Cathode Material and Lithium-Ion Battery

Abstract

The present application discloses a cathode material, which is a lithium nickel cobalt-based composite oxide. The cathode material includes secondary particles, and the secondary particles include a plurality of primary particles. The cathode material has a primary particle microcrystalline coefficient P, and the microcrystalline coefficient P satisfies 20000 ≤ P ≤ 100000. By the above method, the present application provides a single crystal material, in which the number of microcrystals in the primary particles is increased, thereby enhancing the ionic conductivity of the material and overcoming the problems of large particle single crystal impedance and low capacity.

Description

Technical Field

[0001] The present application relates to the field of cathode materials; more specifically, the present application relates to a cathode material and a lithium-ion battery. Background Art

[0002] In recent years, the large-scale deployment of electric vehicles and energy storage systems has led to a sharp increase in the global demand for lithium-ion batteries, precisely because lithium-ion batteries have high energy density and power density. In the prior art, compared with polycrystalline materials, single-crystal materials have a longer lithium-ion transmission path, and their discharge specific capacity and rate performance are worse than those of polycrystalline materials. Specifically, the main problem in single-crystal cathode materials is the size problem. A large primary particle size will lead to a longer lithium-ion transmission path, a larger impedance, and a capacity decrease; a small primary particle size and insufficient growth will cause the adhesion between primary particles to be inseparable and become pseudo-polycrystalline, and the pseudo-polycrystalline material has low strength. The pseudo-polycrystalline may gradually crack during cycling, generating new surfaces that will cause side reactions in the material, thereby affecting the long-term performance of the lithium-ion battery. Summary of the Invention

[0003] In order to solve at least one or more of the above-mentioned technical problems, the present application proposes improvement solutions to the prior art in multiple aspects.

[0004] In a first aspect, the present application provides a cathode material, which is a lithium nickel cobalt composite oxide, and the cathode material includes a plurality of grains, and the grains include primary particles;

[0005] The cathode material has a primary particle microcrystalline coefficient P, , and the microcrystalline coefficient P satisfies 20000 ≤ P ≤ 100000;

[0006] wherein, d 104 is the atomic parallel spacing of the 104 crystal plane, that is, the microcrystalline size; D is the length of the average longest axis of the primary particle.

[0007] In a second aspect, the present application provides a lithium-ion battery, which includes the cathode material described in the first aspect.

[0008] The lithium-ion battery provided in the second aspect of the present application has the advantages of high discharge specific capacity, good rate performance, and high ionic conductivity.

[0009] The present application provides a cathode material. By limiting the P value of the crystallite coefficient of the primary particles within the range of 20,000 ≤ P ≤ 100,000, there are more crystallites in the primary particles, and there are certain gaps between the crystallites that can provide transmission channels for lithium ions, thereby increasing the lithium ion transmission channels within the primary particles. Therefore, the DCR (Direct Current Resistance) can be reduced and the capacity of the battery can be improved. Moreover, by increasing the number of crystallites in the primary particles, the problem of insufficient growth of the primary particles in traditional single crystal particles is solved; while the material grows into large particle single crystals, the number of crystallites in the particles is increased to enhance the ionic conductivity of the material, which not only solves the problem of the growth of large particle single crystals, but also solves the problem of high impedance and low capacity of large particle single crystals. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] By reading the following detailed description with reference to the accompanying drawings, the above and other objects, features and advantages of the exemplary embodiments of the present application will become readily understood. In the drawings, several embodiments of the present application are shown in an exemplary rather than restrictive manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:

[0011] Figure 1 Shows the scanning electron microscope photograph of Example 1;

[0012] Figure 2 Shows the scanning electron microscope photograph of Example 2;

[0013] Figure 3 Shows the scanning electron microscope photograph of Example 3;

[0014] Figure 4 Shows the scanning electron microscope photograph of Example 4;

[0015] Figure 5 Shows a schematic diagram of a battery in a discharged state, that is, during operation;

[0016] Figure 6 Shows the scanning electron microscope photograph of Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0018] It should be understood that the terms "comprising" and "including" as used in the specification and claims of this application indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their combinations.

[0019] It should also be understood that the terms used in the specification of this application are merely for the purpose of describing specific embodiments and are not intended to limit this application. As used in the specification and claims of this application, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include the plural forms. It should be further understood that the term "and / or" as used in the specification and claims of this application refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0020] As used in this specification and the claims, the term "if" can be interpreted as "when...", "once", "in response to determining", or "in response to detecting" depending on the context. Similarly, the phrase "if determined" or "if [the described condition or event] is detected" can be interpreted as meaning "once determined", "in response to determining", "once [the described condition or event] is detected", or "in response to detecting [the described condition or event]" depending on the context.

[0021] The specific embodiments of this application will be described in detail below with reference to the accompanying drawings. Unless otherwise specified, the materials, reagents and equipment used in the embodiments of this application are all obtained through conventional commercial channels.

[0022] Aiming at the deficiencies of the prior art, the purpose of this application is to provide a positive electrode material, the positive electrode material is a lithium nickel cobalt composite oxide, the positive electrode material includes a plurality of crystal grains, and the crystal grains include primary particles, wherein,

[0023] The positive electrode material has a primary particle microcrystalline coefficient P, , and the microcrystalline coefficient P satisfies 20000 ≤ P ≤ 100000; wherein,

[0024] d 104 is the atomic parallel spacing of the 104 crystal plane, that is, the microcrystalline size;

[0025] D is the length of the average longest axis of the primary particle.

[0026] It should be noted that the primary particle includes a plurality of microcrystals. In the primary particle microcrystalline coefficient, D refers to the length of the average longest axis of the primary particle, D 3 is the size of the primary particle, d 104 is the size of the microcrystal. Through It can be used to characterize the number of microcrystals present in the primary particles. Among them, the length of the average longest axis of the primary particles can be obtained by measuring the longest length of the primary particles through SEM (Scanning Electron Microscope); d 104 The full width at half maximum (FWHM) of the 104 crystal plane can be analyzed and obtained through XRD (X-ray Diffraction) analysis method, and then the full width at half maximum of the 104 crystal plane can be converted into the atomic parallel spacing through the Scherrer formula, so as to obtain d 104 . Specifically, , d 104 is the atomic parallel spacing (i.e., the microcrystal size) of the 104 crystal plane; k is a constant; λ is the X-ray wavelength; β is the full width at half maximum (FWHM) of the diffraction peak; θ is the diffraction angle.

[0027] Thus, by limiting the P value within the range of 20000 ≤ P ≤ 100000, a certain number of microcrystals exist in the primary particles, and there are certain gaps between the microcrystals, which can provide a transmission channel for lithium ions, so that the lithium ion transmission channels in the primary particles can be increased. Therefore, the DCR (Direct Current Resistance) can be reduced and the capacity of the cathode material can be improved. When P< 20000, the number of microcrystals in the primary particles is insufficient, resulting in insufficient lithium ion transmission channels, and the effect of reducing the direct current resistance and increasing the capacity cannot be achieved; when P >100000, the number of microcrystals in the primary particles is excessive, which may lead to a decrease in the structural strength of the primary particles, thereby affecting the cycle stability of the cathode material.

[0028] As an embodiment of the present invention, the cathode material satisfies the following conditions:

[0029] In the XRD pattern of the positive electrode material, there is a first peak between 2θ of 17° - 20°, and the first peak is the 003 peak. The full width at half maximum (FWHM) of the first peak is 0.08 - 0.20; the FWHM of the first peak can be 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.18, 0.20 or any value within the range formed by any two of the above values, which is not limited here. There is a second peak between 2θ of 42° - 45°, and the second peak is the 104 peak. The FWHM of the second peak is 0.10 - 0.30; the FWHM of the second peak can be 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.22, 0.24, 0.26, 0.28 or any value within the range formed by any two of the above values, which is not limited here. Thus, by limiting the FWHM of the first peak and the second peak within the above range, the grains of the positive electrode material have good microstrain while having a relatively large grain size, thereby increasing the structural stability of the grains and improving the cycle stability of the positive electrode material.

[0030] As an embodiment of the present invention, the positive electrode material has an atomic parallel spacing d of the 003 crystal plane 003 and an atomic parallel spacing d of the 104 crystal plane 104 .

[0031] Among them, the value range of d 003 is 80 - 160 nm, and the d 003 can be 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160 or any value within the range formed by any two of the above values, which is not limited here. When d 003 is within the above range, it indicates that the atomic parallel spacing on the 003 crystal plane is long enough, and the material forms a good layered structure microscopically, thereby facilitating the insertion and extraction of Li ions, reducing the DCR (Direct Current Resistance), and improving the capacity of the positive electrode material.

[0032] Among them, the value range of d 104 is 20 - 100 nm; the d 104 can be 20, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100 or any value within the range formed by any two of the above values, which is not limited here. By restricting d 104The value of satisfies 20 - 100 nm, such that the microcrystalline size within the primary particles can provide a certain structural strength, improving the cycle stability of the cathode material.

[0033] As an embodiment of the present invention, the primary particles of the cathode material have a length value D of the average longest axis, where D > 2.0 μm; D can be 2.05 μm, 2.10 μm, 2.15 μm, 2.20 μm, 2.25 μm, 2.30 μm, 2.35 μm, 2.40 μm, 2.45 μm, 2.50 μm, 2.55 μm, 2.60 μm, 2.70 μm, 2.80 μm or any value within the range formed by any two of the above values, which is not limited herein.

[0034] Among them, the average longest axis D is the average value of the longest diameters of the primary particles in the 3K multiples on the SEM of the cathode material. The primary particles having a relatively long average longest axis within the above range indicate that the primary particles grow larger and more uniformly, and at the same time, the primary particles have good structural strength.

[0035] As an embodiment of the present invention, the cathode material contains single crystals with the same orientation, where the length of the longest axis of the single crystal is 1 μm to 5 μm. Specifically, the length of the longest axis of the single crystal is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or any value within the range formed by any two of the above values, which is not limited herein. The primary particles of the cathode material have the same orientation, and the length of the longest axis of the primary particles is 1 μm - 5 μm. Specifically, the length of the longest axis of the primary particles is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or any value within the range formed by any two of the above values, which is not limited herein. The cathode material particles of the present application have single crystals with the same orientation. Since single crystals have a more stable structure, a more uniform bulk phase composition distribution, and better particle strength than polycrystals, the material can significantly reduce the cracking of the particles during the pressing process of the electrode sheet, improving the compaction density and volumetric energy density of the electrode sheet.

[0036] It should be noted that the difference between single-crystal cathode materials and polycrystalline cathode materials (i.e., polycrystalline secondary particles) is that the smallest particles of polycrystalline secondary particles are secondary particles formed by the aggregation of nanoscale primary particles. For single-crystal cathode materials, the smallest particles are usually micron-scale monomer primary particles. Generally speaking, in addition to EBSD testing methods, other characterization methods such as scanning electron microscopy (SEM) can also be used to determine whether the obtained cathode product is a single-crystal material. For example, for single-crystal cathode materials, the morphology of single-crystal particles can be characterized by SEM, and it can be seen that the shape of single-crystal particles generally shows regular or irregular spherical shapes, and there is no significant particle aggregation. The orientation of single-crystal cathode materials can also be characterized by EBSD. It can be observed by EBSD that the color within at least one grain is the same, so as to judge that the orientation within at least one grain is the same, and the grains with the same orientation are single crystals. It should be specifically noted that the "single-crystal cathode materials" well-known to those skilled in the art are not "single crystals" in the strict crystallographic sense. Crystallographically, an ideal single crystal refers to a crystal with exactly the same arrangement and direction. However, limited by impurities, strain, and crystal defects, ideal single crystals are very rare and difficult to produce in the laboratory. Therefore, the single-crystal cathode materials well-known in the art are actually more "single-crystal-like morphology" cathode materials, which only show a large particle size similar to that of single crystals in terms of size, different from polycrystals composed of many small primary particles.

[0037] As an embodiment of the present invention, the chemical general formula of the cathode material matrix is Li a Ni x M y N z X 1-x-y-z O 2b , where 0.98 ≤ a ≤ 1.05, 0.60 ≤ x < 1, 0 < y ≤ 0.40, 0 < z ≤ 0.003, 0.95 ≤ b ≤ 1.05, M is selected from at least one of Co, Mn, and Al, N is selected from at least one of Ti, Zr, Mg, Sr, Ba, Nb, W, and Y, and X is selected from one or more of W, Y, Mn, Os, Sb, V, and Cr. Preferably, 1.00 ≤ a ≤ 1.03, 0.60 ≤ x < 0.9, 0.1 < y ≤ 0.40, 0 < z ≤ 0.002, 1.00 ≤ b ≤ 1.03.

[0038] In the above chemical general formula, a can be 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05, or any value within the range formed by any two of the above values, and no further limitation is made here.

[0039] In the above chemical general formula, b can be 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05 or any value within the range formed by any two of the above values, and no limitation is made here.

[0040] In the above chemical general formula, x can be 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95 or any value within the range formed by any two of the above values, and no limitation is made here.

[0041] In the above chemical general formula, y can be 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40 or any value within the range formed by any two of the above values, and no limitation is made here.

[0042] In the above chemical general formula, z can be 0.0005, 0.001, 0.0015, 0.0020, 0.0025, 0.0030 or any value within the range formed by any two of the above values, and no limitation is made here.

[0043] In the above chemical general formula, element X is a high-valence element with a valence of greater than or equal to 5. Element X is selected from one or more of W, Y, Mn, Os, Sb, V. The positive electrode material includes a plurality of grains, and each grain includes an internal region. The distance from any point in the internal region to the surface of the grain is greater than 500 nm, and at least part of element X is located in the internal region of the grain. The fact that element X is located in the internal region of the grain can be characterized by the cross-section of the grain by ESD, showing that element X is located in the internal region. Thus, by having a high-valence element X with a valence of greater than or equal to 5 in the internal region of the grain, the high-valence element X can change the energy band structure of the grain, reduce the activation energy of electron migration, thereby reducing the energy barrier for Li ion migration, and further reducing the DCR (Direct Current Resistance), and improving the capacity of the positive electrode material.

[0044] As an embodiment of the present invention, the powder resistivity of the positive electrode material ; the powder resistivity can be, 、 、 、 、 、 、 、 or any value within the range formed by any two of the above values, and no limitation is made here. Preferably, the powder resistivity ; more preferably, the powder resistivity By controlling the powder resistivity of the positive electrode material within the above range, the positive electrode material has excellent powder conductivity and low resistance, thereby reducing the DCR (Direct Current Resistance) and improving the capacity of the positive electrode material.

[0045] As an embodiment of the present invention, the tap density of the positive electrode material is ≥ 3.00 g / cc; the tap density can be 3.00 g / cc, 3.05 g / cc, 3.10 g / cc, 3.15 g / cc, 3.20 g / cc, 3.25 g / cc, 3.30 g / cc, 3.35 g / cc, 3.40 g / cc, 3.45 g / cc, 3.50 g / cc, 3.55 g / cc, 3.60 g / cc, 3.65 g / cc or any value within the range formed by any two of the above values, which is not limited herein. The tap density of the positive electrode material is one of the indicators to measure the energy density of the material. If the tap density of the positive electrode material is too large, the positive electrode sheet is too dense, which is not conducive to the infiltration of the electrolyte into the positive electrode sheet, resulting in hindered lithium ion insertion and a decrease in the rate performance of the battery. If the tap density of the positive electrode material is too low, the energy density of the material will decrease. Controlling the tap density of the positive electrode material within the above range is beneficial for the positive electrode material to have both high energy density and excellent rate performance.

[0046] As an embodiment of the present invention, the median particle size D50 of the volume distribution particle size of the positive electrode material satisfies: 3 μm < D50 < 5 μm, and the volume distribution particle size D50 can be: 3.1 µm, 3.3 µm, 3.4 µm, 3.6 µm, 3.8 µm, 4 µm, 4.2 µm, 4.5 µm, 4.8 µm, 4.9 µm. Preferably, the median particle size D50 of the volume distribution particle size of the positive electrode material satisfies: 3.5 μm < D50 < 4.5 μm. The median particle size D50 represents the particle size of the material corresponding to when the cumulative particle size distribution percentage reaches 50% by volume. When the D50 of the positive electrode material is small, the particle size is small, the tap density is low, and the specific surface area is large, which easily leads to serious side reactions between the particle surface and the electrolyte, reducing safety and cycle life; when the D50 of the positive electrode material is large, the particle size is large, the internal stress of the particles increases, and at the same time, the electrochemical polarization and concentration polarization of lithium ions inside and outside the particles are aggravated, resulting in a decrease in the capacity and rate performance of the positive electrode material. Controlling the D50 of the positive electrode material within the above range is beneficial for the positive electrode material to maintain better tap density, specific capacity and cycle life.

[0047] As an embodiment of the present invention, the width of the volume particle size distribution of the positive electrode material satisfies: 1.0 ≤ Span ≤ 1.8;

[0048] Wherein,

[0049] 。

[0050] The width of the characteristic particle size distribution is represented by the function ; the above formula represents a typical particle size distribution width function.

[0051] The value of the volume particle size distribution width of the positive electrode material can be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7 or 1.8. The larger the Span value, the wider the particle size distribution of the material. A wider particle size distribution is beneficial to improving the space utilization rate during material stacking. Small particles fill the gaps between large particles, and even smaller particles fill the smaller gaps; a high space utilization rate requires a sufficient combination of small and large particles, which also requires a wider particle size distribution. Therefore, as described above, the Span value represents the particle size distribution width. By controlling the Span value of the positive electrode material within the above range, it is beneficial to improve the powder compaction density of the material and reduce the powder resistance.

[0052] As an embodiment of the present invention, the ratio of the discharge capacity to the charge capacity of the positive electrode material at 0.1C ≥ 90.0%, and the ratio of the discharge capacity of the positive electrode material at 0.5C to the discharge capacity at 0.1C ≥ 96.5%. The ratio of the discharge capacity to the charge capacity of the positive electrode material at 0.1C can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97% or 98%. The ratio of the discharge capacity of the positive electrode material at 0.5C to the discharge capacity at 0.1C can be 96.5%, 96.6%, 96.7%, 96.8%, 96.9%, 97%, 97.4% or 97.5%. Controlling the specific capacity within the above range is beneficial for the positive electrode material to maintain better energy density and cycle life.

[0053] This application also relates to a preparation method of a high-capacity positive electrode material, and this preparation method has the following steps:

[0054] Step S1, preparing a solution by mixing metal salts of Ni, Co, and Mn in a certain proportion; adjusting the concentration of the solution; spraying the solution into a pyrolysis tower for reaction to finally obtain an oxide precursor.

[0055] Among them, the precursor is prepared by the above preparation method, which has a short reaction time, less pollution, and low cost. Moreover, at least part of the precursor prepared by the above method has a spinel structure, and the precursor with a spinel structure is more likely to form a layered structure when forming the cathode material. Specifically, the precursor prepared by the above preparation method belongs to a two-phase mixture of spinel and rock salt phases, and its structure is closer to the layered phase than that of the co-precipitation precursor. Therefore, even if there is interference from high-valence transition metal elements during the reaction phase transition, it is easier to grow into a good layered structure, thereby providing better conditions for subsequent doping of high-valence elements. On the other hand, compared with the co-precipitation process commonly used in the prior art, the precursor material obtained by co-precipitation has low crystallinity, poor tolerance to doping of large-radius elements, and high-valence elements are likely to adhere to the material surface, thereby inhibiting crystal growth and dispersion, making it difficult to form good single-crystal particles. Moreover, the precursor prepared by the above preparation method is an oxide, and this oxide is formed in an environment with a temperature above 600 °C, with a high degree of oxidation. Part of the crystal lattice in the precursor forms a spinel phase and has a higher lattice order. The chemical reaction energy required to transform from the ordered spinel phase or rock salt phase to the layered phase is lower, and it is easier to form an ordered layered phase, which is beneficial to reducing the full width at half maximum of the 104 peak of the cathode material.

[0056] In some embodiments, metal salts of Ni, Co, and Mn are formulated into a solution in a certain proportion. For example, the solution can be at least one of a nitrate solution, a sulfate solution, a chloride solution, and an acetate solution; in the metal salt solutions of Ni, Co, and Mn, the molar ratio of Ni, Co, and Mn can be 3-9:1-4:1-4, and the sum of the molar ratios of Ni, Co, and Mn is 1. For example, the above molar ratio can be any value among 6:1:3, 8:1:1, or 5:2:3.

[0057] In some embodiments, the precursor obtained in the above step S1 is an oxide; the general formula of the precursor is Ni x M y N 1-x-y O b , where 0.60 ≤ x < 1, 0 < y ≤ 0.40, 0.95 ≤ b ≤ 1.05. Preferably, 0.60 ≤ x < 0.9, 0 < y ≤ 0.30, 0.98 ≤ b ≤ 1.05.

[0058] In some embodiments, the concentration range of the solution is 0.05 mol / L - 2 mol / L. For example, the concentration value of the solution can be 0.05 mol / L, 0.07 mol / L, 0.08 mol / L, 0.14 mol / L, 0.36 mol / L, 0.66 mol / L, 0.89 mol / L, 1.13 mol / L, 1.45 mol / L, 1.68 mol / L, 2 mol / L or any value within the range formed by any two of the above values.

[0059] In some embodiments, the solution is sprayed into the pyrolysis tower, wherein the nozzle pressure is 1 - 5 Mpa. The nozzle pressure can be 1 Mpa, 1.5 Mpa, 2 Mpa, 2.5 Mpa, 3 Mpa, 3.5 Mpa, 4 Mpa, 4.5 Mpa, 5 Mpa or any value within the range formed by any two of the above values, which is not limited herein. Preferably, the nozzle pressure is 3.3 - 5 MPa.

[0060] The temperature in the pyrolysis tower is 600 - 1050 °C. The temperature can be 600 °C, 650 °C, 700 °C, 750 °C, 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C or any value within the range formed by any two of the above values, which is not limited herein.

[0061] Step S2: Mix the precursor, lithium source, and dopant prepared by spray pyrolysis, and then perform the first heat treatment to obtain a pre - sintered product; then add the lithium source and mix it with the pre - sintered product for the second heat treatment to obtain a sintered product.

[0062] Among them, by controlling the content of lithium during the first heat treatment, the positions occupied by Li ions in the bulk phase are reduced, facilitating the entry of the high - valence element X into the bulk phase, thereby improving the doping effect of the high - valence element X; moreover, during the first heat treatment, the heat treatment temperature is relatively low, which can promote the doping of the high - valence element X into the bulk phase. After the high - valence element X enters the bulk phase, it can increase the nucleation energy barrier and reduce the nucleation density. A lower nucleation density means that there is more raw material available for growth around each nucleus, which is conducive to the growth of primary particles. The relatively low temperature of the first heat treatment promotes the growth of microcrystals in the primary particles, increases the full width at half maximum of the 104 crystal plane, reduces the atomic parallel spacing of the 104 crystal plane, and makes the number of microcrystals within a suitable range. During the second heat treatment, by continuously increasing the lithium source and with a relatively high temperature of the second heat treatment, it promotes the growth within the primary particles and controls the length of the major axis of the primary particles to be within a suitable range.

[0063] In some embodiments, the dopant further includes element X, the valence state of element X is ≥5, and element X is selected from one or more of W, Y, Mn, Os, Sb, and V. Thus, by having the valence state of element X in the dopant greater than 5, the high-valence dopant element X can promote the growth of primary particles to control the length of the average longest axis of the primary particles.

[0064] In some embodiments, the dopant containing element X can be an oxide, hydroxide, or hydroxy-oxide. For example, the dopant containing element X can be WO3, Y2O5, OsO4, V2O5, Sb2O5, CrO3, Mn2O7.

[0065] In some embodiments, the dopant can further include an oxide, hydroxide, or hydroxy-oxide of element N; element N is selected from at least one of Ti, Zr, Mg, Sr, Ba, Nb, W, and Y.

[0066] In some embodiments, the specific form of the lithium source can be lithium carbonate, lithium hydroxide, lithium nitrate, or lithium chloride.

[0067] In some embodiments, the molar ratio of the precursor to the total amount of lithium source added can be 1:0.98 - 1.1. For example, the molar ratio of the precursor to the total amount of lithium source added can be 1:0.98, 1:0.99, 1:1.02, 1:1.05, 1:1.10, or any value within the range formed by any two of the above values, which is not limited herein.

[0068] In some embodiments, the lithium source added in the first heat treatment accounts for 30 - 90% of the total amount of lithium source added. For example, the lithium source added before the first heat treatment accounts for 30%, 35%, 40%, 45%, 50%, 60%, 70%, 80%, 90% of the total amount of lithium source added, or any value within the range formed by any two of the above values, which is not limited herein. Preferably 40 - 80%, more preferably 50 - 65%. Thus, by controlling the appropriate amount of lithium source added in the first heat treatment, the positions occupied by Li ions in the bulk phase can be reduced, facilitating the entry of the high-valence element X into the bulk phase, improving the doping effect of the high-valence element X, being conducive to the growth of primary particles, and making the length of the longest axis of the primary particles within a suitable range.

[0069] In some embodiments, the lithium source added in the second heat treatment accounts for 10 - 70% of the total amount of lithium source added. For example, the lithium source added before the second heat treatment accounts for 10%, 20%, 30%, 40%, 45%, 50%, 60%, 70% of the total amount of lithium source added, or any value within the range formed by any two of the above values. Preferably 20 - 60%, more preferably 35 - 50%.

[0070] In some embodiments, the first heat treatment is preferably carried out in an air atmosphere, and the temperature range of the first heat treatment is 600 °C to 1000 °C. Controlling the temperature of the first heat treatment within the above range is beneficial for the doping of the high-valence element X into the bulk phase and the growth of the primary particles, promoting the premature physical and chemical nucleation of the cathode material, so that the length of the longest axis in the primary particles is within a suitable range. The temperature of the first heat treatment can be any value within the range formed by any two of 600 °C, 620 °C, 650 °C, 680 °C, 700 °C, 720 °C, 750 °C, 780 °C, 800 °C, 820 °C, 850 °C, 880 °C, 900 °C, 920 °C, 950 °C, 980 °C, 1000 °C, which is not limited here. Preferably, the temperature of the first heat treatment is 780 °C to 980 °C, and more preferably 850 °C to 950 °C.

[0071] In some embodiments, the time of the first heat treatment is 1 h - 8 h. Controlling the temperature of the first heat treatment within the above range is beneficial for promoting the doping of the high-valence element X into the bulk phase, thus facilitating the growth of the primary particles and controlling the length of the longest axis of the primary particles within a suitable range. The time of the first heat treatment can be any value within the range formed by any two of 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, which is not limited here. Preferably, the time of the first heat treatment is 2 h - 6 h, and more preferably, the time of the first heat treatment is 3.5 h - 4 h.

[0072] In some embodiments, the second heat treatment is preferably carried out in an oxygen atmosphere, and the temperature range of the second heat treatment is 800 °C to 1100 °C. Controlling the temperature of the second heat treatment within the above range can control the number of microcrystals of the primary particles, so that the length of the longest axis of the primary particles is within a suitable range. The temperature of the second heat treatment can be any value within the range formed by any two of 800 °C, 820 °C, 850 °C, 880 °C, 900 °C, 920 °C, 950 °C, 980 °C, 1000 °C, 1020 °C, 1050 °C, 1080 °C, 1100 °C, which is not limited here. Preferably, the temperature of the second heat treatment is 910 °C to 1030 °C, and more preferably, the temperature of the second heat treatment is 930 °C to 970 °C.

[0073] In some embodiments, the time of the second heat treatment is 6 h - 16 h. The time of the second heat treatment can be any value within the range formed by any two of the following values: 6 h, 6.5 h, 7 h, 7.5 h, 8 h, 8.5 h, 9 h, 9.5 h, 10 h, 10.5 h, 11 h, 11.5 h, 12 h, 13 h, 14 h, 15 h, 16 h, which is not limited herein. Preferably, the time of the second heat treatment is 7 h - 12 h, and more preferably, the time of the second heat treatment is 7.5 h - 8.5 h.

[0074] Step S3: After crushing the first sintered product, mix it with the coating and sinter to obtain the positive electrode material.

[0075] In some embodiments, the coating contains at least one of the following elements: B, Ti, W, Al, Mg.

[0076] In some embodiments, the coating includes at least one of WO3, TiO2, and Al(OH)3. For example, the coating can be WO3, TiO2, Al(OH)3, a mixture of WO3 and TiO2, or a mixture of WO3 and Al(OH)3.

[0077] In some embodiments, based on the first sintered product, the mass fraction of the coating is 0.05 - 0.45 wt.%. For example, the mass fraction of the coating is 0.05 wt.%, 0.08 wt.%, 0.10 wt.%, 0.20 wt.%, 0.25 wt.%, 0.32 wt.%, 0.40 wt.%, 0.45 wt.%. Preferably, based on the first sintered product, the mass fraction of the coating is 0.20 - 0.35 wt.%.

[0078] In some embodiments, the temperature range of the secondary sintering is 400°C - 550°C. The temperature of the secondary sintering can be any value within the range formed by any two of the following values: 400°C, 420°C, 440°C, 460°C, 480°C, 500°C, 520°C, 540°C, 550°C, which is not limited herein. Preferably, the temperature range of the secondary sintering is 420°C - 480°C.

[0079] One embodiment of the present application provides a secondary battery (such as a lithium-ion battery, a sodium-ion battery, etc.), including a housing, an electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are both located inside the housing.

[0080] The housing can be a packaging bag encapsulated with a packaging film (such as an aluminum-plastic film). For example, the secondary battery is a soft-pack battery. In some other embodiments, the secondary battery can also be a steel-shell battery, an aluminum-shell battery, etc.

[0081] Figure 5 Shows a schematic diagram of a battery in a discharged state, i.e., during operation. As Figure 5 shown, the electrode assembly includes a positive electrode sheet 110, a negative electrode sheet 120, and a separator 130. The separator is disposed between the positive electrode sheet and the negative electrode sheet. The electrode assembly may be a stacked structure, which is formed by alternately laminating the positive electrode sheet, the separator, and the negative electrode sheet in sequence. In some other embodiments, the electrode assembly may also be a wound structure, which is formed by laminating the positive electrode sheet, the separator, and the negative electrode sheet in sequence and then winding them.

[0082] Positive electrode sheet

[0083] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer disposed on at least one surface of the positive electrode current collector. The positive electrode current collector may use aluminum foil, nickel foil, etc., or may also be a composite current collector disclosed in any prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive electrode active layer contains a positive electrode active material, and the positive electrode active material includes a compound that reversibly intercalates and deintercalates metal ions.

[0084] Negative electrode sheet

[0085] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector may use at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or a carbon-based current collector, etc., or may also be a composite current collector disclosed in any prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and a polymer substrate. The negative electrode active material layer includes a negative electrode material.

[0086] During the operation of the battery, i.e., when the battery is in a discharged state, metal ions (such as lithium ions) in the negative electrode escape from the lattice of the negative electrode material, pass through the electrolyte / electrolyte across the separator, and intercalate into the lattice of the positive electrode material.

[0087] Conversely, when the battery is charged by applying an external circuit, the oxidation of the positive electrode material causes metal ions (such as lithium ions) in the positive electrode to escape from the lattice of the positive electrode material, pass through the electrolyte / electrolyte across the separator, and move to the negative electrode; at the same time, the negative electrode material undergoes a reduction reaction, resulting in the intercalation of metal ions into the lattice of the negative electrode material.

[0088] With the reciprocation of metal ions between the positive electrode and the negative electrode, the battery can achieve the discharge and charge processes in thousands of cycles.

[0089] Specific embodiments and comparative examples

[0090] Example 1

[0091] 1. Prepare a nitrate solution by mixing nitrates of Ni, Co, and Mn in a molar ratio of 6:1:3; adjust the concentration of the nitrate solution to 0.1 mol / L; spray the nitrate solution into a pyrolysis tower for reaction, set the nozzle pressure to 3.3 Mpa, and the temperature in the pyrolysis tower to 900 °C to obtain an oxide precursor Ni 0.6 Co 0.1 Mn 0.3 O.

[0092] 2. Mix the oxide precursor, lithium carbonate, and WO3 and conduct the first heat treatment. During the first heat treatment, the molar ratio of lithium carbonate to the precursor is 0.60:1, the mass content of WO3 is 0.10 wt.% of the mass of the precursor, the temperature of the first heat treatment is 780 °C, and the treatment time is 4 h. After cooling, a pre-sintered product is obtained. Continue to add lithium carbonate and mix it with the pre-sintered product for the second heat treatment. During the second heat treatment, the molar ratio of the added lithium carbonate to the precursor is 0.43:1, the sintering temperature of the second heat treatment is 900 °C, and the heat treatment time is 8 h to obtain a first sintered product.

[0093] 3. After pulverizing the first sintered product with a jet mill, mix it with WO3 and TiO2 and sinter to obtain the positive electrode material. Among them, the mass content of WO3 is 0.15 wt.% of the first sintered product, the mass content of TiO2 is 0.10 wt.% of the first sintered product, and the sintering temperature is 420 °C. The chemical formula of the positive electrode material is: LiNi 0.6 Co 0.1 Mn 0.3 O2.

[0094] Example 2

[0095] 1. Prepare a nitrate solution by mixing nitrates of Ni, Co, and Mn in a molar ratio of 6:1:3; adjust the concentration of the solution to 0.15 mol / L; spray the solution into a pyrolysis tower for reaction, set the nozzle pressure to 5 Mpa, and the temperature in the pyrolysis tower to 950 °C to obtain an oxide precursor Ni 0.6 Co 0.1 Mn 0.3 O.

[0096] 2. Mix the oxide precursor with lithium carbonate, WO3, and ZrO2 and then conduct the first heat treatment. Among them, the molar ratio of lithium carbonate added in the first heat treatment to the precursor is 0.6:1, the mass content of WO3 is 0.12 wt.% of the mass of the precursor, and the mass content of ZrO2 is 0.22 wt.% of the mass of the precursor. The temperature of the first heat treatment is 780 °C, and the treatment time is 4 h. After cooling, a pre-sintered product is obtained. Continue to add lithium carbonate and mix it with the pre-sintered product for the second heat treatment. Among them, the molar ratio of lithium carbonate added in the second heat treatment to the precursor is 0.43:1, the sintering temperature of the second heat treatment is 900 °C, and the heat treatment time is 8 h to obtain the first sintered product.

[0097] 3. Crush the first sintered product and then mix and sinter it with WO3, Al(OH)3, and TiO2 to obtain the positive electrode material. Among them, the mass content of WO3 is 0.15 wt.% of the first sintered product, the mass content of TiO2 is 0.05 wt.% of the first sintered product, and the mass content of Al(OH)3 is 0.05 wt.% of the first sintered product. The sintering temperature is 440 °C. The chemical formula of the positive electrode material is: LiNi 0.6 Co 0.1 Mn 0.3 O2.

[0098] Example 3

[0099] 1. Prepare a sulfate solution of Ni, Co, and Mn according to a molar ratio of 6:1:3; adjust the concentration of the solution to 0.1 mol / L; spray the solution into the pyrolysis tower for reaction, set the nozzle pressure to 3.5 Mpa, and the temperature in the pyrolysis tower to 950 °C to obtain the oxide precursor Ni 0.6 Co 0.1 Mn 0.3 O.

[0100] 2. Mix the obtained oxide precursor with lithium nitrate, WO3, and ZrO2 and then conduct the first heat treatment. Among them, during the first heat treatment, the molar ratio of lithium nitrate to the precursor is 0.6:1, the mass content of WO3 is 0.15 wt.% of the mass of the precursor, and the mass content of ZrO2 is 0.22 wt.% of the mass of the precursor. The temperature of the first heat treatment is 780 °C, and the treatment time is 4 h. After cooling, a pre-sintered product is obtained. Continue to add lithium nitrate and mix it with the pre-sintered product for the second heat treatment. Among them, the molar ratio of lithium nitrate added in the second heat treatment to the precursor is 0.43:1, the sintering temperature of the second heat treatment is 900 °C, and the heat treatment time is 8 h to obtain the first sintered product.

[0101] 3. After crushing the first sintered product, it is mixed and sintered with WO3, Al(OH)3 and TiO2 to obtain the positive electrode material. Among them, the mass content of WO3 is 0.15 wt.% of the first sintered product, the mass content of TiO2 is 0.05 wt.% of the first sintered product, the mass content of Al(OH)3 is 0.05 wt.% of the first sintered product, and the sintering temperature is 440 °C. The chemical formula of the positive electrode material is: LiNi 0.6 Co 0.1 Mn 0.3 O2.

[0102] Example 4

[0103] 1. Prepare a sulfate solution of Ni, Co, and Mn in a molar ratio of 6:1:3; adjust the concentration of the sulfate solution to 0.1 mol / L; spray the sulfate solution into the pyrolysis tower for reaction, set the nozzle pressure to 5 Mpa, and the temperature in the pyrolysis tower to 900 °C to obtain the oxide precursor Ni 0.6 Co 0.1 Mn 0.3 O.

[0104] 2. Mix the oxide precursor with lithium nitrate, WO3 and ZrO2 and conduct the first heat treatment. Among them, during the first heat treatment, the molar ratio of lithium nitrate to the precursor is 0.6:1, the mass content of WO3 is 0.12 wt.% of the mass of the precursor, the mass content of ZrO2 is 0.22 wt.% of the mass of the precursor, the temperature of the first heat treatment is 780 °C, and the treatment time is 4 h. After cooling, a pre-sintered product is obtained. Continue to add lithium nitrate and mix it with the pre-sintered product for the second heat treatment. Among them, the molar ratio of lithium nitrate added in the second heat treatment to the precursor is 0.43:1, the sintering temperature of the second heat treatment is 900 °C, and the heat treatment time is 8 h to obtain the first sintered product.

[0105] 3. After crushing the first sintered product, it is mixed and sintered with WO3, Al(OH)3 and TiO2 to obtain the positive electrode material. Among them, the mass content of WO3 is 0.20 wt.% of the first sintered product, the mass content of TiO2 is 0.15 wt.% of the first sintered product, the mass content of Al(OH)3 is 0.05 wt.% of the first sintered product, and the sintering temperature is 440 °C. The chemical formula of the positive electrode material is: LiNi 0.6 Co 0.1 Mn 0.3 O2.

[0106] Example 5

[0107] 1. Prepare a sulfate solution by mixing sulfates of Ni, Co, and Mn in a molar ratio of 6:1:3; adjust the concentration of the sulfate solution to 0.1 mol / L; spray the solution into a pyrolysis tower for reaction, set the nozzle pressure at 3.5 Mpa, and the temperature in the pyrolysis tower at 900 °C to obtain an oxide precursor Ni 0.6 Co 0.1 Mn 0.3 O.

[0108] 2. Mix the oxide precursor with lithium carbonate, V2O5, and ZrO2 and conduct the first heat treatment. During the first heat treatment, the molar ratio of lithium carbonate to the precursor is 0.6:1, the mass content of V2O5 is 0.12 wt.% of the mass of the precursor, and the mass content of ZrO2 is 0.22 wt.% of the mass of the precursor. The temperature of the first heat treatment is 780 °C, and the treatment time is 4 h. After cooling, a pre-sintered product is obtained. Continue to add lithium carbonate and mix it with the pre-sintered product for the second heat treatment. During the second heat treatment, the molar ratio of lithium carbonate added to the precursor is 0.43:1, the sintering temperature of the second heat treatment is 900 °C, and the heat treatment time is 8 h to obtain a first sintered product.

[0109] 3. Crush the first sintered product and mix it with WO3, Al(OH)3, and TiO2 for sintering to obtain the positive electrode material. Among them, the mass content of WO3 is 0.15 wt.% of the first sintered product, the mass content of TiO2 is 0.05 wt.% of the first sintered product, the mass content of Al(OH)3 is 0.05 wt.% of the first sintered product, and the sintering temperature is 440 °C. The chemical formula of the positive electrode material is: LiNi 0.6 Co 0.1 Mn 0.3 O2.

[0110] Example 6

[0111] 1. Prepare a nitrate solution by mixing nitrates of Ni, Co, and Mn in a molar ratio of 6:1:3; adjust the concentration of the solution to 0.15 mol / L; spray the solution into a pyrolysis tower for reaction, set the nozzle pressure at 5 Mpa, and the temperature in the pyrolysis tower at 900 °C to obtain an oxide precursor Ni 0.6 Co 0.1 Mn 0.3 O.

[0112] 2. Mix the oxide precursor with lithium carbonate, Nb2O5, and ZrO2 and then conduct the first heat treatment. Among them, the molar ratio of lithium carbonate added in the first heat treatment to the precursor is 0.6:1, the mass content of Nb2O5 is 0.12 wt.% of the mass of the precursor, and the mass content of ZrO2 is 0.22 wt.% of the mass of the precursor. The temperature of the first heat treatment is 780 °C, and the treatment time is 4 h. After cooling, a pre-sintered product is obtained. Continue to add lithium carbonate and mix it with the pre-sintered product for the second heat treatment. Among them, the molar ratio of lithium carbonate added in the second heat treatment to the precursor is 0.43:1, the sintering temperature of the second heat treatment is 900 °C, and the heat treatment time is 8 h to obtain the first sintered product.

[0113] 3. Crush the first sintered product and then mix and sinter it with WO3, Al(OH)3, and TiO2 to obtain the positive electrode material. Among them, the mass content of WO3 is 0.15 wt.% of the first sintered product, the mass content of TiO2 is 0.05 wt.% of the first sintered product, the mass content of Al(OH)3 is 0.05 wt.% of the first sintered product, and the sintering temperature is 440 °C. The chemical formula of the positive electrode material is: LiNi 0.6 Co 0.1 Mn 0.3 O2.

[0114] Example 7

[0115] 1. Prepare a nitrate solution of Ni, Co, and Mn according to a molar ratio of 8:1:1; adjust the concentration of the solution to 0.1 mol / L; spray the solution into the pyrolysis tower for reaction, set the nozzle pressure to 3.5 Mpa, and the temperature in the pyrolysis tower to 950 °C to obtain the oxide precursor Ni 0.8 Co 0.1 Mn 0.1 O.

[0116] 2. Mix the oxide precursor with lithium nitrate, OsO4, and Y2O5 and then conduct the first heat treatment. During the first heat treatment, the molar ratio of lithium nitrate to the precursor is 0.6:1, the mass content of OsO4 is 0.05 wt.% of the mass of the precursor, the mass content of Y2O5 is 0.12 wt.% of the mass of the precursor, the temperature of the first heat treatment is 780 °C, and the treatment time is 4 h. After cooling, a pre-sintered product is obtained. Continue to add lithium nitrate and mix it with the pre-sintered product for the second heat treatment. Among them, the molar ratio of lithium nitrate added in the second heat treatment to the precursor is 0.43:1, the sintering temperature of the second heat treatment is 900 °C, and the heat treatment time is 8 h to obtain the first sintered product.

[0117] 3. The first sintered product is pulverized and then mixed and sintered with WO3, Al(OH)3 and TiO2 to obtain the positive electrode material. Among them, the mass content of WO3 is 0.15 wt.% of the first sintered product, the mass content of TiO2 is 0.05 wt.% of the first sintered product, the mass content of Al(OH)3 is 0.15 wt.% of the first sintered product, and the sintering temperature is 460 °C. The chemical formula of the positive electrode material is: LiNi 0.6 Co 0.1 Mn 0.3 O2.

[0118] Example 8

[0119] 1. Nitrates of Ni, Co, and Mn are prepared into a nitrate solution according to a molar ratio of 5:2:3; the concentration of the solution is adjusted to 0.1 mol / L; the solution is sprayed into a pyrolysis tower for reaction, the nozzle pressure is set to 3.3 Mpa, and the temperature in the pyrolysis tower is 900 °C to obtain an oxide precursor Ni 0.5 Co 0.2 Mn 0.3 O.

[0120] 2. The obtained oxide precursor is mixed with lithium carbonate, ZrO2 and Y2O5 and then subjected to the first heat treatment. Among them, during the first heat treatment, the molar ratio of lithium carbonate to the precursor is 0.6:1, the mass content of ZrO2 is 0.32 wt.% of the mass of the precursor, the mass content of Y2O5 is 0.12 wt.% of the mass of the precursor, the temperature of the first heat treatment is 780 °C, the treatment time is 4 h, and after cooling, a pre-sintered product is obtained. Lithium carbonate is continuously added and mixed with the pre-sintered product for the second heat treatment. Among them, the molar ratio of lithium carbonate added in the second heat treatment to the precursor is 0.43:1, the sintering temperature of the second heat treatment is 910 °C, and the heat treatment time is 8 h to obtain the first sintered product.

[0121] 3. The first sintered product is pulverized and then mixed and sintered with WO3, Al(OH)3 and TiO2 to obtain the positive electrode material. Among them, the mass content of WO3 is 0.15 wt.% of the first sintered product, the mass content of TiO2 is 0.05 wt.% of the first sintered product, the mass content of Al(OH)3 is 0.15 wt.% of the first sintered product, and the sintering temperature is 460 °C. The chemical formula of the positive electrode material is: LiNi 0.6 Co 0.1 Mn 0.3 O2.

[0122] Example 9

[0123] The difference between this example and Example 1 is that during the first heat treatment process, the molar ratio of lithium carbonate to the precursor is 0.30:1, the mass content of WO3 is 0.25 wt.% of the mass of the precursor, and the temperature of the first heat treatment is 700 °C.

[0124] Example 10

[0125] The difference between this example and Example 1 is that during the first heat treatment process, the molar ratio of lithium carbonate to the precursor is 0.20:1, the mass content of WO3 is 0.30 wt.% of the mass of the precursor, and the temperature of the first heat treatment is 600 °C.

[0126] Comparative Example 1

[0127] 1. Perform a primary sintering treatment on the mixture of the co-precipitated precursor Ni 0.6 Co 0.1 Mn 0.3 (OH)2, lithium carbonate with a molar ratio of 1.03:1 to the precursor, and 0.32 wt.% ZrO2 as a dopant at a sintering temperature of 900 °C to obtain a first sintered product; the weight percentages in Step 1 are based on the weight of the precursor.

[0128] 2. After pulverizing the first sintered product, sinter it together with 0.15 wt.% WO3, 0.05 wt.% TiO2, and 0.15 wt.% Al(OH)3 at 460 °C to obtain the final product; the weight percentages in Step 2 are all based on the weight of the first sintered product.

[0129] Comparative Example 2

[0130] 1. Perform a primary sintering treatment on the mixture of the co-precipitated precursor Ni 0.6 Co 0.1 Mn 0.3 (OH)2, lithium nitrate with a molar ratio of 1.03:1 to the precursor, and 0.22 wt.% ZrO2 and 0.12 wt.% WO3 as dopants at a sintering temperature of 900 °C to obtain a first sintered product; the weight percentages in Step 1 are all based on the weight of the precursor.

[0131] 2. After pulverizing the first sintered product, sinter it together with 0.15 wt.% WO3, 0.05 wt.% TiO2, and 0.15 wt.% Al(OH)3 at 460 °C to obtain the final product; the weight percentages in Step 2 are all based on the weight of the first sintered product.

[0132] Comparative Example 3

[0133] 1. Spray pyrolysis precursor Ni 0.6 Co 0.1 Mn0.3 A mixture of O, lithium nitrate with a molar ratio of 1.03:1 to the precursor, and dopants 0.32 wt.% ZrO2 and 0.15 wt.% MgO is subjected to a first sintering treatment at a sintering temperature of 900 °C to obtain a first sintered product; the weight percentages in step 1 are all based on the weight of the precursor.

[0134] 2. The first sintered product is pulverized and then sintered together with 0.15 wt.% WO3, 0.05 wt.% TiO2 and 0.15 wt.% Al(OH)3 at 460 °C to obtain the final product; the weight percentages in step 2 are all based on the weight of the first sintered product.

[0135] 2. The first sintered product is pulverized and then sintered together with 0.15 wt.% WO3, 0.05 wt.% TiO2 and 0.15 wt.% Al(OH)3 at 460 °C to obtain the final product; the weight percentages in step 2 are all based on the weight of the first sintered product.

[0136] Performance test:

[0137] Testing of the D50 and Span values of the cathode material:

[0138] The particle size distribution of the material is characterized using Mastersizers 3000

[0139] The characteristic particle size distribution width of the above material is represented by the function as:

[0140] ;

[0141] The above formula represents a typical particle size distribution width function. The larger the Span value, the wider the particle size distribution of the material.

[0142] is the particle size at which the number distribution frequency is less than or equal to the percentage n%:

[0143] .

[0144] Testing of the value D of the average longest axis of the primary particles

[0145] The morphology of the material is observed through Hitachi S4800 typeCharacterization by electron microscope. The Hitachi S4800 high-magnification electron microscope was used. The powder sample was directly tested without treatment. Photos were taken at a magnification of 3K. In the photos, the longest diameter of all particles was measured, and then the average value was statistically calculated to obtain the average longest axis D of the primary particles of the material. Specifically, the value of D was obtained by measuring the longest sides of all primary particles in the 3000-fold electron microscope image through the software "Nano Measurer 1.2" and then calculating the average value.

[0146] XRD test

[0147] The crystallographic structure of the material was characterized by X'Pert Powder (PANalytical), and the conditions were as follows: scanning range: 2θ = 10 - 90 °C, scanning time 4.8 min; the obtained (XRD) results were peak-searched and analyzed by professional software to obtain the full width at half maximum (FWHM) and peak positions of 003 and 104.

[0148] The full width at half maximum was converted into the atomic plane spacing through the Scherrer formula to obtain the values of d003 and d104. That is:

[0149]

[0150] where d x is the atomic plane spacing of a certain plane; is a constant; is the X-ray wavelength; is the full width at half maximum (FWHM) of the diffraction peak; is the diffraction angle. Then, the value of Dp was obtained by summing and averaging d003 and d104.

[0151] Tap density test

[0152] The test was carried out using a Quantachrome tap density tester (model: DAT-4-220) in the United States.

[0153] Compacted density test

[0154] The test was carried out using a Carver 4350 in the United States. The steps were as follows: Weigh 1 g of the sample and put it into the mold, apply a pressure of 3 T for 30 s, and then measure the height after pressing to calculate the compaction.

[0155] Powder resistivity test

[0156] The powder resistivity was measured by an ST2722-SZ powder resistivity tester. The steps were as follows:

[0157] 1. Take the powder sample and add it to the feeding chamber until it is full and slightly overflowing, and then slightly compact and flatten it with a small spoon;

[0158] 2. Turn the hand wheel counterclockwise to press down the upper electrode. Pressurize in stages until the pressure to be measured is reached, and read the pressure and resistivity of the pressed powder on the panel of the test instrument.

[0159] Electron Backscatter Diffraction (EBSD) Test:

[0160] The cathode material sample was first embedded in a carbon paint (PELCO) graphite block, and then the cross section of the block was polished with an argon ion beam. Electron backscatter diffraction (EBSD) imaging was performed using a JEOL JSM-7000F scanning electron microscope. The step size of the EBSD image was set to 250 nm (each pixel was 250 nm × 250 nm).

[0161] The positive electrode material containing single grains with the same orientation can be tested by electron backscatter diffraction (EBSD). By observing and measuring the colors of different particles, it can be determined whether it contains single grains with the same orientation. Then, by observing and measuring the EBSD or SEM image, the particle size of the selected single grains with the same orientation (i.e., the length of the longest axis of a single grain) can be determined.

[0162] The electrochemical performance of the material was evaluated using a button half-cell. The specific steps are as follows:

[0163] 1. Ingredients: NCM: SP: 5% PVDF glue = 9.3 g: 0.5 g: 4.0 g, NMP = 9g, stir at high speed to disperse evenly.

[0164] 2. Coating and drying: Evenly coat the slurry on 20μm thick aluminum foil with a 210um coater, set the coating length to the maximum length of the coater, cut the back half of the electrode and put it into a 100℃ forced air drying oven to dry for more than 1.5 hours.

[0165] 3. Rolling, punching and drying:

[0166] When rolling, adjust the roller machine to 1 roller gap and roll for 3 times; use a 14mm punching machine to punch holes, weigh, and place in a vacuum drying oven for vacuum drying at 85°C for more than 8 hours.

[0167] 4. Assembly of the button (LIR2016):

[0168] Positive electrode shell - 2 drops of electrolyte - positive electrode sheet (14mm) - 3 drops of electrolyte - 20μm separator - 2 drops of electrolyte - φ16*1.0mm lithium sheet - 150μm nickel foam - negative electrode shell (dried at 50℃). After the battery is assembled, seal it and take it out of the glove box for testing.

[0169] 5. Power-off test

[0170] After standing for 12 hours, perform the battery test according to the following system:

[0171] Charge at 0.1C and discharge at 0.1C for 2 weeks (initial efficiency), constant voltage cut-off current 0.005C;

[0172] Charge at 0.5C and discharge at 0.5C for 1 week (rate), constant voltage cut-off current 0.05C;

[0173] Charge at 0.5C and discharge at 1C for 1 week (rate), constant voltage cut-off current 0.05C;

[0174] Charge at 0.5C and discharge at 2C for 1 week (rate), constant voltage cut-off current 0.05C;

[0175] Charge at 0.5C and discharge at 1C for 50 weeks (cycles), constant voltage cut-off current 0.05C.

[0176] Repeat the above steps of assembling the coin cell for the coin cell high-temperature cycle retention rate test. Place the battery in an incubator at 45°C for charge and discharge tests. The steps are as follows:

[0177] After standing for 12h, conduct battery tests according to the following regime:

[0178] Charge at 0.1C and discharge at 0.1C for 2 weeks (initial efficiency), constant voltage cut-off current 0.005C;

[0179] Charge at 0.5C and discharge at 0.5C for 1 week (rate), constant voltage cut-off current 0.05C;

[0180] Charge at 0.5C and discharge at 1C for 1 week (rate), constant voltage cut-off current 0.05C;

[0181] Charge at 0.5C and discharge at 2C for 1 week (rate), constant voltage cut-off current 0.05C;

[0182] Charge at 0.5C and discharge at 1C for 50 weeks (cycles), constant voltage cut-off current 0.05C.

[0183] Repeat the above steps of assembling the coin cell for the coin cell low-temperature DCR test. Place the battery in an incubator at 25°C for charge and discharge pre-activation:

[0184] Charge at 0.1C and discharge at 0.1C for 1 week (activation), constant voltage cut-off current 0.005C;

[0185] Charge at 0.1C and discharge to 3.72V, stand still for 6h;

[0186] Discharge at 2C for 1min, take a point every 0.1s;

[0187] Finally, obtain the low-temperature DCR data through the above data processing.

[0188] Table 1 Comparison table of performance parameters of the positive electrode materials in the examples and comparative examples

[0189]

[0190] Table 2 Comparison Table of Positive Electrode Sheets of Examples and Comparative Examples

[0191]

[0192] Combined with Figures 1 to 4 It can be seen that the particle dispersibility in the positive electrode materials prepared in Examples 1 to 4 of this application is good, and there is no obvious agglomeration phenomenon. And combined with Figure 6 It can be seen that the positive electrode material in Comparative Example 1 is significantly agglomerated and has poor dispersibility.

[0193] Combined with the results of Table 1 and Table 2, it can be seen from Example 1 that for the positive electrode material of Example 1, the microcrystalline coefficient P is 20650, within the range of 20000 ≤ P ≤ 100000, indicating that there are more microcrystals in the primary particles, and there are certain gaps between the microcrystals that can provide transmission channels for lithium ions, thereby increasing the lithium ion transmission channels within the primary particles. Therefore, the DCR (Direct Current Resistance) can be reduced, and the capacity and cycle life of the battery can be improved. At the same time, the average longest axis diameter of the positive electrode material is 2.12 μm, the primary particles of the positive electrode material are larger, and the atomic parallel spacing d in the 104 crystal plane direction 104 is 77.3 nm, indicating that there are a large number of microcrystals in the primary particles, solving the problem of insufficient growth of primary particles in traditional single crystal particles; while the material grows into large particle single crystals, the number of microcrystals in the particles is increased to enhance the ionic conductivity of the material, solving both the problem of large particle single crystal growth and the problem of high impedance and low capacity of large particle single crystals.

[0194] Combined with the results of Table 1 and Table 2, it can be seen from Examples 1-10 that in this application, a spinel structure precursor is formed by spray pyrolysis, and then the amount of lithium salt is reduced during the first sintering process to promote the doping of the high-valence element X to control the density of crystal nuclei. At the same time, the temperature of the first heat treatment is relatively low, which can promote the growth of microcrystals within the primary particles. Then, through the relatively high temperature of the second heat treatment, the growth of primary particles can be promoted, so that the microcrystalline coefficient P of the primary particles satisfies 20000 ≤ P ≤ 100000, indicating that there are more microcrystals in the primary particles, and there are certain gaps between the microcrystals that can provide transmission channels for lithium ions, thereby increasing the lithium ion transmission channels within the primary particles. Therefore, the DCR (Direct Current Resistance) can be reduced, and the capacity and cycle life of the battery can be improved. Moreover, the average value D of the length of the longest axis of the positive electrode material is > 2.0 μm, d 104The value satisfies 20 - 100 nm, indicating that the primary particles grow into large single crystals while increasing the number of microcrystals in the particles, thereby enhancing the ionic conductivity of the material, solving both the problem of the growth of large single crystals and the problem of high impedance and low capacity of large single crystals.

[0195] Combining Table 1 and Table 2, it can be seen that the precursor prepared by the co - precipitation process in Comparative Example 1 is not doped with high - valence elements. The average longest axis diameter D of the primary particles and the atomic parallel spacing in the 104 crystal plane direction are small, and the microcrystalline coefficient P < 20000, indicating that the primary particles are small and there are few microcrystals inside. Its DCR (Direct Current Resistance) is high, and the capacity and cycle life of the battery are poor.

[0196] Combining Table 1 and Table 2, it can be seen that the precursor prepared by the co - precipitation process in Comparative Example 2 is doped with high - valence elements. The high - valence elements inhibit the growth of primary particles. The average longest axis diameter D of the primary particles and the atomic parallel spacing in the 104 crystal plane direction are small, and the microcrystalline coefficient P < 20000, indicating that the primary particles are small and there are few microcrystals inside. Its DCR (Direct Current Resistance) is high, and the capacity and cycle life of the battery are poor.

[0197] Combining Table 1 and Table 2, it can be seen that the precursor in Comparative Example 3 is prepared by spray pyrolysis and is not doped with high - valence elements. Without doping with high - valence elements, the average longest axis diameter D of the primary particles obtained in Comparative Example 3 and the atomic parallel spacing in the 104 crystal plane direction are small, and the microcrystalline coefficient P < 20000, indicating that the primary particles are small and there are few microcrystals inside. Its DCR (Direct Current Resistance) is high, and the capacity and cycle life of the battery are poor.

[0198] The above has introduced the embodiments of the present application in detail. Specific examples are used in this article to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application. At the same time, changes or deformations made by those skilled in the art based on the idea of the present application, within the specific implementation manner and application scope of the present application, all belong to the protection scope of the present application. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A positive electrode material, the positive electrode material is a lithium nickel cobalt composite oxide, the positive electrode material comprises a plurality of crystal grains, the crystal grains comprise primary particles, characterized in that: The positive electrode material has a primary particle crystallite coefficient P, , the crystallite coefficient P satisfies 20000≤P≤100000; wherein, d 104 is the atomic parallel spacing of the 104 crystal plane, i.e., the crystallite size, and the d 104 20-100nm; D is the length of the average longest axis of the primary particles, and D>2.0 μm.

2. The positive electrode material according to claim 1, characterized in that The positive electrode material satisfies at least one of the following conditions: a) In the XRD spectrum of the positive electrode material, there is a first peak between 17°-20° of 2θ, and the half-peak width of the first peak is 0.08-0.20, and there is a second peak between 42°-45° of 2θ, and the half-peak width of the second peak is 0.10-0.30; b) The positive electrode material has an atomic parallel spacing d of 003 crystal planes 003 , d 003 It is 80-160nm.

3. The positive electrode material according to claim 1, characterized in that The grains have the same orientation, and the length of the longest axis of the grains is 1 μm-5 μm.

4. The positive electrode material according to claim 1, characterized in that The positive electrode material has a chemical formula of Li a Ni x M y N z X 1-x-y-z O 2b , wherein 0.98≤a≤1.05, 0.60≤x<1, 0<y≤0.40, 0≤z≤0.003, 0.95≤b≤1.05; M is selected from at least one of Co, Mn, and Al, N is selected from one or more of Ti, Zr, Mg, Sr, Ba, Nb, B, W, and Al, and X is selected from one or more of W, Y, Mn, Os, Sb, and V.

5. The positive electrode material according to claim 4, characterized in that The crystal grain comprises an inner region, the distance between any point in the inner region and the surface of the crystal grain is greater than 500 nm, and at least part of the element X is located in the inner region.

6. The positive electrode material according to any one of claims 1 to 5, wherein the positive electrode material satisfies at least one of the following conditions: a) Powder resistivity of the positive electrode material ; b) The compaction density of the positive electrode material is ≥3.00 g / cc.

7. The positive electrode material according to any one of claims 1 to 5, wherein the positive electrode material satisfies at least one of the following conditions: a) The volume distribution median particle size D50 of the positive electrode material satisfies: 3 um <D50<5um; b) the volume particle size distribution width of the positive electrode material is span, , the span value satisfies: 1.0≤Span≤1.

8.

8. The positive electrode material according to claim 1, characterized in that The ratio of the discharge capacity of the positive electrode material at 0.1C to the charge capacity is ≥90.0%, and the ratio of the discharge capacity of the positive electrode material at 0.5C to the discharge capacity at 0.1C is ≥96.5%.

9. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode material according to any one of claims 1 to 8.

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