and small lithium hydroxide particles, the secondary spheres of the cathode material exhibit various primary particle morphologies, and the primary particles are uneven in size. Figure 5-6 , Figure 10-11 and Figure 8-9 Comparison shows that cathode materials prepared by mixing lithium hydroxide with appropriate particle size difference and ratio can obtain a more ideal secondary spherical morphology. Figure 11 ).

[0253] As can be seen from Table 15, the cathode materials of Examples 1-4 prepared using mixed lithium hydroxide with appropriate particle size ratios exhibit both high capacity (indicated by an initial discharge specific capacity ≥193mAh / g) and excellent cycle performance (indicated by a capacity retention rate ≥92% after 50 cycles). In contrast, the cathode materials of Comparative Example 1 prepared using conventional doping and coating modification methods, Comparative Examples 2 and 3 prepared using mixed lithium hydroxide with inappropriate particle size ratios, Comparative Example 4 prepared using conventional particle size lithium hydroxide, Comparative Example 5 prepared using mixed lithium hydroxide with a particle size D50 difference >12μm, Comparative Example 6 prepared using mixed lithium hydroxide with a particle size D50 difference <10μm, and Comparative Example 7 prepared using mixed lithium hydroxide with a large Span value, failed to exhibit both high capacity and excellent cycle performance.

[0254] from Figure 12 and Figure 14 It can be seen that, compared with the cathode materials of Comparative Examples 1-4, the cathode material of Example 1 has both high capacity and excellent cycle performance; the capacity of Comparative Examples 1 and 3 is low, and the cycle performance of Comparative Examples 2 and 4 is poor.

[0255] from Figure 13 and Figure 15 It can be seen that, compared with the cathode materials of Comparative Examples 5-7, the cathode materials of Examples 2-4 have both high capacity and excellent cycle performance; the capacity of Comparative Examples 5 and 7 is lower, and the cycle performance of Comparative Example 6 is worse.

Claims

1. A secondary spherical cathode material, characterized in that, The secondary spherical cathode material comprises a first secondary sphere formed by the agglomeration of a first primary particle and a second secondary sphere formed by the agglomeration of a second primary particle. The particle size of the first primary particle is larger than that of the second primary particle. The secondary spherical cathode material is formed by sintering a mixture of mixed lithium salt particles and cathode material precursor. The mixed lithium salt particles include a first lithium salt particle and a second lithium salt particle with a mass ratio of 7.5:2.5 to 8.5:1.5, wherein the particle size D50 of the first lithium salt particle is 15-25 μm and the particle size D50 of the second lithium salt particle is 5-9 μm.

2. The secondary spherical cathode material as described in claim 1, characterized in that, The secondary spherical cathode material has one or more of the following characteristics: In the mixed lithium salt, the mass ratio of the first lithium salt particles to the second lithium salt particles is from 7.8:2.2 to 8.2:1.8, for example, 8:2; The particle size D50 of the first lithium salt particles is 17-20 μm, preferably 17-18 μm; The particle size D50 of the second lithium salt particles is 6-7 μm, preferably 6-6.5 μm; The particle size distribution Span value of the first lithium salt particles is ≤0.5; The particle size distribution Span value of the second lithium salt particles is ≤0.8; The difference between the particle size D50 of the first lithium salt particle and the particle size D50 of the second lithium salt particle is 10-12 μm. The lithium salt is selected from one or both of lithium hydroxide and lithium carbonate; The cathode material precursor is nickel cobalt manganese hydroxide, nickel cobalt aluminum hydroxide, or nickel cobalt manganese aluminum hydroxide; The particle size D50 of the cathode material precursor is 3-15 μm; The secondary spherical cathode material is a nickel-cobalt-manganese ternary cathode material, a nickel-cobalt-aluminum ternary cathode material, or a nickel-cobalt-manganese-aluminum quaternary cathode material. The secondary spherical cathode material is a medium-nickel cathode material or a high-nickel cathode material. In the medium-nickel cathode material, the amount of nickel element accounts for ≥60% and <80% of the total amount of nickel and M element. In the high-nickel cathode material, the amount of nickel element accounts for ≥80% and preferably 80%-96% of the total amount of nickel and M element. The M element is two or three of Co, Mn and Al. The molar ratio of the cathode material precursor to the mixed lithium salt particles is 1:(1-1.1).

3. A method for preparing the secondary spherical cathode material according to claim 1 or 2, characterized in that, The method includes the following steps: (1) The first lithium salt particles, the second lithium salt particles, the cathode material precursor and the optional dopant are mixed evenly to obtain a first mixture. (2) The first mixture is sintered once, and the sintered product is crushed to obtain the first powder; (3) The first powder is sintered twice to obtain the secondary spherical cathode material; or, the first powder is mixed evenly with a coating agent to obtain a second mixture, and the second mixture is sintered twice to obtain the secondary spherical cathode material.

4. The method as described in claim 3, characterized in that, The first lithium salt particles and the second lithium salt particles are obtained by crushing and sieving lithium salt raw material particles with a particle size D50≥200μm; Preferably, an air jet mill is used for pulverization; Preferably, the particle size D50 of the lithium salt raw material particles is 200-300 μm.

5. The method as described in claim 3, characterized in that, The method has one or more of the following characteristics: The temperature for the first sintering is 600-1000℃; The sintering time for one sintering cycle is 8-15 hours. The particle size D50 of the first powder is 3-15 μm; The dopant is a compound containing element A, wherein element A is selected from one or more of Li, Zr, Ti, Al, Mg, Co, Mn, Sr, Mo, Ne, B and F, and the mass of element A in the dopant preferably accounts for 0-1000 ppm of the mass of the first powder. The coating agent is a compound containing element B, wherein element B is selected from one or more of Li, Zr, Ti, Al, Mg, Co, Mn, Sr, Mo, Ne, B and F, and the mass of element B in the coating agent preferably accounts for 0-5000 ppm of the mass of the secondary spherical cathode material. The temperature for the secondary sintering is 100-700℃; The secondary sintering time is 2-15 hours.

6. The method as described in claim 3, characterized in that, The secondary spherical cathode material is a medium-nickel cathode material, and the method has one or more of the following characteristics: The temperature for the first sintering is 700-1000℃; The first mixture may or may not contain dopants; The first powder obtained in step (2) is directly processed in step (3).

7. The method as described in claim 3, characterized in that, The secondary spherical cathode material is a high-nickel cathode material, and the method has one or more of the following characteristics: The temperature for the first sintering is 600-800℃; The first mixture may or may not contain dopants; After washing and drying the first powder obtained in step (2), step (3) is carried out.

8. The method as described in claim 7, characterized in that, The method has one or more of the following characteristics: The water-to-material mass ratio for the washing process is (0.5-2):1; The washing time is 1-10 minutes; The water washing speed is 100-500Hz; The drying process is vacuum drying.

9. A positive electrode sheet, characterized in that, The positive electrode sheet contains the secondary spherical positive electrode material as described in claim 1 or 2.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode sheet as described in claim 9.

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