A ternary cathode active material and its preparation method, cathode sheet, and secondary battery

Abstract

This invention provides a ternary cathode active material, its preparation method, a cathode sheet, and a secondary battery. The ternary cathode active material comprises spherical or near-spherical secondary particles. Each secondary particle includes an inner layer and an outer layer covering at least a portion of the surface of the inner layer. The inner layer includes multiple inner primary particles, and the outer layer includes multiple outer primary particles. The average particle size of the inner primary particles is smaller than that of the outer primary particles. A portion of the inner primary particles and a portion of the outer primary particles interweave at the interface to form an interlaced layer; R1 / R0 = 1 / 2–4 / 5. The ternary cathode active material provided by this invention, through the formation of an interlaced layer, the limitation of the small size of the inner primary particles, the large size of the outer primary particles, and the limitation of the inner layer volume ratio, achieves a synergistic effect that balances the cycle stability and capacity of the ternary cathode active material, thereby balancing the cycle life and energy density of the secondary battery.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, and particularly relates to a ternary positive electrode active material and its preparation method, a positive electrode sheet, and a secondary battery. Background Technology

[0002] With the global energy structure shifting towards cleaner energy and the increasing demand for portability in consumer electronics, the new energy vehicle, large-scale energy storage systems, and high-end consumer electronics industries have experienced rapid development. As the core power source for these devices, the comprehensive performance of lithium-ion batteries, especially their energy density, cycle life, and rate performance, has become a key constraint on industrial progress. Among numerous cathode materials, ternary materials, represented by lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide, offer a crucial material foundation for achieving high energy density in batteries due to their high specific capacity and high operating voltage, thus becoming the focus of current research and application.

[0003] Despite the significant advantages of ternary materials in terms of energy density, their inherently insufficient cycle life has become a major bottleneck restricting their development in applications such as automotive power batteries and long-cycle energy storage, where lifespan and reliability are of paramount importance.

[0004] Therefore, developing a long-life ternary cathode active material has become a technical challenge that the industry urgently needs to solve. Summary of the Invention

[0005] This invention provides a ternary cathode active material, which has excellent structural stability and high capacity, and can improve the cycle life and energy density of secondary batteries.

[0006] This invention provides a method for preparing a ternary cathode active material. The ternary cathode active material prepared by this method has excellent structural stability and high capacity, which can improve the cycle life and energy density of secondary batteries.

[0007] The present invention also provides a positive electrode sheet that can improve the cycle life and energy density of a secondary battery.

[0008] The present invention also provides a secondary battery with excellent cycle performance and energy density.

[0009] The first aspect of the present invention provides a ternary cathode active material, comprising spherical or near-spherical secondary particles, wherein the secondary particles include an inner layer and an outer layer covering at least a portion of the surface of the inner layer, the inner layer includes a plurality of inner layer primary particles, the outer layer includes a plurality of outer layer primary particles, the average particle size of the inner layer primary particles is smaller than the average particle size of the outer layer primary particles, and a portion of the inner layer primary particles and a portion of the outer layer primary particles interweave at the interface to form an interleaved layer;

[0010] R1 / R0 = 1 / 2 - 4 / 5; where the center of the secondary particle is C and the radius is R0; in the secondary particle, with C as the center, R1 is the radius of the inner layer.

[0011] The ternary cathode active material as described above, wherein R1 / R0 = 7 / 10-4 / 5; and / or,

[0012] The average aspect ratio a of the inner primary particles is ≥1.8, preferably 2≤a≤3; and / or,

[0013] The average aspect ratio b of the outer primary particles is ≤2, preferably 1.2 ≤ b ≤ 1.7; and / or,

[0014] The average particle size of the inner layer primary particles is 150-350 nm, preferably 180-300 nm; and / or,

[0015] The average particle size of the outer primary particles is 200-450 nm, preferably 250-400 nm.

[0016] In the ternary cathode active material described above, the thickness of the interlaced layer is 50-500 nm, preferably 100-300 nm.

[0017] The ternary cathode active material as described above, wherein the average porosity of the inner layer is less than the average porosity of the outer layer; and / or, the average porosity of the ternary cathode active material is <0.5%.

[0018] The ternary cathode active material described above, wherein the average particle size of the ternary cathode active material is 10-16 μm; and / or,

[0019] The average porosity of the inner layer is 0.1-0.75%; and / or,

[0020] The average porosity of the outer layer is 0.36-1.78%.

[0021] The ternary cathode active material described above, wherein the general formula of the ternary cathode active material is Li 1+a [Ni x Co y Mn z M1 m M2 n O 2±c A dWhere 0.6 ≤ x < 1, 0 <y<0.3,0<z<0.3,0<a<0.2,c<0.02,0≤d≤0.05,x+y+z+m+n=1,0.0005≤m≤0.005,0.0005≤n≤0.005;

[0022] M1 includes at least one of W, Mo, and Ta; M2 includes at least one of Zr, Sr, Nb, and Ce; and A includes at least one of F and S.

[0023] A second aspect of the present invention provides a method for preparing the ternary cathode active material, comprising the following steps:

[0024] Under alkaline conditions, a first coprecipitation reaction is carried out using a first raw material solution including a metal source and a first dopant element source to obtain a first intermediate; a second coprecipitation reaction is carried out using a second raw material solution including the metal source and the first intermediate to obtain a second intermediate; a third coprecipitation reaction is carried out using a third raw material solution including the metal source, the second intermediate, and a second dopant element source to obtain a ternary cathode active material precursor; wherein, the average particle size of the first intermediate is 1 / 2 to 4 / 5 of the target average particle size of the ternary cathode active material;

[0025] The ternary cathode active material is obtained by sintering a mixed raw material comprising the ternary cathode active material precursor and a lithium source.

[0026] The first doping element source includes at least one of W source, Mo source, and Ta source.

[0027] The second doping element source includes at least one of Zr source, Sr source, Nb source, and Ce source.

[0028] In the preparation method described above, the concentration of the metal source in the first raw material solution is 1.5-2.5 mol / L; and / or,

[0029] The concentration of the metal source in the third raw material solution is 1.5-2.5 mol / L; and / or,

[0030] The molar concentration of the first dopant source is less than the molar concentration of the second dopant source; and / or,

[0031] The metal source includes a nickel source, and the molar concentration of the nickel source in the third raw material solution is greater than the molar concentration of the nickel source in the first raw material solution; and / or,

[0032] The average particle size of the second intermediate is 13 / 25-17 / 20 of the target average particle size of the ternary cathode active material; and / or,

[0033] The sintering process specifically includes the following steps: the ternary cathode active material precursor is sintered at 400-600℃ for 2-5 hours to obtain a first sintered product; the first sintered product is mixed with a portion of lithium salt and then sintered at 500-700℃ for 1-3 hours to obtain a second sintered product; the second sintered product is mixed with the remaining lithium salt and then sintered at 700-950℃ for 8-25 hours to obtain the ternary cathode active material; wherein the mass ratio of the portion of lithium salt to the remaining lithium salt is (30-60):(70-40), preferably (50-60):(50-40).

[0034] A third aspect of the present invention provides a positive electrode sheet comprising the ternary positive electrode active material described in the first aspect above, or the ternary positive electrode active material prepared by the preparation method described in the second aspect above.

[0035] A fourth aspect of the present invention provides a secondary battery comprising the ternary positive electrode active material described in the first aspect above, or the ternary positive electrode active material prepared by the preparation method described in the second aspect above, or the positive electrode sheet described in the third aspect above.

[0036] The ternary cathode active material provided by this invention suppresses grain boundary cracking and particle breakage during cycling through interleaved layers, thereby extending the service life of the ternary cathode active material and improving the cycle life of the secondary battery. By limiting the small size of the inner primary particles to improve specific surface area and capacity utilization, and the large size of the outer primary particles to enhance electrolyte wettability, the two work synergistically to balance capacity and cycle stability. At the same time, by limiting the volume ratio of the inner layer, both structural strength and electrolyte wettability are taken into account. The synergistic effect of these three factors balances the cycle stability and capacity of the ternary cathode active material, thereby balancing the cycle life and energy density of the secondary battery. Attached Figure Description

[0037] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0038] Figure 1 This is a cross-sectional SEM image of the ternary cathode active material particles provided in Embodiment 1 of the present invention;

[0039] Figure 2 This is a cross-sectional SEM image of the ternary cathode active material particles provided in Embodiment 22 of the present invention;

[0040] Figure 3 This is the EDS diagram of the ternary cathode active material provided in Embodiment 1 of the present invention.

[0041] The accompanying drawings have illustrated specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to specific embodiments. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0043] To improve the cycle life of ternary cathode active materials, the inventors conducted in-depth research on existing systems, represented by lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. The research revealed that the root cause of their poor cycle performance lies in the structural instability that easily occurs during long-term cycling, specifically manifested as lattice distortion, grain boundary cracking, and secondary particle breakage, thus affecting the cycle life of the secondary battery.

[0044] To address the aforementioned problems, the inventors attempted modification strategies such as surface coating (e.g., carbon, metal oxides) or bulk element doping (e.g., Al, Mg) to enhance structural stability. However, in this process, the inventors found that while surface coatings hinder side reactions, they also impede the migration of active ions, and conventional homogeneous doping may sacrifice some reversible capacity while stabilizing the lattice structure. Therefore, none of the above methods can simultaneously meet the requirements of high capacity and high structural stability.

[0045] Based on this, the inventors proposed the ternary cathode active material of this invention, aiming to achieve both high structural stability and high capacity.

[0046] The first aspect of the present invention provides a ternary positive electrode active material, comprising spherical or near-spherical secondary particles, wherein the secondary particles include an inner layer and an outer layer covering at least a portion of the surface of the inner layer, the inner layer includes a plurality of inner layer primary particles, the outer layer includes a plurality of outer layer primary particles, the average particle size of the inner layer primary particles is smaller than the average particle size of the outer layer primary particles, and a portion of the inner layer primary particles and a portion of the outer layer primary particles interweave at the interface to form an interleaved layer.

[0047] R1 / R0 = 1 / 2 - 4 / 5; where the center of the secondary particle is C and the radius is R0; in the secondary particle, with C as the center, R1 is the radius of the inner layer.

[0048] In this application, spherical or near-spherical secondary particles refer to secondary particles formed by the aggregation of multiple nano- or micron-sized primary particles as the basic unit of the ternary cathode active material. Their morphology satisfies either spherical (distance deviation from any point on the particle surface to the center ≤ 5%) or near-spherical (e.g., ellipsoidal, oblate, distance deviation from any point on the particle surface to the center ≤ 15%), which can be confirmed by scanning electron microscopy. The center of the sphere, C, refers to the geometric center of the spherical or near-spherical secondary particle. For example, by using image processing software to fit the contour of the SEM image of the secondary particle, the circumcircle (or near-circumcircle) of the particle contour can be calculated, and the center of this circumcircle is the center of the sphere, C. Alternatively, for irregular near-spherical particles in actual production, the center of the sphere can be taken as the intersection of the lines connecting the longest and shortest diameters of the particle. R0 refers to the maximum distance from the center C of the secondary particle to the particle surface, which is the radius of the circumscribed circle (or half of the longest diameter). The radius can be obtained, for example, by testing with a particle size analyzer. R1 refers to the distance from the center C of the secondary particle to the interface between the inner layer and the cross-layer.

[0049] In this application, a sphere is formed by extending from the center C of the sphere in any direction to 1 / 2-4 / 5 of the sphere. The area enclosed by this sphere is the inner layer. The part where the primary particles of the inner layer and the primary particles of the outer layer intersect is the interlaced layer. The annular area extending from the interface of the interlaced layer away from the inner layer in any direction to the outer surface of the secondary particles is the outer layer.

[0050] For example, R1 / R0 is 1 / 2, 3 / 5, 13 / 20, 7 / 10, 3 / 4, 39 / 50 or 4 / 5, or a range of any two of these values.

[0051] The ternary cathode active material provided by this invention exhibits excellent structural stability and high capacity, thereby improving the cycle life and energy density of secondary batteries. This is due to two main reasons: First, the interlocking layer formed by the interleaved inner and outer primary particles has a fused structure, which suppresses grain boundary cracking and particle breakage during cycling, thus improving the structural stability of the ternary cathode active material and enhancing the cycle life of the secondary battery. Second, the small average particle size of the inner primary particles increases specific surface area and capacity utilization, while the large average particle size of the outer primary particles enhances electrolyte wettability and structural strength. Simultaneously, the inner layer radius ratio is within a specific range (R1 / R0 = 1 / 2-4 / 5), further balancing structural strength and electrolyte wettability. The synergistic effect of these three factors balances the cycle stability and capacity of the ternary cathode active material, thereby balancing the cycle life and energy density of the secondary battery.

[0052] In one specific implementation, R1 / R0 = 7 / 10-4 / 5. A ratio of R1 to R0 within this range is more conducive to balancing the structural strength of the ternary cathode active material and the electrolyte wettability, resulting in better cycle life and energy density of the secondary battery.

[0053] In one specific embodiment, the average aspect ratio a of the inner primary particles is ≥1.8, preferably 2≤a≤3. A larger average aspect ratio allows the inner primary particles to preferentially grow radially, further shortening the ion diffusion distance and improving the rate performance of the secondary battery.

[0054] For example, the average aspect ratio α of the inner primary particles is 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3 or more, or a range of any two of these values.

[0055] The method for testing the average aspect ratio of the inner primary particles in this invention is as follows: In a two-dimensional image obtained by scanning electron microscopy (SEM), find a rectangle with the smallest area that can completely surround the projection of the inner primary particle. The longer side of this rectangle is defined as the length of the inner primary particle, and the shorter side is defined as the width of the inner primary particle. The aspect ratio of a single inner primary particle is then obtained by calculating the ratio of the two sides.

[0056] Based on the above measurement results of at least 5 randomly selected inner primary particles, the arithmetic mean of all aspect ratio values ​​is taken as the average aspect ratio of the inner primary particles.

[0057] In one specific embodiment, the average aspect ratio b of the outer primary particles is ≤2, preferably 1.2≤b≤1.7. A smaller average aspect ratio and moderate axial growth of the outer primary particles enhance the mechanical interlocking between particles, suppress structural instability during cycling, and improve the cycle performance of the secondary battery.

[0058] For example, the average aspect ratio b of the outer primary particles is 2, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2 or less, or a range of any two of these values.

[0059] The average aspect ratio of the outer primary particles is determined using the same method as the average aspect ratio of the inner primary particles, which will not be repeated here.

[0060] In one specific embodiment, the average particle size of the inner layer primary particles is 150-350 nm, preferably 180-300 nm. The average particle size of the inner layer primary particles within this range further enhances their specific surface area and capacity utilization, thereby increasing the energy density of the secondary battery.

[0061] For example, the average particle size of the inner primary particles is 150 nm, 180 nm, 200 nm, 250 nm, 300 nm or 350 nm, or a range of any two of these values.

[0062] In one specific embodiment, the average particle size of the outer primary particles is 200-450 nm, preferably 250-400 nm. An average particle size within this range further enhances electrolyte wettability and structural strength, thereby improving the cycle life of the secondary battery.

[0063] For example, the average particle size of the outer primary particles is 200 nm, 250 nm, 300 nm, 350 nm, 400 nm or 450 nm, or a range of any two of these values.

[0064] In one specific embodiment, the thickness of the interlaced layer is 50-500 nm, preferably 100-300 nm. Within this range, the thickness of the interlaced layer enhances structural strength while ensuring the ion diffusion rate, thereby improving the cycle performance and rate performance of the secondary battery.

[0065] For example, the average particle size of the outer primary particles is 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm or 500nm, or a range of any two of these values.

[0066] In one specific embodiment, the average porosity of the inner layer is lower than that of the outer layer. The low porosity design of the inner layer reduces structural defects, while the high porosity design of the outer layer promotes electrolyte wetting. The combination of these two features suppresses interfacial side reactions, improves the long-term cycle stability of the ternary cathode active material, and thus enhances the cycle life of the secondary battery.

[0067] In one specific embodiment, the average porosity of the ternary cathode active material is <0.5%. The low average porosity of the ternary cathode active material improves the particle strength of the ternary cathode active material, thereby enhancing its structural stability.

[0068] For example, the average porosity of the ternary cathode active material is 0.49%, 0.47%, 0.45%, 0.43%, 0.41%, 0.39%, 0.37%, 0.35%, 0.33% or less, or a range consisting of any two of these values.

[0069] In one specific embodiment, the average particle size of the ternary cathode active material is 10-16 μm. Within this average particle size range, the ternary cathode active material can balance compaction density and active ion transport efficiency, thereby enabling the secondary battery to achieve both energy density and rate performance.

[0070] For example, the average particle size of the ternary cathode active material is 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm or 16 μm, or a range of any two of these values.

[0071] The average particle size of the ternary cathode active material of the present invention was obtained by laser particle size analyzer.

[0072] In one specific embodiment, the average porosity of the inner layer is 0.1-0.75%. Within this range, the inner layer has a higher density, which is more conducive to improving the structural strength of the ternary cathode active material.

[0073] For example, the average porosity of the inner layer is 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, or 0.75%, or a range of any two of these values.

[0074] In one specific embodiment, the average porosity of the outer layer is 0.36-1.78%. Within this range, the outer layer has a lower density, which is more conducive to electrolyte wetting and further improves the rate performance of the secondary battery.

[0075] For example, the average porosity of the ternary cathode active material is 0.36%, 0.56%, 0.76%, 0.86%, 0.96%, 1.16%, 1.36%, 1.56%, 1.76%, or 1.78%, or a range of any two of these values.

[0076] In one specific embodiment, the general formula of the ternary cathode active material is Li. 1+a [Ni x Co y Mn z M1 m M2 n O 2± c A d Where 0.6 ≤ x < 1, 0 <y<0.3,0<z<0.3,0<a<0.2,c<0.02,0≤d≤0.05,x+y+z+m+n=1,0.0005≤m≤0.005,0.0005≤n≤0.005;

[0077] M1 includes at least one of W, Mo, and Ta; M2 includes at least one of Zr, Sr, Nb, and Ce; and A includes at least one of F and S. M1 suppresses lattice distortion, M2 promotes particle growth, and A reduces interfacial side reactions. The synergistic effect of these multiple elements improves the cycle life and energy density of the secondary battery.

[0078] For example, x is 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or 0.99, or a range of any two of these values.

[0079] For example, y is 0.1, 0.13, 0.15, 0.17, 0.2, 0.22, 0.25, 0.27 or 0.29, or a range of any two of these values.

[0080] For example, z is 0.1, 0.13, 0.15, 0.17, 0.2, 0.22, 0.25, 0.27 or 0.29, or a range of any two of these values.

[0081] For example, a is 0.01, 0.03, 0.05, 0.07, 0.09, 0.11, 0.13, 0.15, 0.17 or 0.19, or a range of any two of these values.

[0082] For example, c is 0.019, 0.018, 0.017, 0.016, 0.015, 0.014, 0.013, 0.012 or less, or a range of any two of these values.

[0083] For example, d is 0, 0.01, 0.02, 0.03, 0.04 or 0.05, or a range of any two of these values.

[0084] For example, m is 0.0005, 0.001, 0.0015, 0.002, 0.0025, 0.003, 0.0035, 0.004, 0.0045 or 0.005, or a range of any two of these values.

[0085] For example, n is 0.0005, 0.001, 0.0015, 0.002, 0.0025, 0.003, 0.0035, 0.004, 0.0045 or 0.005, or a range of any two of these values.

[0086] A second aspect of this invention provides a method for preparing a ternary cathode active material, comprising the following steps:

[0087] Under alkaline conditions, a first coprecipitation reaction is carried out using a first raw material solution including a metal source and a first dopant element source to obtain a first intermediate; a second coprecipitation reaction is carried out using a second raw material solution including a metal source and the first intermediate to obtain a second intermediate; a third coprecipitation reaction is carried out using a third raw material solution including a metal source, the second intermediate, and a second dopant element source to obtain a ternary cathode active material precursor; wherein, the average particle size of the first intermediate is 1 / 2 to 4 / 5 of the target average particle size of the ternary cathode active material;

[0088] Ternary cathode active materials are obtained by sintering a mixture of raw materials, including ternary cathode active material precursors and lithium sources.

[0089] The first doping element source includes at least one of W source, Mo source, and Ta source.

[0090] The second doping element source includes at least one of Zr source, Sr source, Nb source, and Ce source.

[0091] It should be noted that the chemical formula of the ternary cathode active material precursor is Ni. x Co y Mn z M1 m M2 n (OH)₂, where 0.6 ≤ x < 1, 0 <y<0.3,0<z<0.3,0.0005≤m≤0.005,0.0005≤n≤0.005。

[0092] In detail, the metal source refers to the chemical composition used to form the secondary particles of the ternary cathode active material, such as nickel, cobalt, and manganese (aluminum). The aforementioned first doping element source has a particle refining effect, acting as a refining agent to inhibit the growth of inner primary particles during sintering (especially inhibiting the increase in the width of inner primary particles); the aforementioned second doping element source has a particle growth promoting effect, acting as a flux to promote the rapid growth of outer primary particles during sintering (especially promoting the increase in the width of outer primary particles). The first raw material solution, including the metal source and the first doping element source, undergoes a first co-precipitation reaction until the average particle size of the first intermediate is 1 / 2 to 4 / 5 of the target average particle size of the ternary cathode active material.

[0093] Subsequently, a second coprecipitation reaction is carried out on a second raw material solution including a metal source and a first intermediate to obtain a second intermediate; then, a third raw material solution including a metal source, a second intermediate, and a second dopant element source is carried out on a third coprecipitation reaction to obtain a ternary cathode active material precursor.

[0094] The present invention does not specifically limit the average particle size of the first intermediate and the second intermediate. In one embodiment, the average particle size of the first intermediate is 5-12.8 μm and the average particle size of the second intermediate is 5.1-13.3 μm.

[0095] In addition to the metal source and the first dopant element source, the first raw material solution also includes a precipitant, a complexing agent, and a solvent. For example, the precipitant can be sodium hydroxide, the complexing agent can be ammonia, and the solvent can be deionized water. This invention does not specifically limit the concentrations of the precipitant and the complexing agent. In one embodiment, the concentration of the precipitant is 6.0-10.0 mol / L, and the concentration of the complexing agent is 4.4-6.0 mol / L.

[0096] Subsequently, the mixed raw materials, including the ternary cathode active material precursor and the lithium source, are sintered to obtain the ternary cathode active material.

[0097] This invention achieves a multi-level structural design for ternary cathode active materials through segmented co-precipitation: In the segmented co-precipitation process, the segmented addition of the first and second doping element sources allows the inner and outer primary particles to form an interlocking structure during growth, effectively suppressing grain boundary cracking and particle breakage; During sintering, the first doping element source inhibits excessive growth of the inner primary particles, while the second doping element source promotes rapid growth of the outer primary particles, achieving a size difference between the inner and outer primary particles and balancing the capacity and cycle stability of the ternary cathode active material; Simultaneously, by limiting the average particle size of the first intermediate to 1 / 2-4 / 5 of the average particle size of the ternary cathode active material, the ternary cathode active material achieves a balance between structural strength and electrolyte wettability; The synergistic effect of the above methods improves structural strength while balancing the contradiction between capacity utilization and cycle life.

[0098] In this invention, W source refers to the raw material providing tungsten, Mo source refers to the raw material providing molybdenum, Ta source refers to the raw material providing tantalum, Zr source refers to the raw material providing zirconium, Sr source refers to the raw material providing strontium, Nb source refers to the raw material providing niobium, and Ce source refers to the raw material providing cerium.

[0099] This invention does not limit the specific conditions of the first coprecipitation reaction, the second coprecipitation reaction, and the third coprecipitation reaction.

[0100] In one embodiment, the temperature of the first coprecipitation reaction is 45-60°C. At this reaction temperature, the first coprecipitation reaction can proceed rapidly and efficiently.

[0101] For example, the temperature of the first coprecipitation reaction is 45°C, 47°C, 49°C, 51°C, 53°C, 55°C, 57°C, or 60°C, or a range of any two of these values.

[0102] In one embodiment, the temperature of the second coprecipitation reaction is 45-60°C. At this reaction temperature, the second coprecipitation reaction can proceed rapidly and efficiently.

[0103] For example, the temperature of the second coprecipitation reaction is 45°C, 47°C, 49°C, 51°C, 53°C, 55°C, 57°C or 60°C, or a range of any two of these values.

[0104] In one embodiment, the temperature of the third coprecipitation reaction is 45-60°C. At this reaction temperature, the third coprecipitation reaction can proceed rapidly and efficiently.

[0105] For example, the temperature of the third coprecipitation reaction is 45°C, 47°C, 49°C, 51°C, 53°C, 55°C, 57°C or 60°C, or a range of any two of these values.

[0106] In this invention, the temperatures of the first coprecipitation reaction, the second coprecipitation reaction, and the third coprecipitation reaction can be the same or different.

[0107] This invention does not specifically limit the time of the first coprecipitation reaction, the second coprecipitation reaction, and the third coprecipitation reaction, as long as the target first intermediate, the second intermediate, and the ternary cathode active material precursor can be obtained.

[0108] This invention does not specifically limit the reaction equipment; conventional equipment in the field can be used, such as a reaction vessel.

[0109] To obtain alkaline conditions, ammonia water is first added to the reaction vessel as a base liquid. The present invention does not specifically limit the concentration of ammonia water. In one embodiment, the concentration of ammonia water is 1.1-1.5 mol / L.

[0110] The present invention does not specify the amount of ammonia added. In one embodiment, the amount of ammonia added is 1 / 3 to 1 / 2 of the volume of the reaction vessel.

[0111] To further improve the structural stability and capacity of the prepared ternary cathode active material, the specific pH value, stirring speed, and feeding time under alkaline conditions were controlled.

[0112] In one embodiment, the stirring speed is controlled at 400-1000 rpm, and the feeding time is controlled at 10-30 h.

[0113] To ensure the precipitation reaction proceeds fully, low-intensity stirring is maintained for 10-12 hours after the third coprecipitation reaction feed is completed. This invention does not specify a particular stirring speed; in one embodiment, the stirring speed is 200-400 rpm.

[0114] In one specific embodiment, the concentration of the metal source in the first raw material solution is 1.5-2.5 mol / L. This concentration range allows for a balance between crystal growth rate and nucleation uniformity.

[0115] For example, the concentration of the metal source in the first raw material solution is 1.5 mol / L, 1.7 mol / L, 1.9 mol / L, 2.1 mol / L, 2.3 mol / L or 2.5 mol / L, or a range consisting of any two of these values.

[0116] In one specific embodiment, the concentration of the metal source in the third raw material solution is 1.5-2.5 mol / L. Within this range, the concentration of the metal source in the third raw material solution can balance crystal growth rate and nucleation uniformity.

[0117] For example, the concentration of the metal source in the third raw material solution is 1.5 mol / L, 1.7 mol / L, 1.9 mol / L, 2.1 mol / L, 2.3 mol / L or 2.5 mol / L, or a range of any two of these values.

[0118] In this invention, the concentration of the metal source in the first raw material solution and the concentration of the metal source in the third raw material solution can be the same or different.

[0119] In one specific embodiment, the molar concentration of the first dopant source is less than the molar concentration of the second dopant source. This configuration, through gradient concentration control, promotes uniform diffusion of elements, forming a concentration gradient in the cross-layer, reducing interfacial stress in the cross-layer, improving structural compatibility, and reducing crack formation during cycling. Simultaneously, the lower molar concentration of the first dopant source is beneficial for forming inner primary particles with a higher aspect ratio, shortening ion diffusion distance, and improving rate performance; the higher molar concentration of the second dopant source, resulting in a higher content of the second dopant source in the third raw material solution, further promotes the growth of the width of the outer primary particles, forming outer primary particles with a smaller aspect ratio, enhancing the structural strength of the ternary cathode active material, and improving the cycle performance of the secondary battery.

[0120] The present invention does not specifically limit the molar concentration of the first doping element source and the molar concentration of the second doping element source. In one embodiment, the molar concentration of the first doping element source is 0.01-0.3 mol / L and the molar concentration of the second doping element source is 0.01-0.3 mol / L.

[0121] In one specific embodiment, the metal source includes a nickel source, and the molar concentration of the nickel source in the third raw material solution is greater than the molar concentration of the nickel source in the first raw material solution. The higher molar concentration of the nickel source in the third raw material solution can balance the capacity of the ternary cathode active material and the electrolyte wettability, thereby balancing the energy density and cycle life of the secondary battery.

[0122] To further promote the occurrence of the first and third coprecipitation reactions, the pH of the first and third coprecipitation reactions can be controlled.

[0123] In one embodiment, the pH of the first coprecipitation reaction is 10-12.3, and the pH of the third coprecipitation reaction is 10.5-13.

[0124] In one specific embodiment, the average particle size of the second intermediate is 13 / 25-17 / 20 of the target average particle size of the ternary cathode active material. The average particle size of the second intermediate within this range ensures the thickness of the interlaced layer (50-500 nm), thereby ensuring the structural strength of the ternary cathode active material while also considering the active ion diffusion rate, thus guaranteeing the cycle performance and rate performance of the secondary battery.

[0125] For example, the average particle size of the second intermediate is 13 / 25, 3 / 5, 2 / 3, 7 / 10, 3 / 4, 4 / 5 or 17 / 20 of the target average particle size of the ternary cathode active material, or a range consisting of any two of these values.

[0126] In one specific embodiment, the sintering process includes the following steps: a ternary cathode active material precursor is sintered at 400-600℃ for 2-5 hours to obtain a first sintered product; the first sintered product is mixed with a portion of lithium salt, and then sintered at 500-700℃ for 1-3 hours to obtain a second sintered product; the second sintered product is mixed with the remaining lithium salt, and then sintered at 700-950℃ for 8-25 hours to obtain the ternary cathode active material; wherein the mass ratio of the portion of lithium salt to the remaining lithium salt is (30-60):(70-40), preferably (50-60):(50-40). The multi-stage sintering process, through temperature gradient control, ensures the uniform distribution of doping elements (the first doping element and the second doping element) in the crystal lattice, thereby balancing the contradiction between capacity utilization and cycle life while improving structural strength.

[0127] Preferably, the first sintering temperature is 500-600℃ and the time is 3-5h, and the second sintering temperature is 550-650℃ and the time is 2-3h.

[0128] For example, the temperature of the first sintering is 400°C, 430°C, 460°C, 490°C, 520°C, 550°C, 580°C or 600°C, or a range of any two of these values.

[0129] For example, the first sintering time is 2h, 2.4h, 2.8h, 3.2h, 3.6h, 4h, 4.4h, 4.8h or 5h, or a range of any two of these values.

[0130] For example, the second sintering temperature is 500°C, 520°C, 540°C, 560°C, 580°C, 600°C, 620°C, 640°C, 660°C, 680°C, or 700°C, or a range of any two of these values.

[0131] For example, the second sintering time is 1h, 1.4h, 1.8h, 2h, 2.4h, 2.8h or 3h, or a range of any two of these values.

[0132] For example, the temperature of the third sintering is 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, 820°C, 840°C, 860°C, 880°C, 900°C, 920°C, or 950°C, or a range of any two of these values.

[0133] For example, the third sintering time is 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 25h, or a range of any two of these values.

[0134] For example, the mass ratio of a portion of the lithium salt to the remaining lithium salt is 30:70, 40:60, 50:50, or 60:40, or a range consisting of any two of these values.

[0135] To further reduce interfacial side reactions, source A can be added during the second sintering process. In one embodiment, source A includes at least one of lithium fluoride and lithium sulfide. The present invention does not impose a specific limit on the amount of source A added, and it can be adjusted according to actual needs.

[0136] The present invention does not specifically limit the type of lithium salt. In one embodiment, the lithium salt includes, but is not limited to, lithium carbonate.

[0137] A third aspect of this invention provides a positive electrode sheet comprising the ternary positive electrode active material described in the first aspect, or the ternary positive electrode active material prepared by the preparation method described in the second aspect. Because this positive electrode sheet comprises the aforementioned ternary positive electrode active material, it can effectively improve the cycle life and energy density of a secondary battery.

[0138] The present invention does not specifically limit the structure of the positive electrode sheet. In one embodiment, the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least a portion of the surface of the positive current collector. The positive active layer includes the above-mentioned ternary positive active material, conductive agent and binder.

[0139] This invention does not specifically limit the material of the positive electrode current collector; it can be any material conventional in the art. For example, the material of the positive electrode current collector can be either aluminum foil or nickel foil.

[0140] This invention does not specifically limit the type of conductive agent; it can be any material conventional in the art. For example, the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber.

[0141] This invention does not specifically limit the type of adhesive, which can be a conventional material in the art. For example, the adhesive can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0142] This invention does not specifically limit the preparation method of the positive electrode sheet. In one embodiment, the positive electrode sheet can be prepared by a method including the following steps:

[0143] The ternary positive electrode active material of the present invention is dispersed with a conductive agent and a binder in an N-methylpyrrolidone (NMP) solvent and thoroughly stirred to form a uniform positive electrode slurry. The positive electrode slurry is then uniformly coated onto a positive electrode current collector, and after drying, rolling and slitting, a positive electrode sheet is obtained.

[0144] This invention does not impose specific limitations on the amount of ternary cathode active material, conductive agent and binder, and can be adjusted according to the actual situation.

[0145] A fourth aspect of the present invention provides a secondary battery comprising the ternary cathode active material described in the first aspect, or the ternary cathode active material prepared by the method described in the second aspect, or the cathode sheet described in the third aspect. Therefore, this secondary battery exhibits excellent cycle performance and energy density.

[0146] It is conceivable that, in addition to the aforementioned positive electrode, the secondary battery of the present invention also includes a negative electrode, an electrolyte, and a separator.

[0147] The present invention does not specifically limit the structure of the negative electrode sheet. In one embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least a portion of the surface of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, a binder, and a conductive agent.

[0148] This invention does not specifically limit the material of the negative electrode current collector; it can be any conventional material in the art. For example, the negative electrode current collector can be any of copper foil, nickel foam, or copper foam.

[0149] This invention does not specifically limit the type of negative electrode active material, and it can be any negative electrode active material commonly used in batteries. For example, the negative electrode active material can be selected from at least one of graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrodes), tin-based negative electrode materials (mainly including tin and tin alloys).

[0150] This invention does not specifically limit the type of binder; it can be any binder commonly used in battery negative electrodes. For example, the binder can be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0151] This invention does not specifically limit the type of conductive agent; it can be any conductive agent commonly used in the negative electrode of batteries. For example, the conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene.

[0152] This invention does not specifically limit the preparation method of the negative electrode sheet. In one embodiment, the negative electrode sheet can be prepared by a method including the following steps:

[0153] The negative electrode active material, conductive agent, and binder are dispersed in deionized water and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, a negative electrode sheet is obtained.

[0154] This invention does not impose specific limits on the amount of negative electrode active material, conductive agent, and binder, and these amounts can be adjusted according to actual conditions.

[0155] This invention does not specifically limit the composition of the electrolyte, which may include one or more solvents commonly used in current battery electrolytes, as well as lithium salts commonly used in current battery electrolytes. For example, the solvent may include at least one of ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, and γ-butyrolactone; the lithium salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFVI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFVI).

[0156] This invention does not specifically limit the material of the separator; it can be any separator material commonly used in batteries. For example, the separator can be selected from any of the following: polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven fabric separator, and separator with ceramic coating.

[0157] This invention does not specifically limit the preparation method of secondary batteries. In one embodiment, the secondary battery can be prepared by a method including the following steps:

[0158] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are wound or stacked to obtain a bare cell, which is then packaged into a pre-stamped aluminum-plastic film bag. After the packaged battery is dried, electrolyte is injected into the dried battery. After the battery is placed, formed, and resealed, the secondary battery is completed.

[0159] The present invention will be further described below through specific embodiments.

[0160] Example 1

[0161] A method for preparing a ternary cathode active material includes:

[0162] (1) According to the molar ratio of Ni:Co:Mn=63:10:27, nickel sulfate, cobalt sulfate and manganese sulfate (metal source) were prepared into a mixed solution (main element solution) using deionized water. Ammonium tungstate, the first dopant element source, was added to the mixed solution to obtain a mixed salt solution a1 (i.e., the first raw material solution). The total concentration of Ni, Co and Mn metal ions in the mixed salt solution a1 was 2 mol / L (the molar concentration of nickel was 1.26 mol / L), and the concentration of tungsten was 0.03 mol / L. Sodium hydroxide was prepared into an 8 mol / L alkaline solution using deionized water as a precipitant. 5.5 mol / L ammonia water was used as a complexing agent. Ammonia water with a concentration of 1.3 mol / L was used as the base solution, and the pH was adjusted to 12.3 using the precipitant.

[0163] Add the bottom liquid, which has a total volume of 1 / 3, to the reactor. Purge with nitrogen to replace the air. Turn on the stirring and heating to maintain the reaction temperature in the reactor at 50°C and the stirring speed at 800 rpm. Inject the mixed salt solution, complexing agent, and precipitant into the reactor and carry out the first coprecipitation reaction to obtain the first intermediate. The average particle size of the first intermediate is 11.3 μm (i.e., the average particle size of the first intermediate is 4 / 5 of the target average particle size of the ternary cathode active material).

[0164] (2) With the other parameters unchanged, continue to pass the mixed solution through the mixture to allow the mixed solution and the first intermediate (i.e., the second raw material solution) to continue the second coprecipitation reaction. Stop passing the mixed solution through the mixture after 2 minutes and stir for 5 minutes to obtain the second intermediate. The average particle size of the second intermediate is 11.50 μm (i.e., the average particle size of the second intermediate is 81 / 100 of the target average particle size of the ternary cathode active material).

[0165] (3) Prepare a mixed salt solution a2 (i.e., the third raw material solution) comprising nickel sulfate, cobalt sulfate, manganese sulfate, and strontium nitrate as a second dopant element. The total concentration of Ni, Co, and Mn metal ions in the mixed salt solution a2 is 2 mol / L, the molar ratio of Ni, Co, and Mn is 67:10:23 (i.e., the molar concentration of nickel is 1.34 mol / L), and the concentration of strontium is 0.2 mol / L. Introduce the mixed salt solution a2 into the reactor and adjust the pH of the system to 12.7 using 8 mol / L sodium hydroxide. Keep other parameters unchanged and proceed with the third coprecipitation reaction. Stop feeding when the size reaches the target value, and continue heating and low-intensity stirring (300 rpm) for 12 hours to ensure the third coprecipitation reaction proceeds fully. After the reaction is complete, release the liquid to obtain the third precipitate. The third precipitate was washed three times with ammonia water at pH 10. The filter cake was then dried in a vacuum drying oven at 120°C for 18 hours to obtain the dried ternary cathode active material precursor powder, with the general formula Ni. 0.6275 Co 0.1 Mn 0.27 W 0.0025 (OH)2@Ni 0.655 Co 0.1 Mn 0.23 Sr 0.015 (OH)2.

[0166] (4) The ternary cathode active material precursor powder is first sintered at 500℃ for 3 hours to obtain the first sintered product; the first sintered product is mixed with a portion of lithium carbonate and sintered at 550℃ for 2 hours to obtain the second sintered product; the second sintered product is mixed with the remaining lithium carbonate and sintered at 915℃ for 12 hours to obtain the ternary cathode active material. Among them, the molar ratio of lithium element mass to TM in the total lithium carbonate is 1.05, and TM is the sum of the molar amounts of the above-mentioned Ni, Co, and Mn elements; the mass ratio of the portion of lithium carbonate to the remaining lithium carbonate is 60:40.

[0167] Example 2

[0168] This embodiment is basically the same as Embodiment 1, except that:

[0169] (2) Stop the flow of the mixed solution after 4 minutes.

[0170] Example 3

[0171] This embodiment is basically the same as Embodiment 1, except that:

[0172] (2) Stop the flow of the mixed solution after 1.5 min.

[0173] Example 4

[0174] This embodiment is basically the same as Embodiment 1, except that:

[0175] (2) Stop the flow of the mixed solution after 6 minutes.

[0176] Example 5

[0177] This embodiment is basically the same as Embodiment 1, except that:

[0178] (2) Stop the flow of the mixed solution after 1 minute.

[0179] Example 6

[0180] This embodiment is basically the same as Embodiment 1, except that:

[0181] In the mixed salt solution a1, the concentration of tungsten is 0.01 mol / L.

[0182] (3) The obtained ternary cathode active material precursor powder has the general formula Ni 0.629 Co 0.1 Mn 0.27 W 0.001 (OH)2@Ni 0.655 Co 0.1 Mn 0.23 Sr 0.015 (OH)2.

[0183] Example 7

[0184] This embodiment is basically the same as Embodiment 1, except that:

[0185] In the mixed salt solution a1, the concentration of tungsten is 0.04 mol / L.

[0186] (3) The obtained ternary cathode active material precursor powder has the general formula Ni 0.627 Co 0.1 Mn 0.27 W 0.003 (OH)2@Ni 0.655 Co 0.1 Mn 0.23 Sr 0.015 (OH)2.

[0187] Example 8

[0188] This embodiment is basically the same as Embodiment 1, except that:

[0189] In the mixed salt solution a1, the concentration of tungsten is 0.05 mol / L.

[0190] (3) The obtained ternary cathode active material precursor powder has the general formula Ni 0.6255 Co 0.1 Mn 0.27 W 0.0045 (OH)2@Ni 0.655 Co 0.1 Mn 0.23 Sr 0.015 (OH)2.

[0191] Example 9

[0192] This embodiment is basically the same as Embodiment 1, except that:

[0193] In the mixed salt solution a2, the concentration of strontium is 0.08 mol / L.

[0194] (3) The obtained ternary cathode active material precursor powder has the general formula Ni 0.6275 Co 0.1 Mn 0.27 W 0.0025 (OH)2@Ni 0.665 Co 0.1 Mn 0.23 Sr 0.005 (OH)2.

[0195] Example 10

[0196] This embodiment is basically the same as Embodiment 1, except that:

[0197] In the mixed salt solution a2, the concentration of strontium is 0.3 mol / L.

[0198] (3) The obtained ternary cathode active material precursor powder has the general formula Ni 0.6275 Co 0.1 Mn 0.27 W 0.0025 (OH)2@Ni 0.65 Co 0.1 Mn 0.23 Sr 0.02 (OH)2.

[0199] Example 11

[0200] This embodiment is basically the same as Embodiment 1, except that:

[0201] In the mixed salt solution a2, the concentration of strontium is 0.35 mol / L.

[0202] (3) The obtained ternary cathode active material precursor powder has the general formula Ni 0.6275 Co 0.1 Mn 0.27 W 0.0025 (OH)2@Ni 0.645 Co 0.1 Mn 0.23 Sr 0.025 (OH)2.

[0203] Example 12

[0204] This embodiment is basically the same as Embodiment 1, except that:

[0205] (4) The ternary cathode active material precursor powder is first sintered at 600℃ for 5h to obtain the first sintered product.

[0206] Example 13

[0207] This embodiment is basically the same as Embodiment 1, except that:

[0208] In (4), the first sintered product is mixed with a portion of lithium carbonate and sintered at 600°C for 3 hours to obtain the second sintered product. The mass ratio of the portion of lithium carbonate to the remaining lithium carbonate is 50:50.

[0209] Example 14

[0210] This embodiment is basically the same as Embodiment 1, except that:

[0211] In the mixed salt solution a1, the first dopant element source is ammonium molybdate, and the concentration of molybdenum is 0.045 mol / L.

[0212] In the mixed salt solution a2, the second dopant element source is niobium sulfate, and the concentration of niobium is 0.06 mol / L.

[0213] The average particle size of the first intermediate is half that of the average particle size of the ternary cathode active material.

[0214] The general formula for ternary cathode active material precursor powder is Ni 0.626 Co 0.1 Mn 0.27 Mo 0.004 (OH)2@Ni 0.664 Co 0.1 Mn 0.23 Nb 0.006 (OH)2.

[0215] The second sintering product was mixed with the remaining lithium carbonate and sintered at 920°C for 15 hours to obtain a ternary cathode active material.

[0216] Example 15

[0217] This embodiment is basically the same as Embodiment 1, except that:

[0218] In the mixed salt solution a1, the first dopant element is ammonium molybdate, and the concentration of molybdenum is 0.032 mol / L.

[0219] In the mixed salt solution a2, the second dopant element is ammonium cerate, and the concentration of cerium is 0.1 mol / L.

[0220] The average particle size of the first intermediate is 7 / 10 of the average particle size of the ternary cathode active material.

[0221] The general formula for ternary cathode active material precursor powder is Ni 0.6272 Co 0.1 Mn 0.27 Mo 0.0028 (OH)2@Ni 0.66 Co 0.1 Mn 0.23 Ce 0.01 (OH)2.

[0222] The second sintering product was mixed with the remaining lithium carbonate and sintered at 905°C for 10 hours to obtain a ternary cathode active material.

[0223] Example 16

[0224] This embodiment is basically the same as Embodiment 1, except that:

[0225] In the mixed salt solution a1, the concentration of tungsten is 0.06 mol / L.

[0226] In the mixed salt solution a2, the concentration of strontium is 0.35 mol / L.

[0227] (3) The obtained ternary cathode active material precursor powder has the general formula Ni 0.625 Co 0.1 Mn 0.27 W 0.005 (OH)2@Ni 0.645 Co 0.1 Mn 0.23 Sr 0.025 (OH)2.

[0228] Example 17

[0229] This embodiment is basically the same as Embodiment 1, except that:

[0230] In the mixed salt solution a1, the concentration of tungsten is 0.1 mol / L.

[0231] In the mixed salt solution a2, the concentration of strontium is 0.08 mol / L.

[0232] (3) The obtained ternary cathode active material precursor powder has the general formula Ni 0.625 Co 0.1 Mn 0.27 W 0.006 (OH)2@Ni 0.666 Co 0.1 Mn 0.23 Sr 0.004 (OH)2.

[0233] Example 18

[0234] This embodiment is basically the same as Embodiment 1, except that:

[0235] In the mixed salt solution a1, the molar concentration of nickel is 1.56 mol / L. The first dopant element is ammonium tantalum oxalate.

[0236] In mixed salt solution a2, the molar concentration of nickel is 1.62 mol / L. The second dopant element in mixed salt solution a2 is ammonium zirconate.

[0237] (3) The obtained ternary cathode active material precursor powder has the general formula Ni 0.7775 Co 0.1 Mn 0.12 Ta 0.0025 (OH)2@Ni 0.805 Co 0.1 Mn 0.09 Zr 0.005 (OH)2.

[0238] (4) The second sintering product was mixed with the remaining lithium carbonate and sintered at 810°C for 13 hours to obtain a ternary cathode active material.

[0239] Example 19

[0240] This embodiment is basically the same as Embodiment 1, except that:

[0241] The first sintered product, lithium fluoride, and a portion of lithium carbonate were mixed and sintered at 550°C for 2 hours to obtain the second sintered product. Lithium fluoride was added at a concentration of 200 ppm of phosphorus.

[0242] Example 20

[0243] This embodiment is basically the same as Embodiment 1, except that:

[0244] The first sintered product was mixed with a portion of lithium carbonate, and then subjected to a second sintering at 650°C for 2 hours to obtain the second sintered product. The mass ratio of the portion of lithium carbonate to the remaining lithium carbonate was 30:70.

[0245] Example 21

[0246] This embodiment is basically the same as Embodiment 1, except that:

[0247] In the mixed salt solution a1, the concentration of tungsten is 0.09 mol / L.

[0248] (3) The obtained ternary cathode active material precursor powder has the general formula Ni 0.6225 Co 0.1 Mn 0.27 W 0.0075 (OH)2@Ni 0.655 Co 0.1 Mn 0.23 Sr 0.015 (OH)2.

[0249] Example 22

[0250] This embodiment is basically the same as Embodiment 1, except that:

[0251] (1) The total concentration of Ni, Co and Mn metal ions in the mixed salt solution a1 is 1.5 mol / L. R1 / R0 = 3 / 4.

[0252] (3) The total concentration of Ni, Co and Mn metal ions in the mixed salt solution a2 is 1.5 mol / L.

[0253] (4) The ternary cathode active material precursor powder is first sintered at 400°C for 2 hours to obtain the first sintered product; the first sintered product is mixed with a portion of lithium carbonate and sintered at 500°C for 1 hour to obtain the second sintered product; the second sintered product is mixed with the remaining lithium carbonate and sintered at 700°C for 8 hours.

[0254] Example 23

[0255] This embodiment is basically the same as Embodiment 1, except that:

[0256] (1) The total concentration of Ni, Co and Mn metal ions in the mixed salt solution a1 is 2.5 mol / L. R1 / R0 = 3 / 4.

[0257] (3) The total concentration of Ni, Co and Mn metal ions in the mixed salt solution a2 is 2.5 mol / L.

[0258] (4) The ternary cathode active material precursor powder is first sintered at 600°C for 5 hours to obtain the first sintered product; the first sintered product is mixed with a portion of lithium carbonate and sintered at 700°C for 3 hours to obtain the second sintered product; the second sintered product is mixed with the remaining lithium carbonate and sintered at 950°C for 25 hours.

[0259] Comparative Example 1

[0260] This comparative example is basically the same as Example 1, except that:

[0261] Without performing step (2), after obtaining the first intermediate, proceed directly to step (3) to obtain the ternary cathode active material precursor powder.

[0262] The obtained ternary cathode active material precursor powder was mixed with lithium carbonate and sintered at 920℃ for 12 h to obtain the ternary cathode active material. The molar ratio of lithium element mass to TM in the total lithium carbonate was 1.05, where TM is the sum of the molar amounts of Ni, Co, and Mn elements.

[0263] Comparative Example 2

[0264] This comparative example is basically the same as Example 1, except that:

[0265] The average particle size of the first intermediate is 2 / 5 of the target average particle size of the ternary cathode active material.

[0266] (3) The obtained ternary cathode active material precursor powder has the general formula Ni 0.625 Co 0.1 Mn 0.27 W 0.005 (OH)2@Ni 0.6625 Co 0.1 Mn 0.23 Sr 0.0075 (OH)2.

[0267] Comparative Example 3

[0268] This comparative example is basically the same as Example 1, except that:

[0269] The average particle size of the first intermediate is 9 / 10 of the target average particle size of the ternary cathode active material.

[0270] (3) The obtained ternary cathode active material precursor powder has the general formula Ni 0.628 Co 0.1 Mn 0.27 W 0.002 (OH)2@Ni 0.645 Co 0.1 Mn 0.23 Sr0.025 (OH)2.

[0271] Experimental Example 1

[0272] 1. The general formula of the ternary cathode active materials prepared in the examples and comparative examples is shown in Table 1A, and the preparation conditions are shown in Tables 1B and 1C. The inner and outer layers of the ternary cathode active materials in the examples and comparative examples were tested for the type of doping element, the average particle size (abbreviated as average particle size), the average aspect ratio (abbreviated as aspect ratio), and the average porosity (abbreviated as porosity), and the results are shown in Table 2A. The average porosity (abbreviated as total porosity), particle strength, inner layer radius, the ratio of the inner layer radius to the radius of the ternary cathode active material, and the thickness of the cross-layer were tested for the ternary cathode active materials in the examples and comparative examples, and the results are shown in Table 2B.

[0273] Depend on Figure 1 , Figure 2 It can be seen that the ternary positive electrode active materials prepared in Examples 1 and 22 of the present invention have an interlaced layer; by Figure 3 It can be seen that the thickness of the interlaced layer of the ternary cathode active material prepared in Example 1 is 280 μm.

[0274] 2. Testing Methods

[0275] 1) Test methods for the types of doped elements in the inner and outer layers

[0276] Using a Shimadzu electron probe X-ray micro-area analyzer (EPMA-1720), the ternary cathode active materials prepared in the examples and comparative examples were first processed by an ion mill cross-section profiler, and then the elemental composition of individual particles was comprehensively scanned.

[0277] 2) Test methods for the average particle size and average aspect ratio of the inner and outer primary particles.

[0278] The cross-section of the ternary cathode active material was obtained using a Hitachi IM4000Ⅱ ion milling machine. The cross-section was imaged using an S-4800 scanning electron microscope, and the inner primary particles were tested using Nano Measurer software.

[0279] For each secondary particle profile, the primary particles located in the inner layer region are measured using their geometric center as the center. In the two-dimensional image obtained by scanning electron microscopy (SEM), a rectangle with the smallest area that completely encloses the projection of the inner primary particle is identified. The longer side of this rectangle is defined as the length of the inner primary particle, and the shorter side as its width. The aspect ratio of a single inner primary particle is then calculated. The average diameter of all primary particles within the same particle is obtained by averaging the measurements. The average diameter of the outer primary particles is determined using the same method, but measurements are taken from the primary particles in the outer layer region of the secondary particles. At least five different secondary particles are measured for each sample, and the final average diameters of the inner and outer primary particles are the average of these measurements.

[0280] The aspect ratio is calculated as the ratio of the radial length of a primary particle to its width perpendicular to the radial direction, and the average value is taken.

[0281] 3) Test methods for the porosity of inner primary particles, outer primary particles, and ternary cathode active materials.

[0282] The cross-section of the ternary cathode active material was obtained using a Hitachi IM4000Ⅱ ion mill. Images of the material cross-section were sampled using an S-4800 scanning electron microscope, and image contrast analysis was performed using the LIBMAS intelligent image analysis system to obtain the porosity of the inner and outer primary particles and the ternary cathode active material. The test value for each sample was the average porosity measured using six particle spheres. Samples with cross-sectional diameters between D50 and D80 of the material particle size were selected when photographing the samples using the S-4800 scanning electron microscope. Simultaneously, the inner and outer layer regions were manually identified to avoid discrepancies in porosity.

[0283] 4) Test method for particle strength

[0284] The particle strength of the ternary cathode active material was measured using a dynamic ultra-microhardness tester (model: DUH-211S). Each sample was measured 15 times and the average value was taken.

[0285] 5) Test methods for the radius of the inner layer and the ratio of the inner layer radius to the radius of the ternary cathode active material.

[0286] The contour of the secondary particles is fitted using image processing software to calculate the circumcircle (or quasi-circumcircle) of the particle contour. The center of this circumcircle is the sphere center C. Alternatively, for irregular quasi-spherical particles in actual production, the sphere center C can be obtained by measuring the longest and shortest diameters of the particles and taking the intersection of the lines connecting the midpoints of the two diameters. R0 refers to the maximum distance from the sphere center C to the particle surface, which is the radius of the aforementioned circumcircle (or half of the longest diameter). The radius can be obtained, for example, by testing with a particle size analyzer. R1 refers to the distance from the secondary particle center C to the interface between the inner layer and the cross-layer.

[0287] 6) Test methods for cross-layer thickness and outer layer thickness

[0288] The sample to be tested was dried in a vacuum oven at 100°C for 24 hours. Then, the distribution of dopant elements in the material was measured using X-ray energy dispersive spectroscopy (EDS) in a transmission electron microscope (TEM) to obtain the variation of dopant elements. The variation was confirmed by the element distribution lines of the inner and outer layers. The thickness of the layer where the element content is interlaced is the thickness of the interlaced layer, and the thickness of the outer layer where there is only a second dopant element source is the thickness of the outer layer. At least 5 different secondary particles (or different edge positions of the same particle) were randomly selected, and the above steps were repeated, and the average value was taken.

[0289] Table 1A

[0290]

[0291] Table 1B

[0292]

[0293] Table 1C

[0294]

[0295] Table 2A

[0296]

[0297] Table 2B

[0298]

[0299] Experimental Example 2

[0300] 1. The ternary cathode active materials prepared in the above examples and comparative examples were used to prepare coin cells and pouch cells. Capacity retention rate test, capacity test, storage recovery performance test and rate performance test were conducted. The test results are shown in Table 3.

[0301] Methods for manufacturing button cells:

[0302] (1) A ternary cathode active material is prepared into a cathode sheet, which is then stacked sequentially with a separator and a cathode sheet to obtain a secondary battery. Specifically, each ternary cathode active material is mixed with conductive carbon black (SP) and PVDF in a weight ratio of 95%:3%:2%, and dispersed to obtain a cathode slurry. The cathode slurry is coated onto an aluminum foil current collector, dried in a 120°C oven for 30 min, and then rolled to obtain a cathode sheet with a compaction density of 3.4 g / cm³. 3 .

[0303] (2) In a glove box under an Ar protective atmosphere, a 2430 button cell case is used, and an electrolyte is made of LiPF6, EC (ethylene carbonate), EMC and DEC to assemble a 2430 button cell; wherein, the content of LiPF6 is 1 mol / L, and the volume ratio of EC, EMC and DEC is 1:1:1.

[0304] Methods for manufacturing pouch cells:

[0305] 1) The ternary positive electrode active material, conductive carbon black, and binder polyvinylidene fluoride (PVDF) are mixed evenly in N-methylpyrrolidone solvent at a mass ratio of 95:3:2 to obtain a positive electrode slurry. The positive electrode slurry is coated on aluminum foil, and after drying and cold pressing, a positive electrode sheet containing a positive electrode active layer with a thickness of 100μm is obtained.

[0306] 2) Mix artificial graphite anode material, conductive carbon black (SP), sodium carboxymethyl cellulose binder (CMC) and styrene-butadiene rubber (SBR) in a mass ratio of 96:1:1.5:1.5, add deionized water as solvent, and stir thoroughly to form a uniform anode slurry; coat the anode slurry uniformly on the surface of copper foil current collector, dry it and then cold press it to obtain anode sheet (active layer thickness of about 100μm).

[0307] 3) The electrolyte includes ethylene carbonate (EC), ethyl methyl carbonate (EMC), and LiPF6. The volume ratio of ethylene carbonate (EC) to ethyl methyl carbonate (EMC) is 3:7, and the mass percentage of LiPF6 in the electrolyte is 12.5%. The diaphragm is a PE-based diaphragm.

[0308] 4) Stack the positive electrode sheet, separator, negative electrode sheet, and separator in sequence, repeating the stacking process up to 20 layers. Lead out the positive and negative electrode tabs in opposite directions to obtain a stacked cell. Place the stacked cell into an aluminum-plastic composite film packaging bag for heat sealing and inject the aforementioned electrolyte to obtain a pouch battery.

[0309] 2. Testing Method:

[0310] 1) Rate performance test: The prepared soft-pack battery was tested for charge and discharge rate at 25℃ using a battery charge and discharge tester. The charge and discharge rate regime was as follows: constant current charging at 0.2C to 4.25V, then constant voltage charging at 4.25V until the current decreased to 0.02C, and after standing for 5 minutes, constant current discharging at 0.2C to 2.5V. The discharge capacity Q was recorded. 0.2c After resting for 5 minutes, charge with a constant current of 0.2C to 4.25V, then switch to a constant voltage of 4.25V and charge until the current decreases to 0.02C. After resting for 5 minutes, discharge with a constant current of 2C to 2.5V, and record the discharge capacity Q. 2c The capacity retention rate can be calculated using the following formula:

[0311] 2C discharge rate capacity retention rate = Q 2c / Q 0.2c ×100%.

[0312] 2) Capacity retention test

[0313] The prepared pouch cell was charged at 45°C with a constant current of 1C to 4.50V, then charged at a constant voltage of 0.05C to 4.50V, and then discharged at a discharge rate of 1C to 3.0V. This charge-discharge cycle was repeated 300 times. The discharge capacity Q1 at the first cycle and the discharge capacity Q at the 300th cycle were measured. 300 .

[0314] The capacity retention rate Q after 300 cycles is calculated using the following formula. 300 .

[0315] Capacity retention rate Q = Q 300 / Q1*100%.

[0316] 3) Storage performance test:

[0317] The prepared pouch battery was placed at room temperature (25°C) and charged at a constant current rate of 1C to 4.50V, then charged at a constant voltage rate of 0.05C to 4.50V, and finally discharged at a discharge rate of 1C to 3.0V. The 1C discharge capacity Q was recorded. The fully charged battery was stored at 60°C for 28 days, and the 1C discharge capacity Q1 after 28 days was recorded. Then, the battery was charged at room temperature (25°C) at a constant current rate of 1C to 4.50V, then charged at a constant voltage rate of 0.05C to 4.50V, and finally discharged at a discharge rate of 1C to 3.0V. The discharge capacity Q2 was recorded. The capacity recovery rate of the battery after high-temperature storage was calculated using the following formula.

[0318] High-temperature capacity recovery rate (%) = Q2 / Q × 100%.

[0319] 4) 0.33C Capacity Test:

[0320] The prepared button cell is charged at a constant current rate of 0.33C until the voltage reaches the cutoff voltage (4.25V for series 8 and above, and 4.3V for series 7). Then, it is charged at a constant voltage under the cutoff voltage condition until the current is less than 0.05C. The charging capacity at this time is recorded as the first charge capacity. After resting for 5 minutes, it is discharged at a constant current rate of 0.33C until the voltage reaches 2.5V. The discharge capacity at this time is recorded as the battery's first discharge specific capacity, which is the 0.33C capacity.

[0321] Table 3

[0322]

[0323] As shown in Table 3, compared with the comparative example, the secondary battery made of the ternary cathode active material of the present invention has excellent rate performance, cycle performance, and storage performance.

[0324] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A ternary cathode active material, characterized in that, The secondary particles include spherical or near-spherical particles, each secondary particle comprising an inner layer and an outer layer covering at least a portion of the surface of the inner layer. The inner layer comprises a plurality of inner primary particles, and the outer layer comprises a plurality of outer primary particles. The average particle size of the inner primary particles is smaller than the average particle size of the outer primary particles. Some of the inner primary particles and some of the outer primary particles interweave at the interface to form an interleaved layer. R1 / R0 = 1 / 2 - 4 / 5; where the center of the secondary particle is C and the radius is R0; in the secondary particle, with C as the center, R1 is the radius of the inner layer.

2. The ternary cathode active material according to claim 1, characterized in that, The R1 / R0 = 7 / 10 - 4 / 5; and / or, The average aspect ratio a of the inner primary particles is ≥1.8, preferably 2≤a≤3; and / or, The average aspect ratio b of the outer primary particles is ≤2, preferably 1.2 ≤ b ≤ 1.7; and / or, The average particle size of the inner layer primary particles is 150-350 nm, preferably 180-300 nm; and / or, The average particle size of the outer primary particles is 200-450 nm, preferably 250-400 nm.

3. The ternary cathode active material according to claim 1 or 2, characterized in that, The thickness of the interlaced layer is 50-500 nm, preferably 100-300 nm.

4. The ternary cathode active material according to any one of claims 1-3, characterized in that, The average porosity of the inner layer is less than the average porosity of the outer layer; and / or, the average porosity of the ternary cathode active material is <0.5%.

5. The ternary cathode active material according to any one of claims 1-4, characterized in that, The average particle size of the ternary cathode active material is 10-16 μm; and / or, The average porosity of the inner layer is 0.1-0.75%; and / or, The average porosity of the outer layer is 0.36-1.78%.

6. The ternary cathode active material according to any one of claims 1-5, characterized in that, The general formula of the ternary cathode active material is Li 1+a [Ni x Co y Mn z M1 m M2 n O 2±c A d Where 0.6 ≤ x < 1, 0 <y<0.3,0<z<0.3,0<a<0.2,c<0.02,0≤d≤0.05,x+y+z+m+n=1,0.0005≤m≤0.005,0.0005≤n≤0.005; M1 includes at least one of W, Mo, and Ta; M2 includes at least one of Zr, Sr, Nb, and Ce; and A includes at least one of F and S.

7. A method for preparing a ternary cathode active material according to any one of claims 1-6, characterized in that, Includes the following steps: Under alkaline conditions, a first coprecipitation reaction is carried out using a first raw material solution including a metal source and a first dopant element source to obtain a first intermediate; a second coprecipitation reaction is carried out using a second raw material solution including the metal source and the first intermediate to obtain a second intermediate; a third coprecipitation reaction is carried out using a third raw material solution including the metal source, the second intermediate, and a second dopant element source to obtain a ternary cathode active material precursor; wherein, the average particle size of the first intermediate is 1 / 2 to 4 / 5 of the target average particle size of the ternary cathode active material; The ternary cathode active material is obtained by sintering a mixed raw material comprising the ternary cathode active material precursor and a lithium source. The first doping element source includes at least one of W source, Mo source, and Ta source. The second doping element source includes at least one of Zr source, Sr source, Nb source, and Ce source.

8. The preparation method according to claim 7, characterized in that, The concentration of the metal source in the first raw material solution is 1.5-2.5 mol / L; and / or, The concentration of the metal source in the third raw material solution is 1.5-2.5 mol / L; and / or, The molar concentration of the first dopant source is less than the molar concentration of the second dopant source; and / or, The metal source includes a nickel source, and the molar concentration of the nickel source in the third raw material solution is greater than the molar concentration of the nickel source in the first raw material solution; and / or, The average particle size of the second intermediate is 13 / 25-17 / 20 of the target average particle size of the ternary cathode active material; and / or, The sintering process specifically includes the following steps: the ternary cathode active material precursor is sintered at 400-600℃ for 2-5 hours to obtain a first sintered product; the first sintered product is mixed with a portion of lithium salt and then sintered at 500-700℃ for 1-3 hours to obtain a second sintered product; the second sintered product is mixed with the remaining lithium salt and then sintered at 700-950℃ for 8-25 hours to obtain the ternary cathode active material; wherein the mass ratio of the portion of lithium salt to the remaining lithium salt is (30-60):(70-40), preferably (50-60):(50-40).

9. A positive electrode plate, characterized in that, It includes the ternary cathode active material according to any one of claims 1-6, or the ternary cathode active material prepared by the preparation method according to claim 7 or 8.

10. A secondary battery, characterized in that, It includes the ternary positive electrode active material according to any one of claims 1-6, or the ternary positive electrode active material prepared by the preparation method according to claim 7 or 8, or the positive electrode sheet according to claim 9.

Images