Positive electrode material precursor, single-crystal positive electrode material, preparation method of single-crystal positive electrode material and lithium ion battery

Abstract

The chemical general formula of the single-crystal positive electrode material is LixNiaCobMncNdO2, x is larger than or equal to 0.98 and smaller than or equal to 1.1, a is larger than or equal to 0.50 and smaller than or equal to 0.98, b is larger than 0 and smaller than or equal to 0.20, c is larger than 0 and smaller than or equal to 0.30, d is larger than or equal to 0 and smaller than or equal to 0.10, a + b + c + d = 1, and N comprises at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; the standard deviation of the mass content of each element of Ni, Co and Mn in the single-crystal positive electrode material is less than or equal to 0.03; and the lattice strain epsilon is less than 0.2%. The crystal lattice strain of the single crystal positive electrode material is low, the diffusion energy barrier of lithium ions between microcrystals can be reduced, and the material shows relatively low DCR and good rate capability; and the generation of microcracks can be inhibited, and the cycle performance of the material is improved.

Description

Positive electrode material precursor, single crystal positive electrode material and preparation method, lithium ion battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the Patent Office of China on October 13, 2023, with application number "202311331910.3" and application name "Positive electrode material precursor, single crystal positive electrode material and preparation method, lithium-ion battery", all of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the technical field of cathode materials, and in particular to cathode material precursors, single crystal cathode materials and preparation methods, and lithium-ion batteries. Background Art

[0004] Lithium-ion cathode materials are primarily divided into lithium iron phosphate (LFP) and ternary materials. LFP, due to its superior cost, cycle life, and thermal stability, is suitable for commercial vehicles, mid- and low-end passenger vehicles, and energy storage applications. Ternary materials offer high energy density and excellent low-temperature performance, making them suitable for mid- to high-end passenger vehicles.

[0005] Traditional polycrystalline ternary cathode materials consist of tightly packed primary particles (several hundred nanometers) clustered into spherical secondary particles (typically >10 μm in diameter). During charge and discharge, as the crystal lattice contracts, localized stresses easily develop along grain boundaries, causing structural collapse and microcracks, leading to rapid capacity decay. Single-crystalization is one approach to improving the cycling performance of ternary materials. Single-crystal ternary materials consist of dispersed primary particles (typically a few micrometers in diameter, with the vast majority of particles being single grains with uniform orientation) devoid of secondary spherical particles. The elimination of grain boundaries suppresses cracking in the cathode material during charge and discharge, resulting in excellent stability. However, single-crystal ternary materials also face other challenges. The long Li diffusion path in single-crystal ternary materials results in slow Li transport, resulting in high direct current resistance (DCR) and poor rate performance. Furthermore, while single-crystal particles suppress cracking, interfacial slip and dislocation can still occur during cycling, further causing microcracks.

[0006] Ternary single-crystal cathode materials are generally prepared by high-temperature sintering a precursor compound containing Ni / Co / Mn and a lithium salt. During the sintering process, the formation of the cathode material is usually very slow, and the growth rate is uneven, resulting in stress concentration within the formed cathode material. In addition, due to the limitations of ion diffusion, the distribution of elements in the ternary material has concentration differences, resulting in a mismatch in the material's internal lattice parameters. This, on the one hand, hinders the transmission of lithium ions, thereby increasing the impedance of the cathode material and reducing its rate performance. On the other hand, internal lattice microstress causes the cathode material to crack and pulverize during cycling, reducing its cyclic performance.

[0007] Therefore, how to improve the rate performance of single crystal positive electrode materials, reduce impedance, and further improve cycle performance are technical problems that still need to be solved.

[0008] Summary of the Invention

[0009] The purpose of the present application is to provide a positive electrode material precursor, a single crystal positive electrode material and a preparation method, and a lithium-ion battery. The single crystal positive electrode material provided in the present application has low lattice strain, which can reduce the diffusion energy barrier of lithium ions between microcrystals and increase the Li ion diffusion coefficient, so that the single crystal positive electrode material exhibits a lower DCR and good rate performance of the single crystal positive electrode material; it can also reduce the occurrence of crystal plane slip, dislocation and other phenomena, thereby inhibiting the generation of microcracks, improving the structural stability of the single crystal positive electrode material, and thus improving the cycle performance of the single crystal positive electrode material.

[0010] In the first aspect, the present invention provides a single crystal cathode material, the chemical formula of which is Li x Ni a Co b Mn c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn, and Y;

[0011] When observing the single crystal positive electrode material with a scanning electron microscope, at a magnification of 3K, 10 points of the single crystal positive electrode material are randomly selected for EDS point scanning to test the Ni, Co, and Mn contents. In the EDS spectrum results of the single crystal positive electrode material, the standard deviation of the mass content of each element Ni, Co, and Mn in the single crystal positive electrode material is ≤0.03;

[0012] The lattice strain of the single crystal positive electrode material is ε, and ε is less than 0.2%.

[0013] In some embodiments, the single crystal cathode material includes SO4 2- , SO4 2- The content of is δ, where 0ppm≤δ≤800ppm.

[0014] In some embodiments, the single crystal positive electrode material contains at least one single grain with the same orientation, wherein the average grain size of the single grain is 1 μm to 5 μm.

[0015] In some embodiments, the grain size of the single crystal positive electrode material is D, 150 nm < D < 250 nm.

[0016] In some embodiments, the average particle size D of the single crystal positive electrode material is 50 1.5μm~5μm.

[0017] In some embodiments, the tap density of the single crystal cathode material is greater than 1.5 g / cm 3 .

[0018] In some embodiments, the range of the mass content of each element of Ni, Co and Mn in the single crystal positive electrode material is ≤0.08.

[0019] In the second aspect, the present invention provides a positive electrode material precursor, the chemical formula of which is Ni a Co b Mn c N d O e , wherein, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, 1≤e≤1.15, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn, and Y;

[0020] The surface area weighted average particle size D[3,2] of the positive electrode material precursor is less than 2.0 μm, and the standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor is less than or equal to 0.05.

[0021] In some embodiments, the range of the mass content of each element Ni, Co and Mn in the positive electrode material precursor is ≤0.12.

[0022] In some embodiments, the cathode material precursor includes secondary particles, and the secondary particles include a plurality of agglomerated primary particles.

[0023] In some embodiments, the cathode material precursor includes secondary particles, the secondary particles include a plurality of agglomerated primary particles, and the primary particles are spherical.

[0024] In some embodiments, the cathode material precursor includes secondary particles, the secondary particles include a plurality of agglomerated primary particles, and the particle size of the primary particles is 20 nm to 1000 nm.

[0025] In some embodiments, the average particle size D of the positive electrode material precursor is 50 <3.5μm.

[0026] In some embodiments, the specific surface area of ​​the cathode material precursor is greater than 5m 2 / g.

[0027] In some embodiments, the tap density of the cathode material precursor is greater than 1 g / cm 3 .

[0028] In a third aspect, the present invention provides a method for preparing a single crystal positive electrode material, comprising the following steps:

[0029] A mixed solution containing nickel salt, cobalt salt and manganese salt is atomized and then thermally decomposed to obtain a positive electrode material precursor, wherein the surface area weighted average particle size D[3,2] of the positive electrode material precursor is less than 2.0 μm, and the standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor is ≤0.05; after the positive electrode material precursor is mixed with a lithium source, it is placed in an oxygen-containing atmosphere for sintering to obtain a single crystal positive electrode material, wherein the standard deviation of the mass content of each element Ni, Co and Mn in the single crystal positive electrode material is ≤0.03; the lattice strain of the single crystal positive electrode material is ε, and ε is less than 0.2%.

[0030] In some embodiments, the cathode material precursor includes SO4 2- , the SO4 2- The content is η, wherein 0ppm≤η≤1800ppm.

[0031] In some embodiments, the nickel salt includes at least one of nickel chloride, nickel sulfate, nickel nitrate, nickel carbonate, nickel oxalate, and nickel acetate.

[0032] In some embodiments, the cobalt salt includes at least one of cobalt chloride, cobalt oxalate, cobalt carbonate, cobalt sulfate, cobalt nitrate, and cobalt acetate.

[0033] In some embodiments, the manganese salt includes at least one of manganese chloride, manganese carbonate, manganese sulfate, manganese oxalate, manganese nitrate, and manganese acetate.

[0034] In some embodiments, the molar ratio of Ni, Co and Mn in the mixed solution is (50-98):(0-20):(0-30), and the content of Co and Mn in the mixed solution is not zero.

[0035] In some embodiments, the total metal concentration in the mixed solution is 200 g / L to 500 g / L.

[0036] In some embodiments, the mixed solution further includes a dopant containing N element, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y.

[0037] In some embodiments, the chemical formula of the positive electrode material precursor is Ni a Co b Mn c N d O e , wherein, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, 1≤e≤1.15, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y.

[0038] In some embodiments, the range of the mass content of each element Ni, Co and Mn in the positive electrode material precursor is ≤0.12.

[0039] In some embodiments, the flow rate of the mixed solution is 100 L / h to 900 L / h.

[0040] In some embodiments, the pressure of the atomization treatment is 0.4 MPa to 0.8 MPa.

[0041] In some embodiments, the primary sintering temperature is 500°C to 850°C.

[0042] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium sulfate, lithium chloride, lithium nitrate, and lithium oxalate.

[0043] In some embodiments, the molar ratio of lithium in the lithium source to the sum of nickel, cobalt, and manganese in the positive electrode material precursor is 0.98 to 1.10.

[0044] In some embodiments, the sintering temperature is 750°C to 950°C.

[0045] In some embodiments, the sintering time is 10 hours to 30 hours.

[0046] In a fourth aspect, an embodiment of the present application provides a lithium-ion battery, which includes the single crystal positive electrode material described in the first aspect or the single crystal positive electrode material prepared by the preparation method of the single crystal positive electrode material described in the third aspect.

[0047] Compared with the prior art, the technical solution of this application has at least the following beneficial effects:

[0048] The single crystal positive electrode material provided in the present application is randomly selected from 10 points of the single crystal positive electrode material for EDS point scanning to test the Ni, Co, and Mn content. In the EDS spectrum results of the single crystal positive electrode material, the standard deviation of the mass content of each element Ni, Co, and Mn in the single crystal positive electrode material is ≤0.03, indicating that the distribution uniformity of Ni, Co, and Mn elements inside the single crystal positive electrode material is good, which is conducive to reducing the crystal structure defects of the single crystal positive electrode material; the lattice strain ε of the single crystal positive electrode material is less than 0.2%, which can reduce the diffusion energy barrier of lithium ions between microcrystals and increase the Li ion diffusion coefficient, so that the single crystal positive electrode material exhibits good rate performance and low DCR; at the same time, low lattice strain can also inhibit the generation of microcracks in the single crystal positive electrode material, thereby improving the cycle performance of the single crystal positive electrode material.

[0049] The positive electrode material precursor provided in the present application has a surface area weighted average particle size D[3,2]<2.0μm, high reaction activity, and is beneficial to improving the reaction efficiency and mass transfer efficiency in the subsequent preparation process of the positive electrode material from the positive electrode material precursor; at the same time, the standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor obtained by the above preparation method is ≤0.05, indicating that the distribution uniformity of Ni, Co and Mn elements in the positive electrode material precursor is good; using the positive electrode material precursor to prepare the positive electrode material can improve the distribution uniformity of Ni, Co and Mn elements in the positive electrode material, so that the positive electrode material prepared by the positive electrode material precursor has fewer crystal structure defects and smaller lattice stress.

[0050] The present application provides a method for preparing a single crystal positive electrode material, wherein a mixed solution containing nickel salt, cobalt salt and manganese salt is subjected to atomization treatment and then thermally decomposed to obtain a positive electrode material precursor. The surface area weighted average particle size D[3,2] of the positive electrode material precursor is less than 2.0 μm, and the reaction activity is high, which is beneficial to improving the reaction efficiency and mass transfer efficiency of the positive electrode material precursor and the lithium source during the subsequent high-temperature sintering process; at the same time, the standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor obtained by the above preparation method is ≤0.05, indicating that the distribution uniformity of Ni, Co and Mn in the positive electrode material precursor is good; furthermore, the single crystal positive electrode material prepared by the above positive electrode material precursor after subsequent sintering with the lithium source has a weighted average particle size D[3,2] less than 2.0 μm, and the reaction activity is high, which is beneficial to improving the reaction efficiency and mass transfer efficiency of the positive electrode material precursor and the lithium source during the subsequent high-temperature sintering process; at the same time, the standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor obtained by the above preparation method is ≤0.05, indicating that the distribution uniformity of Ni, Co and Mn in the positive electrode material precursor is good; furthermore, the weighted average particle size D[3,2] of the positive electrode material precursor is less than 2.0 μm, and the reaction activity is high, which is beneficial to improving the reaction efficiency and mass transfer efficiency of the positive electrode material precursor and the lithium source during the subsequent high-temperature sintering process ... The standard deviation of the mass content of these elements is ≤0.03, and the distribution uniformity of Ni, Co, and Mn elements inside the single crystal positive electrode material is good, which is conducive to reducing the crystal structure defects of the single crystal positive electrode material; and the lattice strain of the single crystal positive electrode material is low, and its lattice strain ε is less than 0.2%, which can reduce the diffusion energy barrier of lithium ions between microcrystals and improve the Li ion diffusion coefficient, so that the single crystal positive electrode material exhibits good rate performance and low DCR; at the same time, low lattice strain can also inhibit the generation of microcracks in the single crystal positive electrode material, thereby improving the cycle performance of the single crystal positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The present application is further described below with reference to the accompanying drawings and examples.

[0052] FIG1 is a SEM morphology of the cathode material precursor prepared in Example 1 of the present application;

[0053] FIG2 is another SEM morphology of the cathode material precursor prepared in Example 1 of the present application;

[0054] FIG3 is an EDS spectrum result of the cathode material precursor prepared in Example 1 of the present application;

[0055] FIG4 is a Williamsone-Hall analysis fitting curve of the single crystal positive electrode material prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0056] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0057] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0058] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0059] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0060] In the first aspect, the present invention provides a single crystal cathode material, the chemical formula of which is Li x Ni a Co b Mn c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn, and Y;

[0061] When observing the single crystal positive electrode material with a scanning electron microscope, at a magnification of 3K, 10 points of the single crystal positive electrode material are randomly selected for EDS point scanning to test the Ni, Co, and Mn contents. In the EDS spectrum results of the single crystal positive electrode material, the standard deviation of the mass content of each element Ni, Co, and Mn in the single crystal positive electrode material is ≤0.03;

[0062] The lattice strain of the single crystal positive electrode material is ε, and ε is less than 0.2%.

[0063] The single crystal positive electrode material provided in the present application is randomly selected from 10 points of the single crystal positive electrode material for EDS point scanning to test the Ni, Co, and Mn content. In the EDS spectrum results of the single crystal positive electrode material, the standard deviation of the mass content of each element Ni, Co, and Mn in the single crystal positive electrode material is ≤0.03, indicating that the distribution uniformity of Ni, Co, and Mn elements inside the single crystal positive electrode material is good, which is conducive to reducing the crystal structure defects of the single crystal positive electrode material; the lattice strain ε of the single crystal positive electrode material is less than 0.2%, which can reduce the diffusion energy barrier of lithium ions between microcrystals and increase the Li ion diffusion coefficient, so that the single crystal positive electrode material exhibits good rate performance and low DCR; at the same time, low lattice strain can also inhibit the generation of microcracks in the single crystal positive electrode material, thereby improving the cycle performance of the single crystal positive electrode material.

[0064] Specifically, the value of x can be 0.98, 0.99, 1.0, 1.01, 1.03, 1.05, 1.08, 1.09 or 1.1, etc., and is not limited here.

[0065] The specific value of a can be 0.50, 0.55, 0.60, 0.63, 0.70, 0.75, 0.80, 0.85, 0.88, 0.90, 0.95 or 0.98; the value of b can be 0.01, 0.05, 0.08, 0.10, 0.11, 0.13, 0.15, 0.18 or 0.20; the value of c can be 0.01, 0.05, 0.10, 0.15, 0.18, 0.20, 0.23, 0.27 or 0.30; the value of d can be 0, 0.01, 0.03, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.10, etc., which are not limited here.

[0066] Specifically, the standard deviation of the mass content of each element Ni, Co and Mn in the single crystal positive electrode material can be 0.01, 0.015, 0.02, 0.025, 0.026, 0.028 or 0.03, etc., which is not limited here.

[0067] In some embodiments, the range of the mass content of each element Ni, Co and Mn in the single crystal positive electrode material is ≤0.08, and can be specifically 0.01, 0.02, 0.028, 0.03, 0.05, 0.057, 0.06, 0.07, 0.075 or 0.08, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0068] It can be understood that the lower the standard deviation and range of the mass content of each element Ni, Co and Mn in the single crystal positive electrode material, the higher the uniformity of the distribution of Ni, Co and Mn elements in the single crystal positive electrode material. The standard deviation and range of the mass content of each element Ni, Co and Mn in the single crystal positive electrode material of the present application are within the above ranges, indicating that the Ni, Co and Mn elements in the single crystal positive electrode material of the present application are uniformly distributed, which is beneficial to reducing lattice defects in the single crystal positive electrode material, reducing lattice stress, and improving the cycle performance and rate performance of the single crystal positive electrode material.

[0069] The lattice strain of the single crystal positive electrode material can specifically be 0.01%, 0.03%, 0.05%, 0.08%, 0.10%, 0.11%, 0.12%, 0.15%, 0.18% or 0.19%, etc., which is not limited here.

[0070] In some embodiments, the single crystal positive electrode material further includes a coating layer comprising a metal oxide or a lithium ion conductor, wherein the metal in the metal oxide comprises at least one of Al, Ti, Zr, Y, Nb, Mg, W, B, Ce, Co, and Mn. The coating layer can reduce direct contact between the single crystal positive electrode material and the electrolyte, reduce the occurrence of side reactions between the material and the electrolyte, and further improve the electrochemical performance of the single crystal positive electrode material.

[0071] In some embodiments, the free SO4 on the surface of the single crystal positive electrode material 2- The content of SO4 in single crystal positive electrode materials is less than or equal to 1000ppm, preferably ≤800ppm. 2- The content of can be 0ppm, 5ppm, 10ppm, 50ppm, 100ppm, 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm or 1000ppm. 2- When the content is within the above range, the positive electrode material has better rate and cycle performance. Because traditional ternary precursor materials use NiSO4, CoSO4, and MnSO4 as raw materials in the preparation process, the co-precipitated precursor will have a high content of residual sulfate ions. Sulfate ions are difficult to decompose, so the sulfate ion content on the surface of the corresponding positive electrode material formed by subsequent sintering is high (usually >1000ppm). Free sulfate ions will adversely affect the electrochemical properties of the positive electrode material. When the free SO4 2- When the content is high, SO4 2- Combined with Li ions, it binds some Li ions, causing the material capacity and rate to deteriorate; in addition, the free SO4 2- It will also affect the stability of the SEI film.

[0072] Free SO4 on the surface of single crystal cathode material 2- The content is related to the free SO4 on the surface of the cathode material precursor 2- The content has a strong inheritance, SO4 in the cathode material precursor 2- The higher the content, the free SO4 on the surface of the single crystal positive electrode material 2- The higher the content, the free SO4 2- The content is ≤1000ppm, which is more conducive to the preparation of surface free SO4 2- Positive electrode material with a content of ≤800ppm.

[0073] In order to reduce the SO4 2-In some embodiments, the Ni salt, Mn salt, Co salt and N salt each independently include at least one of chloride, nitrate, oxalate and acetate. Nitrate, chloride, oxalate and acetate of nickel, cobalt and manganese are easily decomposed at high temperature and no significant residue will remain, so they have little effect on the performance of the positive electrode material. By controlling the SO4 2- The content can even produce SO4 2- The content of SO4 is close to 0. However, this will require a higher purity of the raw materials, which will increase the cost of raw materials. 2- The Ni source, Co source, Mn source and N source in the ternary recycled material of impurities are used as metal sources, and the SO4 2- It is more economical to prepare the cathode material precursor with a certain content.

[0074] In some embodiments, in the metal salt mixed solution, based on the total mass of Ni, Co, and Mn, SO4 2- The content is ≤800ppm, which is more conducive to the preparation of surface free SO4 2- Single crystal positive electrode materials with lower content further improve the capacity and rate performance of single crystal positive electrode materials.

[0075] In some embodiments, the single crystal positive electrode material contains at least one single grain with the same orientation, wherein the average particle size of the single grain is 1 μm to 5 μm, such as 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc.

[0076] The single crystal particles of the positive electrode material of the present application contain at least one single grain with the same orientation, and the average particle size of the single particles that meet the above conditions is 1 to 5 μm when measured under EBSD testing. It can stably achieve its own high filling while preventing the occurrence of cracks due to reasons such as particles being squeezed after the particles reach their densest packing. The particles have the same orientation, which can alleviate the stress and strain of the positive electrode particles during the charge and discharge cycle process, greatly reducing the cracking of the particles during the cycle, thereby greatly improving the structural stability of the positive electrode particles.

[0077] It should be noted that the grain orientation of the positive electrode material can at least be tested by electron backscatter diffraction (EBSD), and 100 single grains with the same orientation are randomly selected to measure the particle size of each grain, and the arithmetic average is taken as the average particle size of the above single grains.

[0078] The difference between single crystal positive electrode materials and polycrystalline ternary positive electrode materials (i.e., polycrystalline secondary particles) is that the smallest particle of polycrystalline secondary particles is a secondary particle formed by the agglomeration of primary particles. For single crystal positive electrode materials, the smallest particle is usually a monomer primary particle in the micron range. Generally speaking, in addition to the EBSD testing method, the characterization methods such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) can also be used to determine whether the obtained positive electrode product is a single crystal material. For conventional single crystal positive electrode materials, SEM is also an important and reliable characterization method. The shape of single crystal particles generally appears as a regular or irregular polyhedron, and there is no significant particle agglomeration. TEM is an auxiliary second characterization method, which observes whether the crystal plane orientation of the obtained product is consistent, and is further characterized in combination with selected area electron diffraction (SAED). The above methods can all be used to determine whether it is a single crystal positive electrode material. For ease of understanding, the single crystal positive electrode material of the present application can be understood as a positive electrode material particle containing at least one single grain with the same orientation, and the average particle size of the above single grain is 1μm-5μm.

[0079] It can be understood that the single grain in the present application can be a single particle composed of a primary particle. The above-mentioned single crystal positive electrode material may also contain a small amount of "quasi-secondary particles" formed by the adhesion of several single particles. "Primary particle" refers to the smallest particle unit identified when observing the positive electrode active material through a scanning electron microscope, and "secondary particle" refers to a secondary structure formed by the agglomeration of multiple primary particles, showing a relatively rounded spherical morphology. "Quasi-secondary particles" refer to those formed by the adhesion of several single particles. Usually, the particle size of a single particle in the above-mentioned quasi-secondary particles is usually between 1um and 5um. In general, the roundness of the particles of "quasi-secondary particles" is lower than that of the above-mentioned conventional "secondary particles".

[0080] It should be specifically noted that the "single crystal positive electrode material" known to those skilled in the art is not a "single crystal" in the strict sense. In crystallography, an ideal single crystal refers to a crystal with completely the same arrangement and orientation. However, due to impurities, strain and crystal defects, ideal single crystals are very rare and difficult to produce in the laboratory. Therefore, the single crystal positive electrode materials known in the art are actually more of a "single crystal morphology" positive electrode material, which only exhibits a large particle size similar to a single crystal in size, as distinguished from a polycrystal composed of many small primary particles.

[0081] In some embodiments, the grain size of the single crystal positive electrode material is D, 150nm<D<250nm. The grain size of the single crystal positive electrode material can specifically be 151nm, 155nm, 160nm, 170nm, 185nm, 190nm, 200nm, 205nm, 230nm or 245nm, etc., which are not limited here. If the grain size of the single crystal positive electrode material is less than 150nm, the cycle stability of the single crystal positive electrode material is poor; if the grain size of the single crystal positive electrode material is greater than 250nm, the capacity and rate performance of the single crystal positive electrode material are poor. Controlling the grain size of the single crystal positive electrode material within the above range is beneficial to improving the electrochemical performance of the single crystal positive electrode material.

[0082] It should be noted that the method for calculating the grain size is generally to use the half-width to calculate it through the Scherrer formula. This method has a premise assumption, that is, the lattice stress is 0, and the broadening of the diffraction peak is entirely caused by the grain size. However, in fact, the lattice stress inside the single crystal positive electrode material cannot be completely ignored. Many factors cause stress concentration inside the single crystal positive electrode material. Therefore, the grain size calculated using the Scherrer formula has its inherent limitations. This application uses the Williamsone-Hall method to separate the diffraction peak broadening caused by the crystallite size and the diffraction peak broadening caused by the lattice stress, so the calculated grain size can better reflect the electrochemical properties of the material.

[0083] In some embodiments, the average particle size D of the single crystal positive electrode material is 50 The particle size of the single crystal positive electrode material is 1.5 μm to 5 μm, and specifically can be 1.5 μm, 1.8 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, etc. Of course, other values ​​within the above range are also possible and are not limited here. Controlling the particle size of the single crystal positive electrode material within the above range is beneficial to improving the structural stability, thermal stability and long cycle stability of the single crystal positive electrode material.

[0084] In some embodiments, the tap density of the single crystal cathode material is greater than 1.5 g / cm 3 , specifically 1.55g / cm 3 、1.58g / cm 3 、1.62g / cm 3 , 1.63g / cm 3 , 1.65g / cm 3 , 1.70g / cm 3 or 1.75g / cm 3 When the tap density of the single crystal positive electrode material is controlled within the above range, it is beneficial to improve the energy density of the battery made of the single crystal positive electrode material.

[0085] In some embodiments, the compaction density of the single crystal cathode material is greater than 3.0 g / cm 3 , specifically 3.1g / cm 3 、3.2g / cm 3 , 3.3g / cm 3 、3.5g / cm 3 、3.7g / cm 3 、3.9g / cm 3 or 4.1 g / cm 3 Of course, it can also be other values ​​within the above range, which is not limited here.

[0086] In the second aspect, the present invention provides a cathode material precursor, the chemical formula of which is Ni a Co b Mn c N d O e , wherein, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, 1≤e≤1.15, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn, and Y;

[0087] The surface area weighted average particle size D[3,2] of the positive electrode material precursor is less than 2.0 μm, and the standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor is less than or equal to 0.05.

[0088] In existing technologies, the reaction between cathode material precursors and lithium salts is limited by ion diffusion rates and temperature gradients, leading to differences in crystal growth rates and unit cell parameters within the material. This can lead to the accumulation of lattice stress within the material. This lattice stress increases the diffusion barrier of Li ions between crystal planes and grain boundaries, reducing the Li ion diffusion coefficient and ultimately increasing the material's DCR. The morphology and structural characteristics of cathode material precursors are highly inherited by the cathode material itself, and therefore the composition and structure of the cathode material precursor have a direct impact on the performance of the final cathode material. The positive electrode material precursor provided in the present application has a surface area weighted average particle size D[3,2]<2.0μm, high reaction activity, and is beneficial to improving the reaction efficiency and mass transfer efficiency in the subsequent preparation process of the positive electrode material from the positive electrode material precursor; at the same time, the standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor obtained by the above preparation method is ≤0.05, indicating that the distribution uniformity of Ni, Co and Mn elements in the positive electrode material precursor is good; using the positive electrode material precursor to prepare the positive electrode material can improve the distribution uniformity of Ni, Co and Mn elements in the positive electrode material, so that the positive electrode material prepared by the positive electrode material precursor has fewer crystal structure defects and smaller lattice stress.

[0089] In some embodiments, the cathode material precursor includes SO4 2- , the SO4 2- The content is η, wherein 0ppm≤η≤1800ppm.

[0090] It is understandable that SO4 on the surface of the precursor 2- It is difficult to decompose and difficult to be doped into the cathode material, so the free SO4 on the surface of the cathode material 2- Content and free SO4 in the precursor 2- The content may be inherited to a certain extent, and the SO4 in the precursor 2- The higher the content, the free SO4 on the surface of the ternary cathode material 2- The higher the content, the free SO4 2- The content is ≤1800ppm, which is more conducive to the preparation of surface free SO4 2- In order to reduce the SO4 in the cathode material precursor, 2- In some embodiments, the Ni salt, Mn salt, Co salt and N salt each independently include at least one of chloride, nitrate, oxalate and acetate, and avoid the use of nickel sulfate, cobalt sulfate and manganese sulfate. Nitrate, chloride, oxalate and acetate of nickel, cobalt and manganese are easily decomposed at high temperature and no obvious residue will be left, so they have little effect on the performance of the positive electrode material. By controlling the SO4 2-The content can even produce SO4 2- The content of SO4 is close to 0. However, this will require a higher purity of the raw materials, which will increase the cost of raw materials. 2- The Ni source, Co source, Mn source and N source in the ternary recycled material of impurities are used as metal sources, and the SO4 2- It is more economical to prepare the cathode material precursor with a certain content.

[0091] In some embodiments, in the metal salt mixed solution, based on the total mass of Ni, Co, and Mn, SO4 2- The content of is ≤1800ppm. Specifically, it can be 500ppm, 800ppm, 1200ppm, 1600ppm, 1700ppm or 1800ppm, etc., which is not limited here.

[0092] In industry, the average particle size D is generally used. 50 The particle size of the cathode material precursor is characterized by the Sauter average particle size, or surface area-weighted average particle size D[3,2], which is the surface area of ​​the cathode material precursor. However, the reaction between the cathode material precursor and the lithium salt is a process that depends on the contact area. Therefore, the Sauter average particle size, or surface area-weighted average particle size D[3,2], is more suitable for characterizing the particle size of the cathode material precursor. The larger D[3,2], the lower the surface activity of the cathode material precursor and the slower the reaction rate with the lithium salt.

[0093] It should be noted that the surface area weighted average particle size D[3,2] of the cathode material precursor in this application can be directly measured by a Malvern 3000 laser particle size analyzer. Specifically, it can be obtained by the following formula: D[3,2]=(∑y 3 N d ) / (∑y 2 N d ) is calculated, where y is the particle size; N d is the number of particles with particle size y.

[0094] Specifically, the surface area weighted average particle size D[3,2] of the positive electrode material precursor can be 1.98 μm, 1.95 μm, 1.8 μm, 1.75 μm, 1.64 μm, 1.5 μm, 1.3 μm, 1.2 μm, 1.1 μm, 0.8 μm, 0.9 μm, or 0.5 μm, etc., without limitation herein. When the surface area weighted average particle size D[3,2] of the positive electrode material precursor is controlled within the above range, the reactivity of the positive electrode material precursor is high, which is beneficial to improving the reaction efficiency and mass transfer efficiency of the positive electrode material precursor during the subsequent sintering process with the lithium source.

[0095] The standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor can be 0.001, 0.005, 0.009, 0.01, 0.013, 0.02, 0.025, 0.03, 0.036, 0.04, 0.044, 0.045, 0.047 or 0.049, etc., which is not limited here.

[0096] In some embodiments, the range of the mass content of each element Ni, Co and Mn in the positive electrode material precursor is ≤0.12, and can be specifically 0.01, 0.015, 0.018, 0.02, 0.029, 0.03, 0.035, 0.048, 0.059, 0.06, 0.08, 0.097, 0.10, 0.105, 0.11, 0.112, 0.115 or 0.119, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0097] It can be understood that the standard deviation and range of the mass content of each element Ni, Co, and Mn in the positive electrode material can reflect the uniformity of the distribution of Ni, Co, and Mn elements in the positive electrode material precursor. The lower the standard deviation and range of the mass content of each element Ni, Co, and Mn, the more uniform the distribution of Ni, Co, and Mn elements in the positive electrode material precursor. At the same time, there is a good inheritance between the distribution uniformity of Ni, Co, and Mn elements in the positive electrode material precursor and the distribution uniformity of Ni, Co, and Mn elements in the single crystal positive electrode material. The more uniform the distribution of Ni, Co, and Mn elements in the positive electrode material precursor, the more uniform the distribution of Ni, Co, and Mn elements in the single crystal positive electrode material made from the positive electrode material precursor.

[0098] Therefore, controlling the standard deviation and range of the mass content of each element Ni, Co and Mn in the positive electrode material precursor within the above range is beneficial to improving the distribution uniformity of Ni, Co and Mn elements in the single crystal positive electrode material, so that the distribution uniformity of Ni, Co and Mn elements in the single crystal positive electrode material is good, the single crystal positive electrode material has fewer crystal structure defects and low lattice strain.

[0099] In some embodiments, the cathode material precursor includes secondary particles, and the secondary particles include a plurality of agglomerated primary particles.

[0100] In some embodiments, the cathode material precursor includes secondary particles, the secondary particles include a plurality of agglomerated primary particles, and the primary particles are spherical.

[0101] In some embodiments, the positive electrode material precursor includes secondary particles, and the secondary particles include a plurality of agglomerated primary particles, and the particle size of the primary particles is 20nm to 1000nm, specifically 20nm, 50nm, 80nm, 100nm, 150nm, 200nm, 500nm, 800nm ​​or 1000nm, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable. When the particle size of the primary particles is greater than 1000nm, the reactivity of the surface of the positive electrode material precursor is poor, the lattice strain of the prepared single crystal positive electrode material is large, and the cycle performance and rate performance of the single crystal positive electrode material are poor. When the primary particles are less than 20nm, the tap density of the positive electrode material precursor is low, resulting in a low tap density of the prepared single crystal positive electrode material. Controlling the particle size of the primary particles within the above range is conducive to improving the cycle performance and rate performance of the single crystal positive electrode material made from the positive electrode material precursor.

[0102] In some embodiments, the average particle size D of the positive electrode material precursor is 50 <3.5 μm, specifically 0.5 μm, 0.8 μm, 1.2 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.2 μm or 3.5 μm, etc., and of course other values ​​within the above range are also possible, which are not limited here. Particle size D of the positive electrode material precursor 50 When controlled within the above range, it is beneficial to improve the reaction activity of the positive electrode material precursor.

[0103] In some embodiments, the specific surface area of ​​the cathode material precursor is ≥5m 2 / g, specifically 5m 2 / g、6m 2 / g、8m 2 / g、10m 2 / g、12m 2 / g、15m 2 / g, 20m 2 / g, 25m 2 / g, 50m 2 / g or 100m 2 / g, etc., and of course, other values ​​within the above range are also possible and are not limited here. The larger the specific surface area of ​​the positive electrode material precursor, the higher the reactivity of the positive electrode material precursor, which is conducive to the reaction between the lithium source and the positive electrode material precursor, and can reduce the lattice defects of the single crystal positive electrode material prepared from the positive electrode material precursor.

[0104] In some embodiments, the tap density of the cathode material precursor is greater than 1 g / cm 3 Specifically, it can be 1.1g / cm 3 , 1.2g / cm 3, 1.3g / cm 3 , 1.8g / cm 3 , 2.3g / cm 3 , 2.5g / cm 3 or 3g / cm 3 When the tap density of the cathode material precursor is controlled within the above range, it is beneficial to increase the tap density of the prepared single crystal cathode material, thereby increasing the energy density of the battery.

[0105] In a third aspect, the present invention provides a method for preparing a single crystal positive electrode material, comprising the following steps:

[0106] Step S100, a mixed solution containing nickel salt, cobalt salt and manganese salt is atomized and then thermally decomposed to obtain a positive electrode material precursor, wherein the surface area weighted average particle size D[3,2] of the positive electrode material precursor is less than 2.0 μm, and the standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor is less than 0.05;

[0107] Step S200: After mixing the positive electrode material precursor with a lithium source, sintering the mixture in an oxygen-containing atmosphere to obtain a positive electrode material, the standard deviation of the mass content of each element Ni, Co and Mn in the single crystal positive electrode material is ≤0.03; the lattice strain of the single crystal positive electrode material is ε, and ε is <0.2%.

[0108] The present application provides a method for preparing a single crystal positive electrode material, wherein a mixed solution containing nickel salt, cobalt salt and manganese salt is subjected to atomization treatment and then thermally decomposed to obtain a positive electrode material precursor. The surface area weighted average particle size D[3,2] of the positive electrode material precursor is less than 2.0 μm, and the reaction activity is high, which is beneficial to improving the reaction efficiency and mass transfer efficiency of the positive electrode material precursor and the lithium source during the subsequent high-temperature sintering process; at the same time, the standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor obtained by the above preparation method is ≤0.05, indicating that the distribution uniformity of Ni, Co and Mn in the positive electrode material precursor is good; furthermore, the single crystal positive electrode material prepared by the above positive electrode material precursor after subsequent sintering with the lithium source has a weighted average particle size D[3,2] less than 2.0 μm, and the reaction activity is high, which is beneficial to improving the reaction efficiency and mass transfer efficiency of the positive electrode material precursor and the lithium source during the subsequent high-temperature sintering process; at the same time, the standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor obtained by the above preparation method is ≤0.05, indicating that the distribution uniformity of Ni, Co and Mn in the positive electrode material precursor is good; furthermore, the weighted average particle size D[3,2] of the positive electrode material precursor is less than 2.0 μm, and the reaction activity is high, which is beneficial to improving the reaction efficiency and mass transfer efficiency of the positive electrode material precursor and the lithium source during the subsequent high-temperature sintering process ... The standard deviation of the mass content of these elements is ≤0.03, and the distribution uniformity of Ni, Co, and Mn elements inside the single crystal positive electrode material is good, which is conducive to reducing the crystal structure defects of the single crystal positive electrode material; and the lattice strain of the single crystal positive electrode material is low, and its lattice strain ε is less than 0.2%, which can reduce the diffusion energy barrier of lithium ions between microcrystals and improve the Li ion diffusion coefficient, so that the single crystal positive electrode material exhibits good rate performance and low DCR; at the same time, low lattice strain can also inhibit the generation of microcracks in the single crystal positive electrode material, thereby improving the cycle performance of the single crystal positive electrode material.

[0109] In step S100, a mixed solution containing nickel salt, cobalt salt and manganese salt is atomized and then thermally decomposed to obtain a positive electrode material precursor, wherein the surface area weighted average particle size D[3, 2] of the positive electrode material precursor is less than 2.0 μm, and the standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor is ≤0.05.

[0110] Specifically, the surface area weighted average particle size D[3,2] of the positive electrode material precursor can be 1.98μm, 1.95μm, 1.8μm, 1.75μm, 1.64μm, 1.5μm, 1.3μm, 1.2μm, 1.1μm, 0.8μm, 0.9μm or 0.5μm, etc., and is not limited here. When the surface area weighted average particle size D[3,2] of the positive electrode material precursor is controlled within the above range, the reaction activity of the positive electrode material precursor is high, which is beneficial to improving the reaction efficiency and mass transfer efficiency of the positive electrode material precursor in the subsequent sintering process with the lithium source. The surface area weighted average particle size D[3,2] of the precursor is mainly related to the pyrolysis temperature. As the pyrolysis temperature increases, the surface area weighted average particle size D[3,2] increases and the reaction activity of the precursor decreases.

[0111] The standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor can be 0.001, 0.005, 0.009, 0.01, 0.013, 0.02, 0.025, 0.03, 0.036, 0.01, 0.044, 0.045, 0.047 or 0.049, etc., which is not limited here.

[0112] In some embodiments, the nickel salt includes at least one of nickel chloride, nickel sulfate, nickel nitrate, nickel carbonate, nickel oxalate, and nickel acetate.

[0113] In some embodiments, the cobalt salt includes at least one of cobalt chloride, cobalt oxalate, cobalt carbonate, cobalt sulfate, cobalt nitrate, and cobalt acetate.

[0114] In some embodiments, the manganese salt includes at least one of manganese chloride, manganese carbonate, manganese sulfate, manganese oxalate, manganese nitrate, and manganese acetate.

[0115] In some embodiments, the molar ratio of Ni, Co, and Mn in the mixed solution is (50-98):(0-20):(0-30), and the content of Co and Mn in the mixed solution is not 0. The molar ratio of Ni, Co, and Mn in the mixed solution can be 50:0.1:0.1, 60:10:30, 65:15:20, 65:5:30, 70:5:25, 70:10:20, 80:5:15, 85:10:5, or 98:1:1, etc., and is not limited here.

[0116] In some embodiments, the total metal concentration in the mixed solution is 200 g / L to 500 g / L, specifically 200 g / L, 220 g / L, 260 g / L, 300 g / L, 350 g / L, 400 g / L, 450 g / L, 480 g / L, or 500 g / L, etc., and other values ​​within the above range are also possible. The applicant has found that the metal concentration in the mixed solution can affect the preparation efficiency of the precursor and the degree of thermal decomposition reaction. When the metal concentration of the mixed liquid is too high, it may lead to incomplete precursor reaction, which will not only cause structural instability but also make the uniformity of particle element distribution unsatisfactory. When the metal concentration of the mixed liquid is too low, not only the preparation efficiency is low, but also the mixed liquid is prone to produce more hollow spherical particles and breakage when it evaporates rapidly at high temperature, which leads to unsatisfactory particle size distribution. There may even be more micropowder particles that affect the performance of the material, while a relatively small number of large particles are also produced. Large particles are more likely to cause uneven element distribution and affect the surface area weighted average particle size D of the single crystal positive electrode material precursor [3, 2].

[0117] In some embodiments, the mixed solution further includes a dopant containing N element, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y.

[0118] In some embodiments, the mixed solution further includes an ultrasonic stirring step before the atomization treatment, and the ultrasonic stirring includes placing the mixed solution in a reactor with ultrasonic stirring function for heating and ultrasonic stirring.

[0119] In some embodiments, the ultrasonic stirring temperature is 50°C to 70°C.

[0120] In some embodiments, the ultrasonic stirring has an ultrasonic frequency of 30 KHz-50 KHz, and an ultrasonic stirring time of 0.5 h-2 h.

[0121] Heating and ultrasonic stirring before atomization can further fully mix the chemical elements in the mixed liquid and quickly obtain more uniform droplets, so that the elements on the surface of the precursor particles are more evenly distributed during thermal decomposition and have a smaller standard deviation mean value of the mass content.

[0122] In some embodiments, a surfactant is added to the mixed solution before atomization, and the surfactant includes polyethylene glycol.

[0123] It can be understood that when polyethylene glycol is dissolved in water and reaches a certain concentration, it will reduce the surface tension of the system, making the overall particle size of the cathode material precursor smaller, the element distribution more uniform, and reducing the surface area weighted average particle size D of the single crystal cathode material precursor [3, 2].

[0124] In some embodiments, the surfactant comprises 0.5% to 5% of the total mass of the mixed solution. Within this range, the surfactant can stably produce precursor particles with smooth, uniform morphology and good dispersion. A low concentration of the surfactant will not significantly affect its effect, while a high concentration will not only affect the overall concentration of the mixture but also lead to the precipitation of Ni, Co, and Mn metal ions.

[0125] In some embodiments, the mixed solution further includes an ultrasonic stirring step before atomization treatment, wherein the mixed solution is placed in a reactor with ultrasonic stirring function and heated to 50°C to 70°C, while adjusting the ultrasonic stirring frequency to 30-50KHz. After ultrasonic stirring in the reactor for 0.5h-2h, the heating function is turned off and 0.5%-5% of the total mass of the mixed solution is added with polyethylene glycol, and then ultrasonic stirring is continued for 0.5h-1h. In some embodiments, the chemical formula of the positive electrode material precursor is Ni a Co b Mn c N d O e , wherein, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, 1≤e≤1.15, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y.

[0126] In some embodiments, the range of the mass content of each element Ni, Co and Mn in the positive electrode material precursor is ≤0.12, and can be specifically 0.01, 0.015, 0.018, 0.02, 0.029, 0.03, 0.035, 0.048, 0.059, 0.06, 0.08, 0.097, 0.10, 0.105, 0.11, 0.112, 0.115 or 0.119, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0127] It can be understood that the standard deviation and range of the mass content of each element Ni, Co, and Mn in the positive electrode material can reflect the uniformity of the distribution of Ni, Co, and Mn elements in the positive electrode material precursor. The lower the standard deviation and range of the mass content of each element Ni, Co, and Mn, the more uniform the distribution of Ni, Co, and Mn elements in the positive electrode material precursor. At the same time, there is a good inheritance between the distribution uniformity of Ni, Co, and Mn elements in the positive electrode material precursor and the distribution uniformity of Ni, Co, and Mn elements in the single crystal positive electrode material. The more uniform the distribution of Ni, Co, and Mn elements in the positive electrode material precursor, the more uniform the distribution of Ni, Co, and Mn elements in the single crystal positive electrode material made from the positive electrode material precursor.

[0128] Controlling the standard deviation and range of the mass content of each element Ni, Co and Mn in the positive electrode material precursor within the above range is beneficial to improving the distribution uniformity of Ni, Co and Mn elements in the single crystal positive electrode material, so that the distribution uniformity of Ni, Co and Mn elements in the single crystal positive electrode material is good, the crystal structure defects of the single crystal positive electrode material are few, and the lattice strain is low.

[0129] In some embodiments, the flow rate of the mixed solution is 100L / h to 900L / h, specifically 100L / h, 200L / h, 300L / h, 400L / h, 500L / h, 600L / h, 700L / h, 800L / h or 900L / h, etc., which are not limited here. The higher the flow rate of the mixed solution, the faster the synthesis speed of the precursor, but the uniformity of the Ni / Co / Mn distribution deteriorates. When the flow rate is lower than 100L / h, the synthesis efficiency of the precursor is low and the preparation cost is high; when the flow rate of the mixed solution is higher than 900L / h, the standard deviation and variance of the mass content of each element Ni, Co and Mn in the precursor increase significantly, resulting in a decrease in the distribution uniformity of Ni, Co and Mn elements in the prepared single crystal positive electrode material and an increase in lattice strain.

[0130] In some embodiments, the pressure of the atomization treatment is 0.4 MPa to 0.8 MPa, specifically 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.75 MPa or 0.8 MPa, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0131] In some embodiments, the thermal decomposition temperature is between 500°C and 850°C, specifically 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, or 800°C, but is not limited to the listed values; other values ​​within this numerical range are also applicable. As the thermal decomposition temperature increases, the surface area weighted average particle size D[3,2] of the positive electrode material precursor decreases, resulting in a decrease in precursor activity. When the thermal decomposition temperature is higher than 850°C, the surface area weighted average particle size D[3,2] of the positive electrode material precursor is greater than 2.0 μm; at this point, the positive electrode material precursor has poor reactivity, resulting in a large number of defects in the subsequently prepared single crystal positive electrode material, a lattice strain ε exceeding 0.2%, and poor rate performance, a high DCR, and low cycling performance of the single crystal positive electrode material. Therefore, appropriately lowering the thermal decomposition temperature of the precursor is beneficial to increasing the precursor's reactivity and improving the rate and DCR of the positive electrode material. However, when the pyrolysis temperature is lower than 500 °C, the metal salts of Ni, Co, and Mn are not completely decomposed, resulting in the precursor Cl - 、NO3 - 、CO3 2-If the anion content is too high, these residual anions will inhibit the formation of single crystals and corrode the sintering kiln in the subsequent preparation of positive electrode materials.

[0132] Step S200: After mixing the positive electrode material precursor with a lithium source, sintering the mixture in an oxygen-containing atmosphere to obtain a positive electrode material, the standard deviation of the mass content of each element Ni, Co and Mn in the single crystal positive electrode material is ≤0.03; the lattice strain of the single crystal positive electrode material is ε, and ε is <0.2%.

[0133] In some embodiments, the lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium sulfate, lithium chloride, lithium nitrate, and lithium oxalate.

[0134] In some embodiments, the molar ratio of lithium in the lithium source to the sum of nickel, cobalt and manganese in the positive electrode material precursor is 0.98 to 1.10, specifically 0.98, 0.99, 1.01, 1.03, 1.05, 1.06, 1.08, 1.09 or 1.10, etc., and of course it can also be other values ​​within the above range, which is not limited here.

[0135] In some embodiments, the sintering reaction temperature is 750°C to 950°C, specifically 750°C, 760°C, 780°C, 800°C, 850°C, 900°C, 920°C, or 950°C, etc., and other values ​​within the above range are also possible and are not limited here. The sintering temperature is closely related to the Ni content. The higher the Ni content, the lower the sintering temperature. In addition, a suitable sintering temperature is conducive to reducing crystal structure defects and lattice strain, thereby improving the electrochemical performance of the single crystal positive electrode material.

[0136] In some embodiments, the sintering reaction time is 10 h to 30 h, specifically 10 h, 12 h, 15 h, 16 h, 18 h, 20 h, 24 h, 28 h or 30 h, etc. Of course, it can also be other values ​​within the above range, which is not limited here.

[0137] In a fourth aspect, an embodiment of the present application provides a lithium-ion battery, wherein the lithium-ion battery includes the single crystal positive electrode material described in the first aspect or the positive electrode material prepared by the preparation method of the single crystal positive electrode material described in the third aspect.

[0138] The beneficial effects of the present application will be further illustrated below with reference to examples and comparative examples.

[0139] Example 1

[0140] (1) Molar ratio (n Ni :n Co :n Mn=0.67:0.05:0.28) nickel chloride, cobalt chloride, and manganese chloride were weighed and added to water to prepare a mixed solution. The total metal concentration in the mixed solution was controlled to be 300 g / L. The mixed solution was placed in a reactor with ultrasonic stirring function and heated to 60° C. The ultrasonic stirring frequency was adjusted to 33 kHz. After ultrasonic stirring in the reactor for 1 hour, the heating function was turned off and polyethylene glycol (1% by weight of the total weight of the mixed solution) was added, and ultrasonic stirring was continued for another 0.5 hour. Based on the total weight of Ni, Co, and Mn elements, SO4 2- The content is 900ppm.

[0141] (2) After the mixed solution is atomized into droplets, it is placed in an air atmosphere and thermally decomposed at 650° C. in a roasting furnace; the flow rate of the mixed solution is controlled to be 200 L / h and the atomization pressure is controlled to be 0.6 MPa.

[0142] (3) The thermal decomposition product is subjected to air flow pulverization to obtain a positive electrode material precursor (Ni 0.67 Co 0.05 Mn 0.28 O).

[0143] (4) Molar ratio (n Ni+Co+Mn :n Li =1:1) The cathode material precursor and lithium carbonate were weighed and mixed evenly, and then placed in an oxygen atmosphere and heated to 920° C. and sintered for 20 h to obtain a single crystal cathode material.

[0144] The single crystal cathode material prepared in this embodiment has the general chemical formula of LiNi 0.67 Co 0.05 Mn 0.28 O2, the average particle size D of the single crystal cathode material 50 The tap density is 3.8 μm and 1.95 g / cm 3 .

[0145] Figure 1 is an SEM morphology image of the positive electrode material precursor prepared in Example 1 of the present application, and Figure 2 is another SEM morphology image of the positive electrode material precursor prepared in Example 1 of the present application. As shown in Figures 1 and 2, the positive electrode material precursor includes secondary particles, and the secondary particles include multiple agglomerated primary particles.

[0146] When observing the cathode material precursor prepared in Example 1 of the present application with a scanning electron microscope, 10 points of the cathode material precursor were randomly selected at a magnification of 3K to perform EDS point scanning to test the Ni, Co, and Mn contents. In the EDS spectrum results of the cathode material precursor, as shown in FIG3 , the range of Ni content in the cathode material precursor is 0.095, and the standard deviation is 0.036; the range of Co content is 0.029, and the standard deviation is 0.009; the range of Mn content is 0.081, and the standard deviation is 0.030. This shows that the cathode material precursor prepared in Example 1 has good distribution uniformity of Ni, Co, and Mn. In addition, through ion chromatography detection, the free SO4 on the surface of the precursor is 0.095. 2- The content is 504ppm.

[0147] Figure 4 shows the Williamsone-Hall analysis fitting curve for the single-crystalline cathode material prepared in Example 1 of the present application. As shown in Figure 4 , analysis and calculation of the data in Figure 4 indicate that the lattice strain of the single-crystalline cathode material is 0.11%. Other performance parameters of the cathode material precursor and the single-crystalline cathode material are detailed in Tables 1 and 2.

[0148] Example 2

[0149] The difference from Example 1 is that (2) after the mixed solution is atomized into droplets, it is placed in an air atmosphere and thermally decomposed at 750°C in a roasting furnace; the flow rate of the mixed solution is controlled to be 200L / h and the atomization pressure is 0.6MPa.

[0150] The single crystal cathode material prepared in this embodiment has the general chemical formula of LiNi 0.67 Co 0.05 Mn 0.28 The average particle size D50 of the single crystal positive electrode material is 3.7 μm, and the tap density is 1.85 g / cm 3 .

[0151] Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0152] Example 3

[0153] The difference from Example 1 is that (2) after the mixed solution is atomized into droplets, it is placed in an air atmosphere and thermally decomposed at 650°C in a roasting furnace; the flow rate of the mixed solution is controlled to be 100L / h and the atomization pressure is 0.6MPa.

[0154] The single crystal positive electrode material prepared in this embodiment has the general chemical formula of LiNi 0.67 Co 0.05 Mn 0.28The average particle size D50 of the single crystal positive electrode material is 4.0 μm, and the tap density is 2.12 g / cm 3 .

[0155] Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0156] Example 4

[0157] The difference from Example 1 is that (2) after the mixed solution is atomized into droplets, it is placed in an air atmosphere in a roasting furnace for thermal decomposition at 500°C; the flow rate of the mixed solution is controlled to be 500L / h, and the atomization pressure is 0.6MPa.

[0158] The single crystal positive electrode material prepared in this embodiment has the general chemical formula of LiNi 0.67 Co 0.05 Mn 0.28 The average particle size D50 of the single crystal positive electrode material is 3.8 μm, and the tap density is 1.90 g / cm 3 .

[0159] Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0160] Example 5

[0161] The difference from Example 1 is that (4) in molar ratio (n Ni+Co+Mn :n Li =1:1) The cathode material precursor and lithium carbonate were weighed and mixed evenly, and then placed in an oxygen atmosphere and heated to 950° C. and sintered for 20 h to obtain a single crystal cathode material.

[0162] The single crystal positive electrode material prepared in this embodiment has the general chemical formula of LiNi 0.67 Co 0.05 Mn 0.28 The average particle size D50 of the single crystal positive electrode material is 4.5 μm, and the tap density is 2.2 g / cm 3 .

[0163] Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0164] Example 6

[0165] The difference from Example 1 is that (4) in molar ratio (n Ni+Co+Mn :n Li =1:1) The cathode material precursor and lithium carbonate were weighed and mixed evenly, and then placed in an oxygen atmosphere and heated to 900° C. and sintered for 20 h to obtain a single crystal cathode material.

[0166] The single crystal cathode material prepared in this embodiment has the general chemical formula of LiNi 0.67 Co 0.05 Mn 0.28 The average particle size D50 of the single crystal positive electrode material is 3.0 μm, and the tap density is 1.68 g / cm 3 .

[0167] Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0168] Example 7

[0169] (1) Molar ratio (n Ni :n Co :n Mn =0.88:0.06:0.04) Weigh nickel chloride, cobalt chloride, and manganese chloride and add them to water to prepare a mixed solution. The total metal concentration in the mixed solution is controlled to be 300 g / L. Based on the total mass of Ni, Co, and Mn elements, SO4 2- The content is ≤1780ppm.

[0170] (2) After the mixed solution is atomized into droplets, it is placed in an air atmosphere in a roasting furnace for thermal decomposition at 600°C; the flow rate of the mixed solution is controlled to be 200 L / h and the atomization pressure is controlled to be 0.6 MPa.

[0171] (3) The thermal decomposition product is subjected to air flow pulverization to obtain a positive electrode material precursor (Ni 0.88 Co 0.06 Mn 0.04 O).

[0172] (4) Molar ratio (n Ni+Co+Mn :n Li =1:1) The cathode material precursor and lithium carbonate were weighed and mixed evenly, and then placed in an oxygen atmosphere and heated to 850° C. and sintered for 15 h to obtain a single crystal cathode material.

[0173] The single crystal cathode material prepared in this embodiment has the general chemical formula of LiNi 0.88 Co 0.06 Mn 0.04 The average particle size D50 of the single crystal positive electrode material is 3.2 μm, and the tap density is 1.77 g / cm 3 .

[0174] Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0175] Example 8

[0176] (1) Molar ratio (n Ni :n Co :nMn :n Al =0.88:0.06:0.03:0.03) nickel chloride, cobalt chloride, manganese chloride, and aluminum chloride were weighed and added to water to form a mixed solution, and the total metal concentration in the mixed solution was controlled to be 300 g / L.

[0177] (2) After the mixed solution is atomized into droplets, it is placed in an air atmosphere in a roasting furnace for thermal decomposition at 600°C; the flow rate of the mixed solution is controlled to be 200 L / h and the atomization pressure is controlled to be 0.6 MPa.

[0178] (3) The thermal decomposition product is subjected to air flow pulverization to obtain a positive electrode material precursor (Ni 0.88 Co 0.06 Mn 0.03 Al 0.03 O).

[0179] (4) Molar ratio (nNi+Co+Mn+Al:n Li =1:1) The cathode material precursor and lithium hydroxide were weighed and mixed evenly, and then placed in an oxygen atmosphere and heated to 850° C. and sintered for 15 h to obtain a cathode material.

[0180] The single crystal cathode material prepared in this embodiment has the general chemical formula of LiNi 0.88 Co 0.06 Mn 0.03 Al 0.03 The average particle size D50 of the single crystal positive electrode material is 3.2 μm, and the tap density is 1.78 g / cm 3 .

[0181] Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0182] Example 9

[0183] The difference from Example 1 is that (1) based on the total mass of Ni, Co, and Mn elements, SO4 2- The content of free SO4 on the surface of the precursor prepared in this embodiment was 200ppm. 2- The content of the single crystal positive electrode material prepared in this embodiment has the general chemical formula of LiNi 0.67 Co 0.05 Mn 0.28 O2, the average particle size D of the single crystal cathode material 50 The tap density is 3.8 μm and 1.95 g / cm 3 Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0184] Example 10

[0185] The difference from Example 1 is that (1) in molar ratio (n Ni :n Co :n Mn = 0.67:0.05:0.28) nickel chloride, cobalt chloride, and manganese chloride were weighed and added to water to prepare a mixed solution. The total metal concentration in the mixed solution was controlled to be 500 g / L, and polyethylene glycol was added at 5% of the total mass of the mixed solution. Based on the total mass of Ni, Co, and Mn elements, SO4 2- The content is 900ppm.

[0186] The single crystal positive electrode material prepared in this embodiment has the general chemical formula of LiNi 0.67 Co 0.05 Mn 0.28 The average particle size D50 of the single crystal positive electrode material is 3.8 μm, and the tap density is 1.83 g / cm 3 Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0187] Example 11

[0188] The difference from Example 1 is that (1) in molar ratio (n Ni :n Co :n Mn =0.67:0.05:0.28) nickel chloride, cobalt chloride, and manganese chloride were weighed and added to water to prepare a mixed solution. The total metal concentration in the mixed solution was controlled to be 200 g / L. The mixed solution was placed in a reactor with ultrasonic stirring function and heated to 60°C. The ultrasonic stirring frequency was adjusted to 33 kHz. Ultrasonic stirring was carried out in the reactor for 1 hour. Based on the total mass of Ni, Co, and Mn elements, SO4 2- The content is 900ppm.

[0189] The single crystal positive electrode material prepared in this embodiment has the general chemical formula of LiNi 0.67 Co 0.05 Mn 0.28 The average particle size D50 of the single crystal positive electrode material is 4.1 μm, and the tap density is 1.82 g / cm 3 Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0190] Comparative Example 1

[0191] The difference from Example 1 is that (2) after the mixed solution is atomized into droplets, it is placed in an air atmosphere in a roasting furnace at 880°C for thermal decomposition; the flow rate of the mixed solution is controlled to be 200L / h, and the atomization pressure is 0.6MPa.

[0192] The single crystal positive electrode material prepared in this comparative example has the general chemical formula of LiNi 0.67 Co 0.05 Mn 0.28 O2, the average particle size D50 of the positive electrode material is 3.82μm, and the tap density is 1.86g / cm 3 .

[0193] Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0194] Comparative Example 2

[0195] The difference from Example 1 is that (2) after the mixed solution is atomized into droplets, it is placed in an air atmosphere in a roasting furnace for thermal decomposition at 650°C; the flow rate of the mixed solution is controlled to be 1000L / h and the atomization pressure is 0.6MPa.

[0196] The single crystal positive electrode material prepared in this comparative example has the general chemical formula of LiNi 0.67 Co 0.05 Mn 0.28 The average particle size D50 of the single crystal positive electrode material is 3.72 μm, and the tap density is 1.90 g / cm 3 .

[0197] Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0198] Comparative Example 3

[0199] The difference from Example 1 is that (4) in molar ratio (n Ni+Co+Mn :n Li =1:1) The cathode material precursor and lithium carbonate were weighed and mixed evenly, and then placed in an oxygen atmosphere and heated to 700° C. and sintered for 20 h to obtain a cathode material.

[0200] The positive electrode material prepared in this comparative example is a polycrystalline positive electrode material, and its general chemical formula is LiNi 0.67 Co 0.05 Mn 0.28 The average particle size D50 of the polycrystalline positive electrode material is 3.2 μm, and the tap density is 1.8 g / cm 3 .

[0201] Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0202] Comparative Example 4

[0203] Prepare Ni with reference to CN113488642A Example 2 0.88 Co 0.06 Mn 0.03Al 0.03 (OH)2 quaternary precursor and corresponding positive electrode materials.

[0204] (1) preparing a first solution: nickel sulfate hexahydrate, manganese sulfate monohydrate, and cobalt sulfate heptahydrate were weighed according to a molar ratio of nickel:cobalt:manganese = 0.88:0.06:0.03, and dissolved in deionized water to prepare a transition metal salt solution with a mass concentration of 2 mol / L, referred to as the first solution;

[0205] (2) Prepare the second solution: weigh aluminum nitrate nonahydrate and dissolve it in deionized water. Then, add concentrated ammonia water with a mass concentration of 25% dropwise to the aluminum salt solution while stirring continuously. When the pH reaches 8-9, stop adding concentrated ammonia water. Finally, adjust the volume to a concentration of aluminum hydroxide of 0.11 mol / L. This is called the second solution.

[0206] (3) Preparation of quaternary transition metal hydroxide precursor: Add ammonia water base liquid to the reactor in advance, control the temperature of the reaction system to 55 ° C, and adjust the stirring blade speed to 1000 rpm. Use metering pump No. 1 to add the first solution to the reactor at a rate of 35L / h, use metering pump No. 2 to add the second solution to the reactor at a rate of 20L / h, use metering pump No. 3 to add ammonia solution to keep the ammonia concentration in the system at 0.5mol / L, use metering pump No. 4 to add 4mol / L sodium hydroxide solution, and control the pH of the reaction system to 10.0±0.5. Continue to add materials for 17 hours, and after aging for 10 hours, filter and wash the final precipitated product, dry it in an oven at 110 ° C for 12 hours, and crush and sieve to obtain Ni 0.88 Co 0.06 Mn 0.03 Al 0.03 (OH)2 hydroxide precursor.

[0207] (4) The hydroxide precursor and lithium hydroxide were mixed evenly in a molar ratio of 1:1.05, sintered at 500 ° C for 3 h and 850 ° C for 15 h in an oxygen atmosphere, and after cooling, the product was crushed and sieved to a D50 of 12 μm to obtain a single crystal positive electrode material LiNi 0.88 Co 0.06 Mn 0.03 Al 0.03 O2.

[0208] Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0209] Comparative Example 5

[0210] Reference CN116230922A to prepare Ni 0.8 Co 0.1 Mn 0.1 (OH)2 precursor and corresponding cathode materials.

[0211] (1) NiSO4, CoSO4, and MnSO4 were mixed in a Ni / Co / Mn molar ratio of 0.8:0.1:0.1 to prepare a solution.

[0212] (2) The solution was added to a reactor at 55°C, and NaOH and NH3·H2O were used as precipitants and chelating agents for co-precipitation reaction for 36 hours to obtain Ni 0.8 Co 0.1 Mn0.1(OH)2 precursor.

[0213] (3) The precursor was dried at 80°C for 12 hours and then dried again at 110°C for 12 hours.

[0214] (4) The precursor and lithium hydroxide were added to a dry high-speed mixer at a molar ratio of 1:1.05 and mixed for 5 minutes.

[0215] (5) The temperature was raised to 950°C at a rate of 2°C / min and maintained at 950°C for 5 hours, then naturally cooled to 900°C and maintained for 5 hours. Oxygen was continuously passed at a flow rate of 10 mL / min during the heating and holding period. After the calcination was completed, the mixture was naturally cooled to room temperature and crushed and classified to prepare LiNi 0.8 Co 0.1 Mn 0.1 Single crystal positive electrode material for O2.

[0216] Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0217] Comparative Example 6

[0218] The difference from Example 1 is that (1) based on the total mass of Ni, Co, and Mn elements, SO4 2- The content is 2000ppm.

[0219] The free SO4 on the surface of the precursor prepared in this example 2- The content of the single crystal positive electrode material prepared in this embodiment has the general chemical formula of LiNi 0.67 Co 0.05 Mn 0.28 O2, the average particle size D of the single crystal cathode material 50 The tap density is 3.8 μm and 1.95 g / cm 3 Other performance parameters of the cathode material precursor and single crystal cathode material are detailed in Table 1 and Table 2.

[0220] Test method:

[0221] (1) Under a magnification of 3K, an energy dispersive X-ray spectrometer (EDS) attached to a scanning electron microscope was used to randomly select 10 points on the surface of the untreated cathode material precursor or single crystal cathode material to scan and test the Ni, Co, and Mn contents of the cathode material precursor or single crystal cathode material. The standard deviation and range of the mass content of each element Ni, Co, and Mn were calculated to characterize the uniformity of the distribution of Ni, Co, and Mn elements.

[0222] (2) The surface area weighted average particle size D[3, 2] of the cathode material precursor was obtained by using a Malvern 3000 laser particle size analyzer.

[0223] (3) The lattice strain and grain size of the single crystal cathode material are calculated from the XRD data by Williamsone-Hall analysis:

[0224] The specific method is: using Japan Rigaku X-ray diffractometer to measure, the specific conditions are: 0.75 degrees / minute, step size 0.02, continuous scanning between 10 and 90 degrees in the 2θ range. hkl is the horizontal axis, β hkl cosθ hkl As the ordinate, the curve is drawn and linearly fitted. The strain ε and grain size D can be calculated by the slope and intercept. It is worth mentioning that the half-peak width β used in the fitting hkl It is necessary to eliminate the influence of the instrument, that is, β hkl =β 总 -β 仪器 , where β 总 is the half-peak width of the actual test, β 仪器 The half-peak width broadening caused by the instrument can be obtained by XRD calculation of the standard silicon wafer. 仪器 In addition, the data of seven strong diffraction peaks (003), (101), (102), (104), (015), (107), and (113) were selected for fitting to improve the degree of linear fitting and reduce the actual test error.

[0225] where β is the half-width at half maximum, θ is the diffraction angle, both in radians; k is a constant, equal to 0.89; λ is the X-ray wavelength, equal to 0.154 nm; D is the grain size, in nm; and ε is the lattice strain, dimensionless.

[0226] (4) Using a vibrator, weigh a certain amount of sample and vibrate 3000 times at 300 times / min to test the tap density.

[0227] (5) Electrochemical performance test:

[0228] The electrochemical performance of the material was evaluated using a coin-shaped half-cell. The following steps were used: Single-crystal cathode material, conductive carbon black, and PVDF were weighed in a 93:5:2 mass ratio. N-methyl-2-pyrrolidone (NMP) was added to a 50% solids content. The mixture was dispersed in a high-speed disperser to form a viscous slurry. The slurry was evenly coated onto aluminum foil using a spatula. After drying in an 80°C oven, the slurry was rolled and cut into 14mm diameter cathode sheets. A 16mm lithium sheet was used as the anode sheet, a Celgard polypropylene film was used as the separator, and a 1 mol / L LiPF6 carbonate solution was used as the electrolyte. The coin-shaped half-cell was assembled in an argon-filled glove box. Capacity and cycling performance were tested using a LAND battery testing system at 25°C and 3.0-4.3V. The nominal capacity at 1C was set to 200mAh / g. In addition, the voltage UA at the beginning of each week's discharge and the voltage data UB at the 60th second, the discharge current IDis, and the calculation formula of the DC internal resistance are DCR=(U A -U B ) / I Dis .

[0229] (6) SO4 2- Content test:

[0230] Take 0.5 g and dissolve it in 50 ml of water, ultrasonicate for 5 min and filter, and measure SO4 in the filtrate by ion chromatography (Thermo Fisher ion chromatograph ICS6000 HPIC). 2- Ion content.

[0231] (7) Electron backscatter diffraction (EBSD) test:

[0232] The cathode material samples were first embedded in a carbon lacquer (PELCO) graphite block, and then the cross-section of the block was polished using an argon ion beam. Electron backscatter diffraction (EBSD) imaging was performed using a JEOL JSM-7000F scanning electron microscope. The EBSD image was set to a step size of 250 nm (each pixel was 250 nm × 250 nm).

[0233] The above test results are detailed in Tables 1 to 3.

[0234] Table 1 Performance parameter results of positive electrode material precursors prepared in various embodiments and comparative examples

[0235] Table 2 Performance parameter results of single crystal positive electrode materials prepared in various embodiments and comparative examples

[0236] Table 3 Electrochemical performance test results of single crystal positive electrode materials prepared in various embodiments and comparative examples

[0237] According to the test data in Tables 1 to 3, the standard deviation of the mass content of each element Ni, Co and Mn in the single crystal positive electrode materials prepared in Examples 1 to 8 is ≤0.03, and the range of the mass content of each element Ni, Co and Mn is ≤0.08, indicating that the distribution uniformity of Ni, Co and Mn elements inside the single crystal positive electrode material is good, which is conducive to reducing the crystal structure defects of the single crystal positive electrode material; the lattice strain ε of the single crystal positive electrode material is less than 0.2%, which can reduce the diffusion energy barrier of lithium ions between crystallites and increase the Li ion diffusion coefficient, so that the single crystal positive electrode material exhibits good rate performance and low DCR; at the same time, low lattice strain can also inhibit the generation of microcracks in the single crystal positive electrode material, thereby improving the cycle performance of the single crystal positive electrode material.

[0238] According to the data in Tables 1 and 2, there is a good inheritance between the distribution uniformity of Ni, Co, and Mn elements in the cathode material precursor and the distribution uniformity of Ni, Co, and Mn elements in the single crystal cathode material. The smaller the range and standard deviation of the mass content of each element Ni, Co, and Mn in the cathode material precursor, the smaller the range and standard deviation of the mass content of each element Ni, Co, and Mn in the single crystal cathode material. In addition, the range and standard deviation of the Ni, Co, and Mn content in the single crystal cathode material are always smaller than those in the precursor. This is because high-temperature sintering is required during the preparation of the single crystal cathode material, and the metal ions will further diffuse, thereby improving the distribution uniformity of the Ni, Co, and Mn elements.

[0239] According to the test data in Tables 1 to 3, the single crystal positive electrode material prepared in Example 1 has the best comprehensive performance.

[0240] Comparing Example 1 and Example 2, the single crystal positive electrode material of Example 1 exhibits good rate performance, low impedance, and high cycle performance. This is because when preparing the positive electrode material precursor in Example 1, the temperature of the atomized mixed solution for thermal decomposition is appropriate, resulting in a low surface area weighted average particle size D[3,2] of the positive electrode material precursor, high reactivity of the positive electrode material precursor, reduced crystal structure defects of the single crystal positive electrode material, and low lattice strain of the single crystal positive electrode material. Therefore, the single crystal positive electrode material prepared in Example 1 exhibits better rate performance, lower impedance, and better cycle performance.

[0241] Compared to Example 1, in Example 5, the sintering temperature was increased during the sintering of the cathode material precursor and the lithium source. This resulted in lower ranges and standard deviations in the mass content of each element, Ni, Co, and Mn, in the single-crystalline cathode material. The lattice strain ε of the single-crystalline cathode material was also reduced, resulting in improved cycling performance. However, due to the significantly larger grain size of the single-crystalline cathode material and the longer Li ion diffusion path, the rate performance of the single-crystalline cathode material prepared in Example 5 was lower than that of Example 1.

[0242] Compared with Example 1, in Example 6, during the sintering process of the positive electrode material precursor and the lithium source, the sintering temperature is lowered, which makes the grain size of the single crystal positive electrode material smaller and the lattice strain ε increases. Therefore, the cycle stability of the single crystal positive electrode material of Example 6 is lower than that of the single crystal positive electrode material of Example 1.

[0243] Compared with Example 1, the free SO4 2- The content is reduced, showing better rate and cycle performance.

[0244] Compared with Example 1, Example 10 does not perform ultrasonic stirring before atomizing the single crystal positive electrode material precursor mixed liquid, and the range and standard deviation of the mass content of each element Ni, Co and Mn in the single crystal positive electrode precursor are higher, which affects its circulation and internal resistance.

[0245] Compared with Example 1, in Example 11, polyethylene glycol is not added to the single crystal positive electrode material precursor mixture for ultrasonic stirring before atomization. The surface area weighted average particle size D[3, 2] of the single crystal positive electrode material is relatively large, and large agglomerated particles may appear. In addition, the range and standard deviation of the mass content of each element Ni, Co and Mn in the single crystal positive electrode precursor are higher, which affects its circulation and internal resistance.

[0246] Compared with Example 1, the free SO4 2- More than 1000ppm. Excessive SO4 2- This results in deterioration of material capacity, rate and cycle performance.

[0247] Compared with Example 1, Comparative Example 1 increases the thermal decomposition temperature during the preparation of the positive electrode material precursor, so that the surface area weighted average particle size D[3, 2] of the positive electrode material precursor is greater than 2.0 μm; the reaction activity of the positive electrode material precursor is poor, resulting in more defects in the subsequently prepared single crystal positive electrode material, and the lattice strain ε exceeds 0.2%, which makes the single crystal positive electrode material exhibit poor rate performance, high DCR and low cycle performance.

[0248] Compared with Example 1, the atomization flow rate is increased during the preparation of the precursor of the positive electrode material of Comparative Example 2, and the standard deviation and variance of the mass content of each element Ni, Co and Mn in the prepared positive electrode material precursor are significantly increased, resulting in a decrease in the distribution uniformity of Ni, Co and Mn elements in the prepared single crystal positive electrode material, an increase in the lattice strain, and an increase in the lattice strain ε exceeding 0.2%. Therefore, the rate performance and cycle performance of the single crystal positive electrode material prepared in Comparative Example 2 are both reduced.

[0249] Compared to Example 1, the cathode material of Comparative Example 3 exhibited a polycrystalline structure due to excessively low sintering temperature during the sintering of the precursor and lithium source. This cathode material had a grain size below 150 nm and exhibited good rate performance. However, the lattice strain exceeded 0.2%, making it susceptible to cracking and pulverization during cycling, reducing the structural stability of the cathode material and significantly reducing its cycling capacity.

[0250] Compared with Example 1, the standard deviation and variance of the mass content of each element Ni, Co and Mn in the positive electrode material precursor of Comparative Example 4 are significantly greater than those in Example 1. Therefore, the lattice strain of the prepared single crystal positive electrode material is significantly increased, and the lattice strain exceeds 0.2%, resulting in a significant decrease in the rate performance and cycle performance of the single crystal positive electrode material.

[0251] Similarly, in the single crystal positive electrode material prepared in Comparative Example 5, the surface area weighted average particle size D[3, 2] of the positive electrode material precursor is too large, and the standard deviation and variance of the mass content of each element Ni, Co and Mn in the positive electrode material precursor are significantly greater than those in Example 1. Therefore, the lattice strain of the prepared single crystal positive electrode material is significantly increased, and the lattice strain exceeds 0.2%, resulting in a significant decrease in the rate performance and cycle performance of the positive electrode material.

[0252] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A single crystal positive electrode material, characterized in that: The chemical formula of the single crystal positive electrode material is Li x Ni a Co b Mn c N d O2, wherein 0.98≤x≤1.1, 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; When observing the single crystal positive electrode material with a scanning electron microscope, at a magnification of 3K, 10 points of the single crystal positive electrode material are randomly selected for EDS point scanning to test the Ni, Co, and Mn contents. In the EDS spectrum results of the single crystal positive electrode material, the standard deviation of the mass content of each element of Ni, Co, and Mn in the single crystal positive electrode material is ≤0.03; The lattice strain of the single crystal positive electrode material is ε, and ε is less than 0.2%.

2. The single crystal positive electrode material according to claim 1, characterized in that: The single crystal positive electrode material includes SO4 2- , the SO4 2- The content of is δ, wherein 0ppm≤δ≤800ppm.

3. The single crystal positive electrode material according to claim 1, characterized in that: The single crystal positive electrode material contains at least one single crystal grain with the same orientation, wherein the average grain size of the single crystal grain is 1 μm to 5 μm.

4. The single crystal positive electrode material according to claim 1, characterized in that: The extreme difference of the mass content of each element Ni, Co and Mn in the single crystal positive electrode material is ≤0.

08.

5. The single crystal positive electrode material according to claim 1, characterized in that: The single crystal positive electrode material also includes a coating layer, which includes a metal oxide or a lithium ion conductor, wherein the metal in the metal oxide includes at least one of Al, Ti, Zr, Y, Nb, Mg, W, B, Ce, Co and Mn.

6. The single crystal positive electrode material according to any one of claims 1 to 5, characterized in that: The single crystal positive electrode material satisfies at least one of the following characteristics: (1) The grain size of the single crystal positive electrode material is D, 150nm<D<250nm; (2) The average particle size D of the single crystal positive electrode material 50 1.5μm~5μm; (3) The tap density of the single crystal positive electrode material is greater than 1.5 g / cm 3 .

7. The single crystal positive electrode material according to claim 6, characterized in that: The single crystal positive electrode material satisfies at least one of the following characteristics: (1) The average particle size D of the single crystal positive electrode material 50 3.0~4.5μm; (2) The compaction density of the single crystal positive electrode material is 1.68 to 2.2 g / cm 3 ; (3) The chemical formula of the single crystal positive electrode material includes LiNi 0.67 Co 0.05 Mn 0.28 O2、LiNi 0.88 Co 0.06 Mn 0.04 O2 or LiNi 0.88 Co 0.06 Mn 0.03 Al 0.03 At least one of O2.

8. A cathode material precursor, characterized in that: The chemical formula of the positive electrode material precursor is Ni a Co b Mn c N d O e , wherein 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, 1≤e≤1.15, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; The surface area weighted average particle size D[3, 2] of the positive electrode material precursor is less than 2.0 μm, and the standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor is less than or equal to 0.

05.

9. The cathode material precursor according to claim 8, characterized in that: The positive electrode material precursor includes SO4 2- , the SO4 2- The content is η, wherein 0ppm≤η≤1800ppm.

10. The cathode material precursor according to claim 8, characterized in that: The extreme difference of the mass content of each element Ni, Co and Mn in the positive electrode material precursor is ≤0.

12.

11. The cathode material precursor according to claim 8, characterized in that: The positive electrode material precursor meets at least one of the following technical features: (1) The positive electrode material precursor includes secondary particles, and the secondary particles include a plurality of agglomerated primary particles; (2) The positive electrode material precursor includes secondary particles, the secondary particles include a plurality of agglomerated primary particles, and the primary particles are spherical; (3) The positive electrode material precursor includes secondary particles, the secondary particles include a plurality of agglomerated primary particles, and the particle size of the primary particles is 20 nm to 1000 nm.

12. The cathode material precursor according to claim 8, characterized in that: The positive electrode material precursor meets at least one of the following technical features: (1) The average particle size D of the positive electrode material precursor 50 <3.5μm; (2) The specific surface area of ​​the positive electrode material precursor is greater than 5 m 2 / g; (3) The tap density of the positive electrode material precursor is greater than 1 g / cm 3 .

13. A method for preparing a single crystal positive electrode material, characterized in that: The following steps are involved: A mixed solution containing nickel salt, cobalt salt and manganese salt is atomized and then thermally decomposed to obtain a positive electrode material precursor, wherein the surface area weighted average particle size D[3,2] of the positive electrode material precursor is less than 2.0 μm, and the standard deviation of the mass content of each element Ni, Co and Mn in the positive electrode material precursor is ≤0.05; The positive electrode material precursor is mixed with a lithium source and sintered in an oxygen-containing atmosphere to obtain a single crystal positive electrode material, wherein the standard deviation of the mass content of each element Ni, Co and Mn in the single crystal positive electrode material is ≤0.03; and the lattice strain of the single crystal positive electrode material is ε, and ε<0.2%.

14. The preparation method according to claim 13, characterized in that: The preparation method includes at least one of the following features: (1) The molar ratio of Ni, Co and Mn in the mixed solution is (50-98): (0-20): (0-30), and the content of Co and Mn in the mixed solution is not 0; (2) The total metal concentration in the mixed solution is 200 g / L to 500 g / L; (3) The mixed solution further includes a dopant containing an N element, wherein N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; (4) The chemical formula of the positive electrode material precursor is Ni a Co b Mn c N d O e , wherein 0.50≤a≤0.98, 0<b≤0.20, 0<c≤0.30, 0≤d≤0.10, a+b+c+d=1, 1≤e≤1.15, and N includes at least one of Al, Ti, Zr, Mg, Sr, Ba, Ca, Nb, W, Sb, Ta, Sn and Y; (5) The flow rate of the mixed solution is 100 L / h to 900 L / h; (6) The pressure of the atomization treatment is 0.4 MPa to 0.8 MPa; (7) The temperature of the thermal decomposition is 500°C to 850°C.

15. A lithium ion battery, characterized in that: The lithium-ion battery comprises the single crystal positive electrode material according to any one of claims 1 to 12 or the single crystal positive electrode material prepared by the method for preparing the single crystal positive electrode material according to any one of claims 13 or 14.

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