Positive electrode active material, preparation method thereof and battery

Abstract

The invention discloses a positive electrode active material, a preparation method thereof and a battery, the positive electrode active material comprises single crystal particles, the positive electrode active material comprises a nickel-cobalt-manganese ternary material, and the long-range order degree eta of the positive electrode active material is 0.85-0.96; wherein,; dS is the average size of the single crystal particles; dx is the sub-grain average size of a single long-range ordered crystal calculated in an X-ray diffraction refinement diagram of the positive electrode active material. Therefore, the positive electrode active material is good in internal crystallinity, consistent in arrangement direction and low in cation disorder degree, the impedance of the positive electrode active material can be reduced, and the capacity exertion and rate capability of the positive electrode active material can be improved; and more importantly, the lithium ion diffusion kinetics can be improved, the heterogeneous reaction can be inhibited, the local lattice anisotropic strain in the charging and discharging process can be further relieved, the micro-crack generation risk can be reduced, and the cycling stability of the positive electrode active material can be obviously improved.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, specifically to positive electrode active materials and their preparation methods, and batteries. Background Technology

[0002] With the booming development of the new energy vehicle industry and the continuous upgrading of power battery technology, higher requirements have been placed on the performance of cathode active materials. Developing high-performance cathode active materials has become the key to promoting industry progress. Among various technical routes, single-crystal ternary materials have gradually become a research and development hotspot due to their high particle strength, high specific capacity, excellent thermal stability and cycle performance.

[0003] Monocrystalline ternary materials possess a complete structure, high particle strength, and high compaction density, avoiding the grain boundary and particle stacking problems commonly found in traditional secondary particles. This not only helps achieve better capacity utilization but also significantly reduces microcracks and pulverization of the cathode active material during cycling, thereby improving battery cycle life. Simultaneously, monocrystalline ternary materials have a smaller specific surface area and lower porosity, offering advantages in suppressing gas generation, thermal stability, and high-temperature cycling performance. However, despite their good structural stability, monocrystalline ternary materials are still susceptible to complex failure modes under high SOC and high voltage conditions.

[0004] It should be noted that the above statements are only used to provide background information related to this application and do not necessarily constitute prior art. Summary of the Invention

[0005] In a first aspect, this application proposes a positive electrode active material, wherein the positive electrode active material comprises single crystal particles, the positive electrode active material comprises a nickel-cobalt-manganese ternary material, and the long-range order η of the positive electrode active material is 0.85~0.96; wherein, ;D S D represents the average size of the single crystal particles; x The average subgrain size of a single long-range ordered crystal, calculated from the refined X-ray diffraction pattern of the cathode active material. This results in good internal crystallinity, consistent cation orientation, and low cation disorder in the cathode active material, which helps reduce its impedance, improve its capacity utilization and rate performance. More importantly, it improves lithium-ion diffusion kinetics and suppresses heterogeneous reactions, further mitigating localized anisotropic strain during charge and discharge, reducing the risk of microcrack formation, and significantly enhancing the cycle stability of the cathode active material.

[0006] In some embodiments, the long-range order η of the positive electrode active material is 0.88~0.93. This is beneficial for further eliminating dislocations and subgrain boundaries within the crystal of the positive electrode active material, thereby improving structural and electrochemical stability.

[0007] In some embodiments, 0.8 μm ≤ D s ≤1.8μm; 0.7μm≤D x ≤1.7μm. This is beneficial for improving the long-range order of the positive electrode active material, reducing structural distortion, and improving the rate performance of the positive electrode active material.

[0008] In some embodiments, the cation order degree μ of the positive electrode active material is 95%~99%; optionally, 95.5%~98.5%; wherein, n(Nio) represents the number of Ni atoms mixed at Li sites in the positive electrode active material, and n(Nim) represents the total number of Ni atoms in the lattice of the positive electrode active material. This helps to reduce the kinetic energy barrier during lithium-ion insertion and extraction, thereby improving the battery's rate performance and low-temperature discharge capability. Secondly, it helps to reduce the lattice mismatch between the transition metal layer and the lithium layer, reducing the anisotropic stress inside the positive electrode active material during repeated charge and discharge, effectively suppressing lattice slip and intracrystalline crack formation, reducing side reactions caused by continuous exposure of fresh surfaces to the electrolyte, and thus improving the structural integrity and interface stability of single crystal particles during cycling. Furthermore, the high order of cations can reduce local crystal field disturbances caused by lithium-nickel antisite defects, stabilize the redox potential of the positive electrode active material, contribute to a stable voltage plateau, and improve battery life.

[0009] In some embodiments, the equivalent number of lamellar layers N of the positive electrode active material (003) crystal plane is... (003) The effective number of lamellar layers N of the positive electrode active material (104) crystal plane is 160~240. (104) The range is 250-400; among which, D (003) The average thickness of the positive electrode active material in the unit cell perpendicular to the (003) crystal plane is expressed in nm. (003) The interplanar spacing of the (003) crystal plane in the unit cell of the positive electrode active material is expressed in nm. D (104) The average thickness of the positive electrode active material in the unit cell perpendicular to the (104) crystal plane is expressed in nm and d. (104) The interplanar spacing of the (104) crystal plane in the unit cell of the positive electrode active material is expressed in nm.

[0010] When the equivalent number of lamellar layers of the (003) crystal plane and the (104) crystal plane of the positive electrode active material are within the above range, the Li-C100 is further improved. +Diffusion kinetics reduces the solid-phase migration path of lithium ions during in-layer insertion and extraction, thus improving the rate performance of the material. An appropriate number of crystal lamellae ensures the particle size of the material. An excessive number of crystal lamellae increases the difficulty of atomic orderly stacking and reduces the intracrystalline order. In addition, an appropriate number of equivalent crystal lamellae has a stabilizing effect on the expansion and contraction of the c-axis of the cathode active material lattice during charging and discharging. This can alleviate material structural distortion and collapse, suppress heterogeneous reactions inside and outside the single crystal caused by excessive single crystal size, and improve the cycle stability of the cathode active material.

[0011] In some embodiments, the positive electrode active material satisfies the chemical formula: Li 1+a Ni u Co v Mn w M m J n O 2+b Wherein, -0.05≤a≤0.3, 0.8≤u≤1, 0≤v≤0.2, 0≤w≤0.2, 0<m≤0.02, 0≤n≤4, -0.05≤b≤0.3; element M includes at least one of Zr, Al, Ce, Ba, Mg, and Sr; element J includes at least one of Al, Zr, F, B, Cl, Br, I, S, W, La, and P. Therefore, by introducing dopant element M, the lattice parameters and long-range order of the cathode active material can be controlled, coordinating the balance between high density and fast ion diffusion channels, forming fast lithium-ion transport channels within the dense lattice, and significantly improving the rate performance of the cathode active material. Furthermore, by doping with element M, slightly different heterostructures can be constructed on the surface and near the surface of the cathode active material compared to the interior, suppressing lattice distortion and irreversible phase transitions during deep delithiation, alleviating differences in electrochemical reactions inside and outside the single crystal, reducing local stress and delamination risk, and improving electrochemical stability.

[0012] In some embodiments, the ratio of the molar amount of element M to the sum of the molar amounts of nickel, cobalt, and manganese, n(M) / n(Ni+Co+Mn), is greater than 0.005. Therefore, the doping amount of element M is moderate, which can stabilize the crystal lattice and suppress cracks using doped ions, while having a relatively small impact on specific capacity and lithium-ion diffusion rate.

[0013] In some embodiments, the molar amount of element M on the surface of the positive electrode active material is greater than the molar amount of element M inside the positive electrode active material. Therefore, by performing shallow surface doping on the positive electrode active material, a heterostructure with slight differences between the single-crystal surface and interior is constructed. Introducing more crystal orientations different from the interior onto the surface allows for effective suppression of interfacial side reactions by optimizing the surface chemical environment, while maintaining the stability of the main particle structure. This reduces electrolyte erosion and transition metal dissolution, while mitigating lattice strain and local stress concentration during cycling, reducing the difference in phase transitions between the surface and interior, lowering the risk of delamination, and inhibiting further erosion of the surface CEI into the interior, thereby significantly improving the cycle life of the positive electrode active material.

[0014] In a second aspect, this application proposes a method for preparing the aforementioned positive electrode active material, comprising: mixing a nickel source, a cobalt source, a manganese source, a precipitant, and a complexing agent, and then performing a co-precipitation reaction to obtain a precursor; mixing the precursor, a first lithium source, and a first M source, and then performing a first sintering treatment to obtain a first sintered material, wherein the molar amount of lithium corresponding to the first lithium source is in the ratio of the total molar amount of nickel, cobalt, and manganese in the precursor to 0.8~0.95; mixing the first sintered material and a second lithium source, and then performing a second sintering treatment to obtain a second sintered material, wherein the molar amount of lithium corresponding to the second lithium source is greater than the molar amount of lithium corresponding to the first lithium source; and mixing the second sintered material and the second M source, and then performing a third sintering treatment to obtain the positive electrode active material. This application effectively suppresses the formation of lattice defects and constructs a locally ordered superlattice structure by precisely controlling the amount of lithium source added during the first and second sintering treatments. Simultaneously, by doping with M element to construct a heterostructure on the surface of the positive electrode active material, it enhances structural stability. Moreover, the preparation method is simple, easy to operate, and easy to industrialize.

[0015] In some embodiments, the ratio of the sum of the molar amounts of lithium corresponding to the first lithium source and the second lithium source to the total molar amounts of nickel, cobalt, and manganese in the precursor is 1.02 to 1.10. Therefore, limiting the amount of the first lithium source helps suppress the formation of lattice defects in the positive electrode active material, constructing a locally ordered superlattice structure. Limiting the amount of the second lithium source provides precise lithium source replenishment for crystal growth, improving the integrity and uniformity of the crystal structure.

[0016] In some embodiments, the temperature of the first sintering treatment is 700℃~900℃, and the time is 6h~12h; and / or, the temperature of the second sintering treatment is 700℃~850℃, and the time is 6h~12h. This helps to reduce defects inside the positive electrode active material and form a complete crystal lattice structure.

[0017] In some embodiments, the molar amount of element M corresponding to the second M source is greater than the molar amount of element M corresponding to the first M source. This facilitates the construction of an internal and external heterogeneous structure on the surface of the positive electrode active material.

[0018] In some embodiments, the temperature of the third sintering treatment is 500℃~700℃, and the time is 3h~10h. Thus, element M can enter the surface structure of the single-crystal cathode active material in the form of single atoms or atomic clusters, realizing the construction of a surface heterostructure.

[0019] In some embodiments, the method further includes: mixing the positive electrode active material and the J source and then performing a fourth sintering treatment; wherein the temperature of the fourth sintering treatment is 200℃~500℃ and the time is 3h~10h. This facilitates the formation of a coating layer on the surface of the positive electrode active material, reduces the occurrence of side reactions between the positive electrode active material matrix and the electrolyte, and improves the cycle stability of the positive electrode active material.

[0020] In a third aspect of this application, a battery is provided, comprising a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer located on at least one side of the positive current collector, the positive active material layer comprising the positive active material described in the first aspect of this application or a positive active material prepared using the method described in the second aspect of this application. Therefore, the battery exhibits excellent rate performance and cycle stability. Attached Figure Description

[0021] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein, Figure 1 Here is a SEM image of the positive electrode active material according to an embodiment of this application; Figure 2 This is a cross-sectional SEM image of the positive electrode active material according to an embodiment of this application. Detailed Implementation

[0022] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0023] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0024] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0025] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0026] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0027] In the description of this application, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. "First feature" and "second feature" may include one or more of that feature.

[0028] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0029] In this application, the order in which the steps are written does not imply a strict execution order and does not limit the implementation process. The specific execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps in this application can be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0030] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0031] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0032] Single-crystal materials have long diffusion paths, which easily lead to uneven lithium concentration gradients. Electrochemical reactions under high voltage or high SOC can trigger severe asynchronous phase transitions on the single-crystal surface and inside. Taking layered oxide ternary materials as an example, this asynchronous phase transition causes the particles to separate into a lithium-poor and O1-rich surface phase and a lithium-rich and O3-rich bulk phase, resulting in local lattice strain, leading to particle degradation, premature capacity decay, and enhanced polarization.

[0033] In a first aspect, this application proposes a positive electrode active material, wherein the positive electrode active material comprises single crystal particles, the positive electrode active material comprises a nickel-cobalt-manganese ternary material, and the long-range order η of the positive electrode active material is 0.85~0.96; wherein, ;D S D represents the average size of the single crystal particles; x The average subgrain size of a single long-range ordered crystal is calculated from the refined X-ray diffraction pattern of the positive electrode active material.

[0034] As an example, the long-range order η of the positive electrode active material can be 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95 or 0.96, etc.

[0035] For single-crystal materials, D x The size of the "coherent scattering domain" represents the size of the region in a crystal where atoms are highly ordered and defect-free (e.g., grain boundaries, dislocations, twins). It reflects the long-range ordered crystallization quality of the material; D S Represents the macroscopic physical size of the particles. In single-crystal materials, a single particle is typically considered an independent crystal. Therefore, the long-range order η of a single-crystal material reflects how close the size of the ordered subgrains in the fabricated single crystal is to the actual particle size. An η value within the aforementioned range means that each physical particle is closer to a highly intact single crystal with regular internal orientation, almost no subgrain boundaries or severe structural distortions. This fundamentally reduces particle cracking and fragmentation caused by internal grain boundary slip or anisotropic stress during electrochemical processes, thus slowing down capacity decay.

[0036] In this application, the long-range order η of the positive electrode active material is within a suitable range, the internal crystallinity of the positive electrode active material is good, the arrangement direction is consistent, and the cation disorder is low, which helps to reduce the impedance of the positive electrode active material, ensure the capacity utilization and rate performance of the positive electrode active material; more importantly, it is beneficial to improve the lithium-ion diffusion kinetics and suppress heterogeneous reactions, further alleviate the local lattice anisotropic strain during the charging and discharging process, reduce the risk of microcrack formation, and significantly improve the cycle stability of the positive electrode active material.

[0037] If the value of η is too large, the structure of the positive electrode active material will be too rigid, which will make it unable to buffer anisotropic volume changes during high-voltage cycling, leading to concentrated initiation of microcracks and aggravation of interfacial side reactions, which will reduce the cycling stability.

[0038] If the η value is too small, the internal arrangement of the positive electrode active material is disordered, which not only directly reduces the active lithium sites that can be inserted and removed, causing a significant decrease in reversible capacity and first coulombic efficiency, but also severely blocks the lithium ion transport path, causing the rate performance to deteriorate. In addition, it also destroys the integrity of the layered structure, making it easier to induce violent phase transitions and lattice oxygen release during charging and discharging, leading to rapid structural collapse and a sharp deterioration in thermal stability.

[0039] As an example, D S The specific testing method includes: capturing sample morphology at 3K magnification using SEM; performing contrast analysis on the electron microscope images using the LIBMAS intelligent image analysis system to determine the area of ​​individual particles in the images; identifying circles with the same area as individual particles as equivalent circles; and calculating the average diameter of these circles, which is the average size of the single-crystal particles. For each sample, 10 3K images were analyzed, resulting in the average size of approximately 800–1500 single-crystal particles.

[0040] D xThe specific testing methods include: conducting X-ray diffraction tests on single-crystal positive electrode active materials with a 2θ1 range of 10° to 80° to obtain the full XRD spectrum; performing Rietveld refinement calculations on the full XRD spectrum to obtain the grain size in which long-range ordered diffraction can occur in the c-axis and a-axis directions; calculating the volume; and considering the particles as spheres to obtain the subgrain size of the average "coherent scattering domain" of the material.

[0041] XRD testing conditions: The XRD pattern was obtained using a Rigaku powder X-ray diffractometer (Smart Lab 9kW) after fine-tuning. The Cu target wavelength was 1.5418462 Å, tube voltage was 40 kV, tube current was 200 mA, scanning speed was 5 Hz / min, and the scanning range was 10–90 Å. A one-dimensional detector (1D) was used. Specific testing conditions were: operating temperature: 21 ± 5 °C, humidity: <65%; cooling water circulator: temperature: 23 ± 1 °C, water pressure: 0.36 MPa; high-pressure refrigerant: 0.8 MPa–1.8 MPa, low-pressure refrigerant: 0.4 MPa–0.7 MPa; step size: 0.0200 °C.

[0042] In some embodiments, the long-range order η of the positive electrode active material is 0.88~0.93. This is beneficial for further eliminating dislocations and subgrain boundaries within the crystal of the positive electrode active material, thereby improving structural and electrochemical stability.

[0043] In some embodiments, 0.8 μm ≤ D s ≤1.8μm, for example, it can be 0.8μm, 1.0μm, 1.2μm, 1.4μm, 1.6μm or 1.8μm, etc.; 0.7μm≤D x ≤1.7μm, for example, it can be 0.7μm, 0.9μm, 1.1μm, 1.3μm, 1.5μm, or 1.7μm, etc. This is beneficial for improving the long-range order of the positive electrode active material, reducing structural distortion, and improving the rate performance of the positive electrode active material. Specifically: An excessively large Ds indicates that during the growth process, a single particle is formed by the fusion of multiple precursor fibers. Dislocations and anisotropic alignment are easily formed at the fusion interface, reducing the long-range order within the single crystal phase. In addition, the large size of the single crystal particles results in an excessively long path for lithium ions to diffuse from the particle surface to the core, limiting diffusion kinetics and deteriorating rate performance and low-temperature performance. At the same time, the internal stress generated by the anisotropic volume change during the charging and discharging process of large-sized single crystal particles is difficult to release uniformly, making it easier for microcracks to initiate inside the grain. As the cycle progresses, the cracks propagate, ultimately leading to rapid capacity decay.

[0044] When the density (Ds) is too small, it is easier to form ordered individual particles within a single crystal. However, the smaller particle size makes crushing difficult and reduces the compaction density of the single crystal, affecting the volumetric energy density. The particles have poor dispersion and flowability, making it difficult to form uniform and dense electrodes during electrode coating, increasing the difficulty of electrode processing. In addition, the specific surface area of ​​a single crystal increases sharply when the size is too small, leading to an increase in side reaction sites with the electrolyte, exacerbating interfacial side reactions, and significantly reducing high-temperature storage and cycle life.

[0045] In some embodiments, the cation order degree μ of the positive electrode active material is 95%~99%; optionally, 95.5%~98.5%; wherein, n(Nio) is the number of Ni atoms mixed in the Li sites in the positive electrode active material, and n(Nim) is the total number of Ni atoms in the lattice of the positive electrode active material.

[0046] As an example, the cation order degree μ of the positive electrode active material can be 95%, 96%, 97%, 98%, or 99%, etc.

[0047] The essence of regulating the cation order in single-crystal cathode active materials lies in migrating transition metal ions (mainly nickel) from the lithium layer back to the transition metal layer, thereby constructing unobstructed two-dimensional lithium-ion diffusion channels. This highly ordered structure helps reduce the kinetic energy barrier during lithium-ion insertion and extraction. Secondly, it helps reduce the lattice mismatch between the transition metal layer and the lithium layer, reducing anisotropic stress within the cathode active material during repeated charge and discharge, effectively suppressing lattice slip and intracrystalline crack formation, and reducing side reactions caused by continuous exposure of fresh surfaces to the electrolyte, thus improving the structural integrity and interface stability of single-crystal particles during cycling. In addition, the high cation order can also reduce local crystal field disturbances caused by lithium-nickel antisite defects, stabilize the redox potential of the cathode active material, contribute to a stable voltage plateau, and improve battery life.

[0048] The cation order degree μ was calculated using X-ray diffraction and Rietveld refinement. Specific testing methods included: performing X-ray diffraction tests on the single-crystal cathode active material at 2θ1 intervals of 10°–80° to obtain the full XRD spectrum; performing Rietveld refinement fitting on the full XRD spectrum; comparing it with a standard card; removing background functions; and restoring the Ni occupancy rate at the 3a site in the long-range ordered structure, which is the Ni-occupied Li occupancy rate.

[0049] In some embodiments, the equivalent number of lamellar layers N of the positive electrode active material (003) crystal plane is... (003) The effective number of lamellar layers N of the positive electrode active material (104) crystal plane is 160~240. (104) The range is 250-400; among which, D(003) The average thickness of the positive electrode active material in the unit cell perpendicular to the (003) crystal plane is expressed in nm. (003) The interplanar spacing of the (003) crystal plane in the unit cell of the positive electrode active material is expressed in nm. D (104) The average thickness of the positive electrode active material in the unit cell perpendicular to the (104) crystal plane is expressed in nm and d. (104) The interplanar spacing of the (104) crystal plane in the unit cell of the positive electrode active material is expressed in nm.

[0050] As an example, the equivalent number of lamellar layers N of the (003) crystal plane of the positive electrode active material (003) It can be 160, 170, 180, 190, 200, 210, 220, 230 or 240, etc.; (104) the equivalent number of lamellar layers N of the crystal plane. (104) It can be 250, 270, 290, 310, 330, 350, 370, 390 or 400, etc.

[0051] When the equivalent number of lamellar layers of the (003) crystal plane and the (104) crystal plane of the positive electrode active material are within the above range, the Li-C100 is further improved. + Diffusion kinetics reduces the solid-phase migration path during lithium-ion insertion and extraction within the layer, improving the rate performance of the material. An appropriate number of crystal lamellae ensures the particle size of the material; an excessively large number of lamellae increases the difficulty of atomic orderly stacking and reduces the intracrystalline order. Furthermore, an appropriate number of equivalent lamellae stabilizes the expansion and contraction of the c-axis of the cathode active material lattice during charge and discharge, mitigating structural distortion and collapse, suppressing heterogeneous reactions inside and outside the single crystal due to excessively large single crystal size, and improving the cycle stability of the cathode active material. This application controls the N0 of the cathode active material. (003) and N (104) Within the aforementioned range, the cycle performance and safety performance of the battery can be further improved.

[0052] As an example, N (003) N (104) The specific testing method is as follows: The XRD test results of the positive electrode active material are calculated using the Scherrer formula and the Bragg formula, which respectively yields the average thickness D of the positive electrode active material unit cell perpendicular to a certain crystal plane. (hkl) And the interplanar spacing d of a certain crystal plane in the unit cell of the positive electrode active material (hkl) ,by Calculate the equivalent number of lamellar layers along a specific crystal plane in the unit cell of the positive electrode active material.

[0053] As an example, , , where K is the Scherrer constant 0.89, λ is the test X-ray wavelength, β1 is the half width at half maximum (FWHM) of the diffraction peak of the (003) crystal plane in the unit cell of the positive electrode active material, and θ1 is the Bragg diffraction angle of the (003) crystal plane in the unit cell of the positive electrode active material. .

[0054] As an example, , , where K is the Scherrer constant 0.89, λ is the test X-ray wavelength, β2 is the half-width at half maximum (FWHM) of the diffraction peak of the (104) crystal plane in the cell of the positive electrode active material, and θ2 is the Bragg diffraction angle of the (104) crystal plane in the cell of the positive electrode active material. .

[0055] XRD testing conditions: The XRD pattern was obtained using a Rigaku powder X-ray diffractometer (Smart Lab 9kW) after fine-tuning. The Cu target wavelength was 1.5418462 Å, tube voltage was 40 kV, tube current was 200 mA, scanning speed was 5 Hz / min, and the scanning range was 10–90 Å. A one-dimensional detector (1D) was used. Specific testing conditions were: operating temperature: 21 ± 5 °C, humidity: <65%; cooling water circulator: temperature: 23 ± 1 °C, water pressure: 0.36 MPa; high-pressure refrigerant: 0.8 MPa–1.8 MPa, low-pressure refrigerant: 0.4 MPa–0.7 MPa; step size: 0.0200 °C.

[0056] In some embodiments, the positive electrode active material satisfies the chemical formula: Li 1+a Ni u Co v Mn w M m J n O 2+b Wherein, -0.05≤a≤0.3, 0.8≤u≤1, 0≤v≤0.2, 0≤w≤0.2, 0<m≤0.02, 0≤n≤4, -0.05≤b≤0.3; element M includes at least one of Zr, Al, Ce, Ba, Mg, and Sr; element J includes at least one of Al, Zr, F, B, Cl, Br, I, S, W, La, and P. Therefore, by introducing dopant element M, the lattice parameters and long-range order of the cathode active material can be controlled, coordinating the balance between high density and fast ion diffusion channels, forming fast lithium-ion transport channels within the dense lattice, and significantly improving the rate performance of the cathode active material. Furthermore, by doping with element M, slightly different heterostructures can be constructed on the surface and near the surface of the cathode active material compared to the interior, suppressing lattice distortion and irreversible phase transitions during deep delithiation, alleviating differences in electrochemical reactions inside and outside the single crystal, reducing local stress and delamination risk, and improving electrochemical stability.

[0057] For example, 'a' can be -0.05, -0.04, -0.03, -0.02, -0.01, 0, 0.01, 0.05, 0.08, 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, or 0.3, etc.; 'u' can be 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, or 1, etc.; 'v' can be 0, 0.05, 0.1, 0.12, 0.14, etc. The values ​​for 0.16, 0.18, or 0.2 are as follows: w can be 0, 0.05, 0.1, 0.12, 0.14, 0.16, 0.18, or 0.2; m can be 0.001, 0.005, 0.01, 0.012, 0.014, 0.016, 0.018, or 0.02; n can be 0, 1, 2, 3, or 4; b can be -0.05, -0.03, -0.01, 0, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, or 0.3.

[0058] In some embodiments, the ratio of the molar amount of element M to the sum of the molar amounts of nickel, cobalt, and manganese, n(M) / n(Ni+Co+Mn), is greater than 0.005, for example, it can be 0.006, 0.007, 0.008, 0.009, 0.010, 0.012, 0.015, or 0.02. Therefore, the doping amount of element M is moderate, which can utilize the dopant ions to stabilize the crystal lattice and suppress cracks, while having a relatively small impact on the specific capacity and lithium-ion diffusion rate.

[0059] In some embodiments, the cross-sectional SEM image of the positive electrode active material, such as Figure 2 As shown, the molar amount of element M on the surface of the positive electrode active material is greater than the molar amount of element M inside the positive electrode active material. Therefore, by performing shallow surface doping on the positive electrode active material, a heterostructure with slight differences between the single-crystal surface and interior is constructed. Introducing more crystal orientations different from the interior onto the surface can effectively suppress interfacial side reactions, reduce electrolyte erosion and transition metal dissolution, and alleviate lattice strain and local stress concentration during cycling, while maintaining the stability of the main particle structure. This reduces the risk of surface-to-internal phase transition differences and delamination, and inhibits further erosion of the surface CEI into the interior, thereby significantly improving the cycle life of the positive electrode active material.

[0060] Specifically, the cross-sectional SEM image of the positive electrode active material was obtained by using a Hitachi S-4800 scanning electron microscope from Japan, with a magnification of 3K.

[0061] In a second aspect, this application proposes a method for preparing the aforementioned positive electrode active material. This method effectively suppresses lattice defect formation and constructs a locally ordered superlattice structure by precisely controlling the amount of lithium source added during the first and second sintering processes. Simultaneously, it enhances structural stability by constructing a heterostructure on the surface of the positive electrode active material through M doping. Furthermore, the preparation method is simple, easy to operate, and readily applicable to industrial production. Specifically, the method includes: S1: A co-precipitation reaction is carried out after mixing nickel source, cobalt source, manganese source, precipitant and complexing agent to obtain the precursor.

[0062] In some embodiments, the nickel source includes at least one of the following: a nickel sulfate, a nickel nitrate, a nickel chloride, and a nickel oxalate; and / or, the cobalt source includes at least one of the following: a cobalt sulfate, a cobalt nitrate, a cobalt chloride, and a cobalt oxalate; and / or, the manganese source includes at least one of the following: a manganese sulfate, a cobalt nitrate, a manganese chloride, and a manganese oxalate. Therefore, the raw materials are widely available, the cost is low, and large-scale promotion is easy.

[0063] In some embodiments, the median particle size of the precursor is 2 μm to 5 μm, for example, it can be 2 μm, 3 μm, 4 μm, or 5 μm. This helps to obtain a positive electrode active material with a suitable particle size, achieving the closest possible packing between particles while maintaining high structural stability.

[0064] As an example, a nickel source, cobalt source, manganese source, precipitant, and complexing agent can be mixed, and the pH of the mixed solution can be adjusted to 9-12 to allow for sufficient co-precipitation and crystal nucleation. When the crystal nuclei grow to a median particle size of approximately 1 μm-1.2 μm, the pH of the mixed aqueous solution can be adjusted to 9-13, where the pH2 value is greater than the pH1 value by a difference of 0.1-1, controlling the crystal growth to a median particle size of 2 μm-5 μm. After the reaction is complete, the mixture is aged to obtain the precursor.

[0065] S2: The precursor, the first lithium source and the first M source are mixed and then subjected to a first sintering process to obtain a first sintered material.

[0066] In some embodiments, the first lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate; and / or, the first M source includes at least one of the oxide, chloride, carbonate, and sulfate corresponding to element M. Therefore, the raw materials are widely available, the cost is low, and large-scale promotion is easy.

[0067] In some embodiments, the ratio of the molar amount of lithium corresponding to the first lithium source to the total molar amount of nickel, cobalt and manganese in the precursor is 0.8 to 0.95, for example, it can be 0.8, 0.82, 0.84, 0.86, 0.88, 0.91, 0.93 or 0.95.

[0068] In the lithiation process of single-crystal cathodes, a small amount of primary lithium source is first added. By precisely controlling the lithium stoichiometry, the ratio of the molar amount of lithium to the total molar amount of nickel, cobalt, and manganese in the precursor meets the aforementioned range. This effectively suppresses the formation of lattice defects and constructs a locally ordered superlattice structure. The locally ordered superlattice, by regulating the ordered substitution of transition metal ions in the lithium layer and the transition metal layer, forms a superexchange interaction network, significantly reducing the lithium-ion migration barrier between adjacent octahedral sites. Simultaneously, it enhances the stability of the lattice oxygen framework, suppresses over-ripening during micron-scale single-crystal growth, and not only improves the lithium-ion transport rate but also effectively inhibits the structural degradation of single-crystal materials during cycling.

[0069] In some embodiments, the temperature of the first sintering treatment is 700℃~900℃ (e.g., 700℃, 750℃, 800℃, 850℃, or 900℃), and the time is 6h~12h (e.g., 6h, 7h, 8h, 9h, 10h, 11h, or 12h). This helps to reduce defects inside the positive electrode active material and form a complete crystal lattice structure.

[0070] In some embodiments, after the first sintering treatment, the sintered compound is cooled naturally to room temperature, and then crushed, sieved, and iron-removed to obtain the first sintered material.

[0071] S3: The first sintering material and the second lithium source are mixed and then subjected to a second sintering process to obtain a second sintering material, wherein the molar amount of lithium element corresponding to the second lithium source is greater than the molar amount of lithium element corresponding to the first lithium source.

[0072] In some embodiments, the second lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate. Therefore, the raw materials are widely available, the cost is low, and large-scale deployment is easily achieved.

[0073] In some embodiments, the ratio of the sum of the molar amounts of lithium corresponding to the first lithium source and the second lithium source to the total molar amounts of nickel, cobalt, and manganese in the precursor is 1.02 to 1.10, for example, it can be 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, or 1.10. Therefore, limiting the amount of the first lithium source helps suppress the formation of lattice defects in the positive electrode active material, constructing a locally ordered superlattice structure. Limiting the amount of the second lithium source provides precise lithium source replenishment for crystal growth, improving the integrity and uniformity of the crystal structure.

[0074] In some embodiments, the temperature of the second sintering treatment is 700℃~850℃ (e.g., 700℃, 750℃, 800℃ or 850℃), and the time is 6h~12h (e.g., 6h, 7h, 8h, 9h, 10h, 11h or 12h). This helps to reduce defects inside the positive electrode active material and form a complete crystal lattice structure.

[0075] In some embodiments, after the second sintering treatment, the sintered compound is naturally cooled to room temperature, and then crushed, sieved, and iron-removed to obtain the second sintered material.

[0076] S4: The second sintering material and the second M source are mixed and then subjected to a third sintering process to obtain the positive electrode active material.

[0077] In this step, element M enters the surface layer of the positive electrode active material in the form of single atoms or clusters, realizing the construction of a surface heterostructure. This helps to suppress lattice distortion and irreversible phase transitions during deep delithiation, alleviate the differences in electrochemical reactions inside and outside the single crystal, reduce local stress and delamination risk, and improve electrochemical stability. It is understood that the second M source and the first M source can be the same or different, and those skilled in the art can choose flexibly according to the actual situation.

[0078] In some embodiments, the second M source includes at least one of the oxides, chlorides, carbonates, and sulfates corresponding to the M element. Therefore, the raw materials are widely available, the cost is low, and large-scale promotion is easy.

[0079] In some embodiments, the molar amount of element M corresponding to the second M source is greater than the molar amount of element M corresponding to the first M source. This facilitates the construction of an internal and external heterogeneous structure on the surface of the positive electrode active material.

[0080] In some embodiments, the temperature of the third sintering treatment is 500℃~700℃ (e.g., 500℃, 550℃, 600℃, 650℃, or 700℃), and the time is 3h~10h (e.g., 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h). Thus, element M can enter the surface structure of the single-crystal cathode active material in the form of single atoms or atomic clusters, realizing the construction of a surface heterostructure.

[0081] In some embodiments, after the third sintering treatment, the sintered compound is naturally cooled to room temperature, and then crushed, sieved, and iron removed to obtain the positive electrode active material.

[0082] In some embodiments, the method further includes: mixing the positive electrode active material and the J source and then performing a fourth sintering treatment; wherein the temperature of the fourth sintering treatment is 200℃~500℃ (e.g., 200℃, 300℃, 400℃, or 500℃), and the time is 3h~10h (e.g., 3h, 4h, 5h, 6h, 7h, 8h, 9h, or 10h). This facilitates the formation of a coating layer on the surface of the positive electrode active material, reduces the occurrence of side reactions between the positive electrode active material matrix and the electrolyte, and improves the cycle stability of the positive electrode active material.

[0083] In a third aspect of this application, a battery is provided, comprising a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer located on at least one side of the positive current collector, the positive active material layer comprising the positive active material described in the first aspect of this application or a positive active material prepared using the method described in the second aspect of this application. Therefore, the battery exhibits excellent rate performance and cycle stability.

[0084] The description of the various embodiments above tends to emphasize the differences between the various embodiments. The similarities or similarities between them can be referred to, and for the sake of brevity, they will not be repeated here.

[0085] The following specific embodiments illustrate the solution of this application. It should be noted that these embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0086] Example 1 (1) Nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in pure water at a molar ratio of 83:10:07 to obtain a mixed salt solution with a concentration of 2 mol / L. An 8 mol / L sodium hydroxide solution was prepared as a precipitant solution, and a 5.2 mol / L ammonia solution was prepared as a complexing agent solution. The sodium hydroxide and ammonia solutions were added to the reactor, and the pH was adjusted to 10.5. Nitrogen gas was introduced for protection, and the temperature of the reaction system was controlled at 60℃. The mixed salt solution, sodium hydroxide solution, and ammonia solution were added to the reactor through the inlet pipes, respectively. The stirring speed was maintained at 500 rpm, and the inlet flow rate of the mixed salt solution was controlled at 200 mL / h. The flow rates of the sodium hydroxide solution and ammonia solution were adjusted to keep the pH of the reaction system stable at 10.9 ± 0.05. The particle size D of the nuclei in the reaction system was determined. 50 After the particles grew to 1 μm, the pH of the solution was adjusted to 11.0 ± 0.05, the flow rate of the mixed salt solution was adjusted to 500 mL / h, the stirring speed was increased to 700 rpm, and the reaction temperature was kept constant. The reaction proceeded until the average particle size D in the solution reached 1 μm. 50After growing to 3μm, the precursor was aged for 1 hour, then separated, washed, and dried. (2) The above precursor, lithium hydroxide and cerium oxide are weighed separately in an elemental molar ratio of 1:0.90:0.005, mixed evenly in a mixer, and subjected to a first sintering treatment in an oxygen furnace. The temperature of the first sintering treatment is 830℃ and the time is 8h. The oxygen concentration in the oxygen furnace is greater than 95 vol.%. After naturally cooling to room temperature, the material is crushed and sieved to obtain the first sintered material.

[0087] (3) Weigh the first sintering material and lithium hydroxide separately at an elemental molar ratio of 1:0.15, mix them evenly in a mixer, and then perform a second sintering treatment in an oxygen furnace. The temperature of the second sintering treatment is 800℃, the time is 8h, and the oxygen concentration in the oxygen furnace is greater than 95 vol.%, so as to obtain the second sintering material. The ratio of the sum of the molar amounts of lithium elements corresponding to the first lithium source and the second lithium source to the total molar amounts of nickel, cobalt, and manganese elements in the precursor is 1.05.

[0088] (4) The above-mentioned second sintering material and alumina were mixed evenly in a high-speed mixer at a molar ratio of 1:0.005. A third sintering treatment was then performed in an oxygen furnace at a temperature of 650℃ for 6 hours, with an oxygen concentration greater than 90 vol.%. After cooling, sieving, and iron removal, the third sintering material, i.e., the positive electrode active material, was obtained. The SEM image is shown below. Figure 1 .

[0089] Example 17 The difference from Example 1 is that the above-mentioned third sintering material and boric acid were mixed evenly in a high-speed mixer at a molar ratio of 1:0.004, and then subjected to a fourth sintering treatment in an oxygen furnace at a temperature of 350°C for 6 hours with an oxygen concentration greater than 90 vol.%. After cooling, sieving, and iron removal, the positive electrode active material was obtained.

[0090] The differences between other embodiments and comparative examples and embodiment 1 are shown in Tables 1-1, 1-2 and 1-3.

[0091] Table 1-1

[0092] Table 1-2

[0093] Table 1-3

[0094] The positive electrode active material prepared above was subjected to the aforementioned tests, and the test results are shown in Table 2.

[0095] Table 2

[0096] The positive electrode active materials obtained in the above embodiments and comparative examples are assembled into batteries using the following method: (1) Electrode preparation: The positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF) were thoroughly mixed with an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 95:3:2 to form a uniform slurry. The slurry was coated onto aluminum foil and dried at 120°C for 12 hours. Then, it was pressed into shape using a pressure of 100 MPa to produce a positive electrode sheet with a diameter of 12 mm and a thickness of 120 μm. The loading of the positive electrode active material was 15 mg / cm³. 2 .

[0097] (2) Battery assembly: In an argon-filled glove box with both water and oxygen content less than 5 ppm, the positive electrode, separator, negative electrode, and electrolyte were assembled into a 2025 coin cell and left to stand for 6 hours. The negative electrode used a lithium metal sheet with a diameter of 17 mm and a thickness of 1 mm; the separator used a polyethylene porous membrane (Celgard 2325) with a thickness of 25 μm; and the electrolyte used was a mixture of equal amounts of 1 mol / L LiPF6, ethylene carbonate (EC), and diethyl carbonate (DEC).

[0098] The electrochemical performance of the batteries assembled in the aforementioned examples and comparative examples was tested using the Shenzhen Xinwei Battery Testing System. The charge-discharge current density at 0.1C was 200 mA / g. The test results are shown in Table 3.

[0099] (1) Cyclic performance test: The charge and discharge voltage range was controlled at 3.0V~4.3V. At a constant temperature of 45℃, the coin cell was charged and discharged twice at 0.1C to obtain the first charge specific capacity C2 of the battery. Then, it was charged and discharged 80 times at 1C, and the discharge specific capacity C of the 80th charge was taken. 80 To evaluate the high-temperature capacity retention of the positive electrode active material, the high-temperature capacity retention rate = C 80 / C2×100%.

[0100] (2) Rate performance test: The charge and discharge voltage range was controlled at 3.0V~4.3V. At room temperature, the coin cell was charged and discharged twice at 0.1C, and then charged and discharged once at 0.2C, 0.33C, 0.5C, 1C and 2C respectively. The rate performance of the positive electrode active material was evaluated by the ratio of the initial discharge specific capacity at 2C to the discharge specific capacity at 0.1C. Among them, the initial discharge specific capacity at 0.1C is the discharge specific capacity of the coin cell in the first cycle, and the discharge specific capacity at 2C is the discharge specific capacity of the coin cell in the seventh cycle.

[0101] (3) Diffusion coefficient test: EIS testing and analysis were performed. The cell was charged to 4.3V at a constant current of 0.1C, charged at a constant voltage for 30 minutes, and then discharged to 3.0V at a constant current of 0.1C. Subsequently, it was charged to 4.3V at a constant current of 0.1C. The fully charged half-cell was removed, and EIS testing was performed in the frequency range of 100kHz to 0.01Hz with an amplitude of 10mV. Z can be obtained according to the following formula. re With ω -1 / 2 The slope σ of the fitted line: Z re = R s + R ct + σω -1 / 2 ; ω = 2πf; Among them, Z re R is the real part of the impedance spectrum obtained from the test. s R is the resistance of the solution. ct ω is the charge transfer resistor, f is the angular frequency, f is the test frequency, and σ is the Warburg factor.

[0102] Then, based on the formula for calculating the lithium-ion diffusion coefficient, the bulk Li of the material is obtained. + Diffusion coefficient D Li+ : D Li+ =R 2 T 2 / (2A 2 n 4 F 4 C 2 σ 2 ); Where R is the ideal gas constant, T is the absolute temperature, A is the cross-sectional area of ​​the electrode, n is the number of electrons transferred, F is the Faraday constant, and C is the lithium ion concentration in the electrode.

[0103] (4) Thermal decomposition initiation temperature at 100% SOC: The battery containing the positive electrode active material was charged and discharged at 0.1C for two weeks, and then charged to 4.3V in the third week. The battery was disassembled in a glove box, the electrode was cleaned with DMC for 30 min, and cut into three electrode sheets with a diameter of 4 mm. The sheets were placed in a high-voltage crucible, and electrolyte was added (electrolyte / active material = 0.4 μL / mg). The high-voltage crucible was sealed and tested. The test conditions were 30℃~350℃, nitrogen, 5° / min. The exothermic peak of the positive electrode active material in the electrode sheet was obtained, and the initiation temperature was read.

[0104] Table 3

[0105] This application achieves structural stability by precisely controlling the amount of lithium source added during the first and second sintering processes. The lithium deficiency during the first sintering process ensures the continuity of the long-range NiCoMn framework, and the lithium supplementation during the second sintering process ensures complete lattice filling and effectively suppresses the formation of lattice defects. At the same time, the near-surface disorder is created by shallow doping with M elements, thereby improving structural stability.

[0106] As can be seen from the table above, the long-range order of the positive electrode active material prepared in the embodiments of this application is within the scope defined by this application. It has good internal crystallinity, consistent arrangement direction, low cation disorder, and good capacity utilization, rate performance and cycle stability.

[0107] In Comparative Example 1, the first sintering treatment time was too long, resulting in an excessively high long-range order of the positive electrode active material. This made it unable to buffer anisotropic volume changes during high-pressure cycling, leading to concentrated initiation of microcracks and aggravated interfacial side reactions, thereby reducing cycling stability.

[0108] The temperature of the first sintering treatment in Comparative Example 2 was too high, resulting in severe lithium-nickel mixing and increased disorder, which led to poor capacity utilization, cycle performance and thermal stability of the battery.

[0109] In Comparative Example 3, excessive Li was directly added during the first sintering process, which caused Li to occupy Ni sites, resulting in increased mixing and disorder, leading to poor capacity utilization, cycle performance, and thermal stability of the battery.

[0110] In Comparative Example 4, no second M source was added during the third sintering process, which prevented shallow doping on the surface of the positive electrode active material. This resulted in excessively high long-range order of the positive electrode active material, leading to poor capacity utilization and rate performance of the battery.

[0111] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material includes single crystal particles, the positive electrode active material includes nickel-cobalt-manganese ternary materials, and the long-range order η of the positive electrode active material is 0.85~0.96; in, ; D S The average size of the single crystal particle; D x The average subgrain size of a single long-range ordered crystal is calculated from the refined X-ray diffraction pattern of the positive electrode active material.

2. The positive electrode active material according to claim 1, characterized in that, The long-range order η of the positive electrode active material is 0.88~0.

93.

3. The positive electrode active material according to claim 1, characterized in that, 0.8μm≤D s ≤1.8μm; 0.7μm≤D x ≤1.7μm。 4. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material has a cation order degree μ of 95%~99%; optionally, 95.5%~98.5%. in, ; n(Nio) is the number of Ni atoms mixed in the Li sites in the positive electrode active material, and n(Nim) is the total number of Ni atoms in the lattice of the positive electrode active material.

5. The positive electrode active material according to claim 1, characterized in that, The equivalent number of lamellar layers N of the positive electrode active material (003) crystal plane (003) The effective number of lamellar layers N of the positive electrode active material (104) crystal plane is 160~240. (104) The range is 250-400; among which, D (003) The average thickness of the positive electrode active material in the unit cell perpendicular to the (003) crystal plane is expressed in nm. (003) The interplanar spacing of the (003) crystal plane in the unit cell of the positive electrode active material is expressed in nm. D (104) The average thickness of the positive electrode active material in the unit cell perpendicular to the (104) crystal plane is expressed in nm and d. (104) The interplanar spacing of the (104) crystal plane in the unit cell of the positive electrode active material is expressed in nm.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that, Satisfies the chemical formula: Li 1+a Ni u Co v Mr w M m J n O 2+b ; Wherein, -0.05≤a≤0.3, 0.8≤u≤1, 0≤v≤0.2, 0≤w≤0.2, 0<m≤0.02, 0≤n≤4, -0.05≤b≤0.3; element M includes at least one of Zr, Al, Ce, Ba, Mg, and Sr; element J includes at least one of Al, Zr, F, B, Cl, Br, I, S, W, La, and P.

7. The positive electrode active material according to claim 6, characterized in that, In the positive electrode active material, the ratio of the molar amount of element M to the sum of the molar amounts of elements nickel, cobalt, and manganese, n(M) / n(Ni+Co+Mn), is greater than 0.

005.

8. The positive electrode active material according to claim 6, characterized in that, The molar amount of M element on the surface of the positive electrode active material is greater than the molar amount of M element inside the positive electrode active material.

9. A method for preparing the positive electrode active material according to any one of claims 1 to 8, characterized in that, include: A precursor is obtained by co-precipitation reaction of a nickel source, a cobalt source, a manganese source, a precipitant, and a complexing agent. The precursor, the first lithium source, and the first M source are mixed and subjected to a first sintering treatment to obtain a first sintered material, wherein the ratio of the molar amount of lithium element corresponding to the first lithium source to the total molar amount of nickel element, cobalt element, and manganese element in the precursor is 0.8 to 0.

95. The first sintering material and the second lithium source are mixed and then subjected to a second sintering process to obtain the second sintering material. The second sintering material and the second M source are mixed and then subjected to a third sintering process to obtain the positive electrode active material.

10. The method according to claim 9, characterized in that, The ratio of the sum of the molar amounts of lithium corresponding to the first lithium source and the second lithium source to the total molar amounts of nickel, cobalt and manganese in the precursor is 1.02 to 1.

10.

11. The method according to claim 9 or 10, characterized in that, The first sintering treatment is performed at a temperature of 700℃~900℃ for a time of 6h~12h; and / or, The second sintering treatment is performed at a temperature of 700℃~850℃ for 6h~12h.

12. The method according to claim 9 or 10, characterized in that, The molar amount of M element corresponding to the second M source is greater than the molar amount of M element corresponding to the first M source.

13. The method according to claim 9 or 10, characterized in that, The third sintering treatment is performed at a temperature of 500℃ to 700℃ for a time of 3 hours to 10 hours.

14. The method according to claim 9, characterized in that, Also includes: The positive electrode active material and the J source are mixed and then subjected to a fourth sintering treatment; wherein the temperature of the fourth sintering treatment is 200℃~500℃ and the time is 3h~10h.

15. A battery, characterized in that, The invention includes a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material layer located on at least one side of the positive current collector, the positive active material layer comprising the positive active material according to any one of claims 1 to 8 or the positive active material prepared by the method according to any one of claims 9 to 14.

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