Metal oxide precursor, preparation method therefor, and use thereof

Abstract

Disclosed in the present application are a metal oxide precursor, a preparation method therefor, and the use thereof. The metal oxide precursor is of a monocrystalline structure. In a cumulative particle size distribution curve function f(x) of the metal oxide precursor, f(x) is the cumulative particle size distribution, 0<f(x)<100%, x being the particle size, and 0.05μm<x<20μm. When f(x1)=25% and f(x2)=75%, n particle size values are present between x1 and x2, and the average value of tangent slopes of the points corresponding to the x1, the x2 and the n particle size values in the cumulative particle size distribution curve is K', and K'>25, wherein n>0, the tangent slope of the points is K, and K is the derivative of the cumulative particle size distribution curve function f(x) of the metal oxide precursor. The metal oxide precursor of the present application has monocrystalline structure, excellent particle size distribution uniformity and high sintering activity and uniformity, and helps to improve the discharge capacity and cycle performance of positive electrode materials.

Description

Metal Oxide Precursor, Its Preparation Method and Application

[0001] This application claims the priority of a Chinese patent application with the application number 202311873876.2 and the invention title "Metal Oxide Precursor, Its Preparation Method and Application", which was filed with the Chinese Patent Office on December 29, 2023. The entire content is incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and particularly to a metal oxide precursor, its preparation method and application. Background Art

[0003] Currently, the precursors prepared by the mainstream co-precipitation method are usually secondary particle aggregates, which can only sinter polycrystalline cathodes. During the charge and discharge process of polycrystalline cathode materials, alkali metal ions enter and exit, causing individual crystals to expand and contract, generating stress in grain boundaries, resulting in grain boundary tearing and a decline in cycle performance.

[0004] The single-crystal structure precursors prepared by traditional spray methods usually have the characteristics of relatively large primary particle size, uneven particle size, and regular octahedral structure. However, the single-crystal structure precursors based on these characteristics have the following problems: (1) They are prone to breakage during the compaction process; (2) The sintering activity is reduced, resulting in a long sintering time and high energy consumption; (3) Due to uneven particle size, the sintering is uneven, leading to poor electrochemical performance of the cathode material.

[0005] Application Content

[0006] One of the objectives of the embodiments of this application is to provide a metal oxide precursor, its preparation method and application, aiming to solve the problems of easy breakage during the compaction process, uneven particle size, reduced sintering activity, and uneven sintering of single-crystal structure precursors.

[0007] The technical solution adopted in the embodiments of this application is as follows:

[0008] In the first aspect, a metal oxide precursor for preparing a cathode material is provided. The metal oxide precursor has a single-crystal structure. In the cumulative particle size distribution curve function f(x) of the metal oxide precursor, f(x) is the cumulative particle size distribution, 0 < f(x) < 100%, x is the particle size, and 0.05 μm < x < 20 μm;

[0009] When f(x1) = 25% and f(x2) = 75%, there are n particle size values ​​between x1 and x2, where n is the number of particle size values ​​between x1 and x2, and n>0; the average value of the tangent slopes of the corresponding point values ​​of x1, x2 and n particle size values ​​in the cumulative particle size distribution curve is K′, and K′>25, wherein the tangent slope of the point value is K, and K is the derivative of the cumulative particle size distribution curve function f(x) of the metal oxide precursor.

[0010] In some embodiments, in the cumulative particle size distribution curve of the metal oxide precursor, the horizontal axis is the logarithmic scale of the particle size x of the metal oxide precursor, marked as log 10 (x), the ordinate is the cumulative volume fraction of the metal oxide precursor corresponding to the particle size condition of the abscissa, marked as f(x).

[0011] In some embodiments, the average value K′ of the tangent slopes of x1, x2 and the n particle size values ​​corresponding to the point values ​​in the cumulative particle size distribution curve is calculated as follows: Among them, K1, K2, K n The granularity is x1, x n The cumulative particle size distribution curve functions f(x1), f(x2), f(x n ), the particle size x n is a particle size value between the particle size x1 and the particle size x2.

[0012] In some embodiments, the angle between the straight line with a slope of K′ and the x-axis is θ1, and 87.7°≤θ1≤90°.

[0013] In some embodiments, the angle between the straight line with a slope of K′ and the y-axis is θ2, and θ2 / 90°<0.024.

[0014] In some embodiments, the metal oxide precursor D 50 0.5μm-2.5μm.

[0015] In some embodiments, the metal oxide precursor D min 0.05μm-0.3μm.

[0016] In some embodiments, the metal oxide precursor D max 5μm-20μm.

[0017] In some embodiments, the specific surface area of ​​the metal oxide precursor is 8m 2 / g-15m 2 / g.

[0018] In some embodiments, the primary particles of the metal oxide precursor include an octahedral-like structure and / or a spherical-like structure.

[0019] In some embodiments, the primary particles have a particle size of 50 nm to 500 nm.

[0020] In some embodiments, the metal oxide precursor has a general chemical formula of Mn a M 1-a O2, wherein 0.1≤a≤0.9, and M is selected from at least one of Ni, Fe, Cu, and Zn.

[0021] In a second aspect, the present application provides a method for preparing the above-mentioned metal oxide precursor, wherein the preparation method is selected from the spray pyrolysis method.

[0022] In some embodiments, the pyrolysis temperature of the spray pyrolysis method is 600°C-900°C.

[0023] In some embodiments, the atomization pressure of the spray pyrolysis method is 0.4 MPa-0.6 MPa.

[0024] In some embodiments, the air-fuel ratio of the spray pyrolysis method is 15-20.

[0025] In a third aspect, the present application provides a positive electrode material, which is prepared using the metal oxide precursor prepared by the above method or the above metal oxide precursor.

[0026] In a fourth aspect, the present application provides a positive electrode sheet comprising a positive electrode current collector and a positive electrode material layer disposed on a surface of the positive electrode current collector, wherein the positive electrode material layer comprises the above-mentioned positive electrode material.

[0027] In a fifth aspect, the present application provides a secondary battery comprising the above-mentioned positive electrode sheet.

[0028] The metal oxide precursor of the present application, on the one hand, since the cumulative particle size distribution curve function of the metal oxide precursor f(x1) = 25%, f(x2) = 75%, the average value K′ of the tangent slope of the corresponding point values ​​at x1, x2 and n particle size values ​​between x1 and x2 in the cumulative particle size distribution curve is greater than 25, so that the metal oxide precursor not only has a narrow normal particle size distribution, but also has a high uniformity of particle size distribution, and is easier to embed alkali metal ions when sintering the positive electrode material, so that the sintering activity is high and the sintering uniformity is good, and thus the positive electrode material can easily obtain a higher discharge capacity; on the other hand, since the metal oxide precursor does not have problems such as grain boundaries and has a high compressive resistance, the positive electrode material made from the metal oxide precursor can be made more structurally stable and not easily broken during the compaction process, which is beneficial to improving the cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or exemplary technical descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0030] FIG1 is a graph showing the cumulative particle size distribution of metal oxide precursors in some embodiments of the present application;

[0031] FIG2 is a scanning electron microscope image of the metal oxide precursor prepared in Example 1 of the present application;

[0032] FIG3 is a particle size distribution curve of the metal oxide precursor obtained in Example 1 of the present application, wherein A is the volume particle size distribution curve and B is the cumulative particle size distribution curve;

[0033] FIG4 is a scanning electron microscope image of the positive electrode material prepared in Example 1 of the present application;

[0034] FIG5 is a scanning electron microscope image of the metal oxide precursor prepared in Comparative Example 1 of the present application;

[0035] FIG6 is a particle size distribution curve of the metal oxide precursor obtained in Comparative Example 1 of the present application, wherein A is the volume particle size distribution curve and B is the cumulative particle size distribution curve;

[0036] FIG7 is a scanning electron microscope image of the positive electrode material prepared in Comparative Example 1 of the present application;

[0037] FIG8 is a scanning electron microscope image of the metal oxide precursor prepared in Comparative Example 3 of the present application;

[0038] FIG9 is a particle size distribution curve of the metal oxide precursor obtained in Comparative Example 3 of the present application, wherein A is the volume particle size distribution curve and B is the cumulative particle size distribution curve;

[0039] FIG10 is a scanning electron microscope image of the positive electrode material prepared in Comparative Example 3 of the present application;

[0040] Figure 11 is a charge and discharge performance test graph of the positive electrode materials prepared in Example 1 and Comparative Examples 1 to 3 of the present application, wherein A is the charge and discharge performance curve of the positive electrode material prepared in Example 1, B is the charge and discharge performance curve of the positive electrode material prepared in Comparative Example 1, C is the charge and discharge performance curve of the positive electrode material prepared in Comparative Example 1, and D is the charge and discharge performance curve of the positive electrode material prepared in Comparative Example 1;

[0041] Figure 12 is a cycle performance test diagram of the positive electrode materials prepared in Example 1 of the present application and Comparative Examples 1 to 3, wherein A is the specific capacity change of the positive electrode material prepared in Example 1 at different cycle numbers, B is the specific capacity change of the positive electrode material prepared in Comparative Example 1 at different cycle numbers, C is the specific capacity change of the positive electrode material prepared in Comparative Example 1 at different cycle numbers, and D is the specific capacity change of the positive electrode material prepared in Comparative Example 1 at different cycle numbers. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit this application.

[0043] It should be noted that when a component is referred to as being "fixed on" or "disposed on" another component, it may be directly on the other component or indirectly on the other component. When a component is referred to as being "connected to" another component, it may be directly or indirectly connected to the other component. The terms "upper", "lower", "left", "right", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of description and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on this application. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances. The terms "first" and "second" are only used for the purpose of convenience of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the technical field of the present application. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments or embodiments and are not intended to limit the present application. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0045] In order to illustrate the technical solution described in this application, the following is a detailed description with reference to specific drawings and embodiments.

[0046] Some embodiments of the present application provide a metal oxide precursor. The metal oxide precursor has a single crystal structure. In the cumulative particle size distribution curve function f(x) of the metal oxide precursor, f(x) is the cumulative particle size distribution, 0 < f(x) < 100%, x is the particle size, and 0.05 μm < x < 20 μm.

[0047] Combined with the cumulative particle size distribution curve diagram of the metal oxide precursor in an embodiment shown in FIG. 1, taking FIG. 1 as an example, the abscissa in the cumulative particle size distribution curve function f(x) represents the particle size. However, due to the large particle size distribution range, directly using the original particle size as the abscissa will make the curve too concentrated. Therefore, the logarithmic scale (log 10 ) is used as the abscissa. If the particle size is d, then at the logarithmic scale, this particle size is represented as log 10 (d); the ordinate represents the cumulative volume percentage corresponding to the particle size of the abscissa, marked as f(x). In the conventional linear coordinates, the particle size values of the abscissa are too far apart, while in the logarithmic coordinates, the distances of these points are equally distributed on the logarithmic coordinates, reducing the differences within the large value range and enabling better observation of the details within different order-of-magnitude ranges. As can be seen from FIG. 1, the larger the abscissa log 10 (d) (i.e., the larger the x particle size), the cumulative volume percentage f(x) shows a trend of first increasing and then stabilizing. This is because: in the embodiments of the present application, the cumulative volume distribution reflects the total proportion of all particles from the smallest size to the current size; when the particle size is small, the cumulative distribution grows slowly because the proportion of particles with small volumes in the total volume is small; when the particle size becomes larger, the presence of larger particles will increase the cumulative volume distribution. Especially in the "middle section" of the particle distribution, there are more of these particles, so the cumulative volume distribution grows faster. After reaching a particle size value, the growth slows down because at this time, the volume proportion of particles with large particle sizes is already relatively high, and the proportion of these large particle sizes in the material no longer increases significantly, resulting in the slowdown of growth.

[0048] When f(x1) = 25% and f(x2) = 75%, there are n particle size values between x1 and x2, where n > 0. The tangent slopes of the corresponding point values of x1, x2, and the n particle size values in the cumulative particle size distribution curve are K. K is the derivative of the cumulative particle size distribution curve function f(x) of the metal oxide precursor. That is, the tangent slopes of the corresponding point values of x1 and x2 in the cumulative particle size distribution curve are K1 and K2 respectively, and the tangent slopes of the corresponding point values of the n particle size values in the cumulative particle size distribution curve are K n , K1, K2, K n are the derivatives of the cumulative particle size distribution curve functions f(x1), f(x2), and f(x n ) of the metal oxide precursor with particle sizes of x1, x2, and x n respectively. Therefore, the average value Where n is the number of granularity values ​​between x1 and x2, and granularity x n It is the particle size value between particle size x1 and particle size x2.

[0049] The metal oxide precursor of the present application, on the one hand, since the cumulative particle size distribution curve function of the metal oxide precursor is f(x1) = 25%, f(x2) = 75%, the average value K′ of the tangent slope of the corresponding point value in the cumulative particle size distribution curve of n particle size values ​​between x1, x2 and x1 to x2 is greater than 25, so that the metal oxide precursor not only has a narrow normal particle size distribution, but also has a high particle size distribution uniformity, which makes it easier to embed alkali metal ions when sintering the positive electrode material, so that the sintering activity is high and the sintering uniformity is good, thereby making it easy for the positive electrode material to obtain a higher discharge capacity. The cumulative particle size distribution curve function of the embodiment of the present application is f(x1) = 25% to f(x2) = 75%, that is, corresponding to a particle size of D 25 ~D 75 The interval includes the D 50 The median particle size excludes the influence of extreme particles that are abnormally large or small. The range of f(x) from 25% to 75% reflects both the central trend and the degree of dispersion of the distribution, and is very representative.

[0050] On the other hand, the metal oxide precursor that meets the above conditions is a single crystal particle, the grain orientation is consistent, there is no grain boundary inside it, there are fewer defects during the growth process, and it is not easy to produce cracks and micro defects when under pressure, thereby improving the overall strength and compression resistance of the material. It avoids the problem that in polycrystalline materials, the orientation of different grains will produce inconsistent responses in the direction of force, and stress concentration will occur at the grain boundaries and cause rupture. Since the metal oxide precursor of the embodiment of the present application does not have problems such as grain boundaries, and has a higher compression resistance, the positive electrode material structure stability made by the metal oxide precursor can be made stronger, and it is not easy to break during the compaction process, which is conducive to improving the cycle performance. In addition, the metal oxide precursor also has good structural inheritance and is easy to prepare a positive electrode material with a single crystal structure.

[0051] For example, the value of x can be any typical but non-limiting point value such as 0.05 μm, 1 μm, 2 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, or an interval value between any two point values.

[0052] In some embodiments, as shown in FIG1 , the angle θ1 between the straight line with a slope of K′ and the x-axis is 87.7°≤θ1≤90°. K′ and θ1 are positively correlated. A larger θ1 value indicates a steeper slope of the straight line with a slope of K′, i.e., a larger K′ value results in a more uniform particle size distribution of the metal oxide precursor. For example, the angle θ1 between the straight line with a slope of K′ and the x-axis can be any typical but non-limiting value such as 87.7°, 88°, 88.5°, 89°, 89.5°, 90°, or an interval between any two values.

[0053] In some embodiments, the angle between the straight line with a slope of K' and the y-axis is θ2, where θ2 / 90° is less than 0.024. Since θ1+θ2=90°, θ2 / 90°=(90°-θ1) / 90°, (90°-θ1) / 90° represents the particle uniformity μ of the metal oxide precursor, i.e., μ<0.024. The closer the μ value is to 0, the more uniform the particle size of the metal oxide precursor. For example, the angle between the straight line with a slope of K' and the y-axis is θ2, and θ2 / 90° can be any typical but non-limiting value, such as 0.023 μm, 0.022 μm, 0.02 μm, 0.018 μm, 0.015 μm, 0.012 μm, 0.01 μm, 0.005 μm, or an interval between any two values.

[0054] In some embodiments, the D of the metal oxide precursor 50 0.5 μm-2.5 μm; exemplary values ​​may be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, and other typical but non-limiting arbitrary point values ​​or interval values ​​between any two point values. 50 Also called median diameter.

[0055] In some embodiments, the metal oxide precursor is min 0.05 μm-0.3 μm; exemplary values ​​may be 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, and other typical but non-limiting arbitrary point values ​​or interval values ​​between any two point values. min Indicates the minimum particle diameter in a particle group.

[0056] In some embodiments, the D of the metal oxide precursor max 5 μm-20 μm; exemplary values ​​may be 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, and other typical but non-limiting arbitrary point values ​​or interval values ​​between any two point values. max Indicates the maximum particle diameter in the particle group.

[0057] In some embodiments, the specific surface area of ​​the metal oxide precursor is 8 m 2 / g-15m 2 / g; an example may be 8m 2 / g、9m 2 / g、10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g、15m 2 / g etc. are typical but non-restrictive arbitrary point values ​​or interval values ​​between any two point values.

[0058] The above embodiments of the present application define D 50 、D min 、D max and specific surface area, so that the metal oxide precursor has a smaller particle size and a higher specific surface area while meeting the specific narrow normal particle size distribution and high particle size distribution uniformity, which is beneficial to improving the sintering activity and significantly shortening the preparation time, thereby reducing the energy consumption in preparing the positive electrode material.

[0059] In some embodiments, the primary particles of the metal oxide precursor include an octahedral structure and / or a spherical structure. In some embodiments, the particle size of the primary particles is 50nm-500nm, and exemplary values ​​may be 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, or any other typical but non-restrictive point values ​​or interval values ​​between any two point values. Compared with the traditional fully developed spinel structure, the metal oxide precursor of the present application requires less energy consumption and lower cost for preparing positive electrode materials, and small particles with high distribution uniformity are easier to embed sodium ions during sintering, which is beneficial to improving sintering activity.

[0060] In some embodiments, the metal oxide precursor has the general chemical formula Mn a M 1-a O2, wherein 0.1≤a≤0.9, and M is selected from at least one of Ni, Fe, Cu, and Zn. It is understood that the metal oxide precursor of the present application may be a binary metal oxide, a ternary metal oxide, or a quaternary metal oxide, and this application is not limited thereto. For example, a may be any typical but non-limiting value such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9, or an interval between any two values.

[0061] The present application provides a method for preparing the above metal oxide precursor, wherein the preparation method is selected from spray pyrolysis.

[0062] It should be noted that the specific operation of the spray pyrolysis method can refer to the existing method, and this application will not go into details.

[0063] In some embodiments, the pyrolysis temperature of the spray pyrolysis method is 600°C-900°C; exemplary values ​​may be 600°C, 700°C, 800°C, 900°C, or any other typical but non-limiting values, or an interval between any two values.

[0064] In some embodiments, the atomization pressure of the spray pyrolysis method is 0.4 MPa-0.6 MPa; exemplary values ​​may be 0.4 MPa, 0.5 MPa, 0.6 MPa, or any other typical but non-limiting values, or an interval between any two values.

[0065] In some embodiments, the air-fuel ratio of the spray pyrolysis method is 15-20, and can be 15, 16, 17, 18, 19, 20, or any other typical but non-limiting value, or an interval between any two values. The air-fuel ratio is the mass ratio of air to fuel in the mixed gas.

[0066] By adjusting the spray pyrolysis temperature, atomization pressure, air-fuel ratio and other conditions, it is beneficial to improve the particle size distribution effect of the obtained metal oxide precursor, so that the metal oxide precursor has the characteristics of single crystal structure, excellent particle size distribution uniformity and good structural inheritance.

[0067] The present application also provides a positive electrode material prepared from the above metal oxide precursor.

[0068] When the metal oxide precursor of the present application is used to prepare a positive electrode material, it is easier to obtain a single crystal positive electrode material with good uniformity, which is beneficial to improving the discharge capacity and cycle performance of the positive electrode material.

[0069] It should be noted that the preparation method of the positive electrode material refers to the existing method, and this application will not go into details.

[0070] The present application also provides a positive electrode sheet and a secondary battery comprising a positive electrode material, which can be specifically a sodium ion battery. The positive electrode material includes a positive electrode collector and a positive electrode material layer arranged on the surface of the positive electrode collector, and the positive electrode material layer includes the above positive electrode material.

[0071] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector, for example, aluminum foil is used as the metal foil; the composite current collector may be formed by forming a metal material on a polymer material substrate, wherein the metal material includes but is not limited to at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, and the polymer material substrate includes but is not limited to at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0072] It can be understood that the positive electrode material layer also includes a binder and a conductive agent, wherein the binder can be any commercially available binder for positive electrode sheets, including but not limited to polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-fluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and at least one of fluorine-containing acrylate resins, or a binder prepared by any prior art, and this application is not limited thereto; the conductive agent can be any commercially available conductive agent for sodium ion batteries, such as carbon black, graphite, etc.

[0073] The metal oxide precursors, their preparation methods, and applications are further described below through the following specific examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present application and should not be construed as limiting the scope of the present application. Where specific conditions are not specified in the examples, conventional conditions or those recommended by the manufacturer were followed. Reagents or instruments used, for which the manufacturer is not specified, are commercially available conventional products.

[0074] Example 1

[0075] Nickel salt, iron salt and manganese salt are prepared into a mixed metal salt solution in a metal atomic molar ratio of 4:4:2, and then the mixed metal salt solution is introduced into a roasting furnace in the form of droplets under an atomization pressure of 0.4 MPa. The air-fuel ratio in the roasting furnace is 15. Under a pyrolysis temperature of 600°C, the droplets are evaporated, dried, thermally decomposed and sintered to form a metal oxide precursor. The obtained metal oxide precursor product is simply represented by NFM442.

[0076] The surface morphology of the metal oxide precursor prepared in this embodiment is shown in FIG2 . It can be seen that the metal oxide precursor is a single crystal structure with an octahedral structure and some small spherical structures. min About 0.07μm, D 50 About 0.54μm, D max The surface area is about 6.7 μm and the specific surface area is about 13.7 m 2 / g, and the particle size of primary particles is about 50nm-300nm.

[0077] The volume and cumulative particle size distribution curves of the metal oxide precursor prepared in this example are shown in Figure 3. This metal oxide precursor exhibits an extremely narrow particle size distribution, and the cumulative distribution curve has a steep slope, indicating uniform particle size. Calculations show that K' of this metal oxide precursor is 26.1, θ1 is 87.8°, and μ is 0.024, indicating a very uniform particle size distribution.

[0078] The metal oxide precursor prepared in this example was mixed with sodium carbonate in a molar ratio of 1:1, and then placed in a muffle furnace. The temperature was raised to 900°C at a heating rate of 5°C / min in an air atmosphere. After constant temperature sintering for 15 hours, the mixture was naturally cooled, crushed, and sieved to obtain a positive electrode material having a chemical formula of Na(Ni 0.4 Fe 0.4 Mn 0.2 The surface morphology of the cathode material prepared in this embodiment is shown in FIG4 , which shows that the cathode material is a hexagonal prism structure of uniform size and has a smooth surface, indicating that there is no residual alkali on the surface.

[0079] Example 2

[0080] Nickel salt, copper salt, iron salt and manganese salt are prepared into a mixed metal salt solution in a metal atomic molar ratio of 24:5:36:35, and then the mixed metal salt solution is introduced into a roasting furnace in the form of droplets under an atomization pressure of 0.5 MPa. The air-fuel ratio in the roasting furnace is 18. Under a pyrolysis temperature of 800°C, the droplets are evaporated, dried, thermally decomposed and sintered to form a metal oxide precursor. The obtained metal oxide precursor product is simply expressed as NCFM24 / 5 / 36 / 35.

[0081] After testing, the D min About 0.2μm, D 50 About 1.53μm, D max The surface area is about 17.4 μm and the specific surface area is about 9.48 m 2 / g, and the particle size of primary particles is about 60nm-400nm.

[0082] Calculations show that K′ of the metal oxide precursor is 30, θ1 is 88.1°, and μ is 0.021, indicating that the particle size distribution of the metal oxide precursor is very uniform.

[0083] The metal oxide precursor prepared in this example was mixed with sodium carbonate in a molar ratio of 1:1, and then placed in a muffle furnace. The temperature was raised to 900°C at a heating rate of 5°C / min in an air atmosphere. After constant temperature sintering for 15 hours, the mixture was naturally cooled, crushed, and sieved to obtain a positive electrode material having a chemical formula of Na(Ni 0.24 Cu 0.05 Fe 0.36 Mn 0.35 )O2.

[0084] Example 3

[0085] Copper salt, iron salt and manganese salt are prepared into a mixed metal salt solution in a metal atomic molar ratio of 2:3:5, and then the mixed metal salt solution is introduced into a roasting furnace in the form of droplets under an atomization pressure of 0.6 MPa. The air-fuel ratio in the roasting furnace is 20. Under a pyrolysis temperature of 900°C, the droplets are evaporated, dried, thermally decomposed and sintered to form a metal oxide precursor. The obtained metal oxide precursor product is simply expressed as CFM235.

[0086] After testing, the D min About 0.27μm, D 50 About 2.39μm, D max The surface area is about 19.6 μm and the specific surface area is about 8.9 m 2 / g, and the particle size of the primary particles is about 65nm-450nm.

[0087] Calculations show that K′ of the metal oxide precursor is 52, θ1 is 88.9°, and μ is 0.012, indicating that the particle size distribution of the metal oxide precursor is very uniform.

[0088] The metal oxide precursor prepared in this example was mixed with sodium carbonate in a molar ratio of 1:1, and then placed in a muffle furnace. The temperature was raised to 900°C at a heating rate of 5°C / min in an air atmosphere. After constant temperature sintering for 15 hours, the mixture was naturally cooled, crushed, and sieved to obtain a positive electrode material having a general chemical formula of Na(Cu 0.2 Fe 0.3 Mn 0.5 )O2.

[0089] Comparative Example 1

[0090] Nickel salt, iron salt and manganese salt are prepared into a mixed metal salt solution in a metal atomic molar ratio of 4:4:2, and then the mixed metal salt solution is introduced into a roasting furnace in the form of droplets under an atomization pressure of 0.7 MPa. The air-fuel ratio in the roasting furnace is 23. Under a pyrolysis temperature of 950°C, the droplets are evaporated, dried, thermally decomposed and sintered to form a metal oxide precursor. The obtained metal oxide precursor product is simply represented by NFM442.

[0091] The surface morphology of the metal oxide precursor prepared in this comparative example is shown in FIG5 . It can be seen that the metal oxide precursor is still a single crystal structure, and its morphology is an octahedral structure, but the particle size is very uneven. min About 0.32μm, D 50 About 5.1μm, D max The surface area is about 30.58 μm and the specific surface area is about 5.32 m 2 / g, and the particle size of primary particles is about 600nm-1200nm.

[0092] The volume particle size distribution curve and cumulative particle size distribution curve of the metal oxide precursor prepared in this comparative example are shown in Figure 6. The volume particle size distribution curve of the metal oxide precursor exhibits a bimodal distribution, a broad particle size distribution curve, and a small cumulative distribution curve slope, indicating poor particle size uniformity. Calculations indicate that K′, θ1, and μ for this metal oxide precursor are 13.7, 85.8°, and 0.046.

[0093] The metal oxide precursor prepared in this comparative example was mixed with sodium carbonate in a molar ratio of 1:1, and then placed in a muffle furnace. In an air atmosphere, the temperature was raised to 900°C at a heating rate of 5°C / min, and constant temperature sintered for 15 hours. After natural cooling, the positive electrode material was crushed and sieved to obtain a positive electrode material with a chemical formula of Na(Ni 0.4 Fe 0.4 Mn 0.2 The surface morphology of the positive electrode material prepared in this comparative example is shown in FIG7 . It can be seen that the positive electrode material has a hexagonal prism structure, and the particle surface is rough and has a large amount of surface residual alkali, which makes the surface of the positive electrode material unstable and has an adverse effect on the cycle performance and safety of the battery.

[0094] Comparative Example 2

[0095] Nickel salt, iron salt and manganese salt are prepared into a mixed metal salt solution in a metal atomic molar ratio of 4:4:2, and then the mixed metal salt solution is introduced into a roasting furnace in the form of droplets under an atomization pressure of 0.3 MPa. The air-fuel ratio in the roasting furnace is 13. Under a pyrolysis temperature of 550°C, the droplets are evaporated, dried, thermally decomposed and sintered to form a metal oxide precursor. The obtained metal oxide precursor product is simply represented by NFM442.

[0096] The metal oxide precursor was found to still have a single crystal structure, but the particles were smaller and incompletely developed. Some of them were octahedral structures, and some amorphous small particles were seriously agglomerated and had very uneven sizes. min About 0.03μm, D 50 About 0.49μm, D max The surface area is about 4.65 μm and the specific surface area is about 18.93 m 2 / g, and the particle size of the primary particles is about 20nm-200nm.

[0097] Calculations show that the K′ of the metal oxide precursor is 12, θ1 is 85.2°, and μ is 0.053.

[0098] The metal oxide precursor prepared in this comparative example was mixed with sodium carbonate in a molar ratio of 1:1, and then placed in a muffle furnace. In an air atmosphere, the temperature was raised to 900°C at a heating rate of 5°C / min, and constant temperature sintered for 15 hours. After natural cooling, the positive electrode material was crushed and sieved to obtain a positive electrode material with a chemical formula of Na(Ni 0.4 Fe 0.4 Mn 0.2 )O2.

[0099] Comparative Example 3

[0100] Nickel salt, iron salt and manganese salt are prepared into a metal salt solution with a total molar concentration of 2 mol / L according to the metal atomic molar ratio of 4:4:2. Then, sodium hydroxide solution and ammonia solution are added to the reactor as a precipitant and a complexing agent, respectively. Nitrogen is introduced as a protective gas. The temperature is kept constant at 55°C, the pH value is controlled at 11, the stirring rate is 500 r / min, the coprecipitation reaction is carried out for 15 hours, and then the metal hydroxide precursor is obtained by centrifugal washing and drying.

[0101] The surface morphology of the metal hydroxide precursor prepared in this comparative example is shown in FIG8 . It can be seen that the metal hydroxide precursor is a polycrystalline structure. The secondary particles formed by the agglomeration of primary particles are spherical in shape and the particle size is very uneven. min About 0.51μm, D 50 About 5.3μm, D maxThe surface area is about 11.94 μm and the specific surface area is about 6.5 m 2 / g.

[0102] The volume particle size distribution curve and cumulative particle size distribution curve of the metal hydroxide precursor prepared in this comparative example are shown in FIG9 . Calculation shows that K′ of the metal hydroxide precursor is 16.4, θ1 is 86.5°, and μ is 0.038.

[0103] The metal hydroxide precursor prepared in this comparative example was mixed with sodium carbonate in a molar ratio of 1:1, and then placed in a muffle furnace. In an air atmosphere, the temperature was raised to 900°C at a heating rate of 5°C / min, and constant temperature sintered for 15 hours. After natural cooling, the mixture was crushed and sieved to obtain a positive electrode material with a general chemical formula of Na(Ni 0.4 Fe 0.4 Mn 0.2 )O2. The surface morphology of the positive electrode material prepared in this comparative example is shown in FIG10 .

[0104] The positive electrode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were made into sodium ion button batteries. The first discharge specific capacity under the voltage condition of 2V-4.15V was tested, and the capacity retention rate after 50 cycles was tested. The test results are shown in Figures 11, 12 and Table 1.

[0105] Table 1

[0106] As shown in Figures 11 and 12 and Table 1, the cathode materials prepared in Examples 1 to 3 exhibit high initial discharge specific capacities under voltage conditions of 2V-4.15V, reaching a maximum of approximately 172.3 mAh / g. Furthermore, the capacity retention rates after 50 cycles are all maintained above 90%, with a maximum of approximately 95.6%. In contrast, the initial discharge specific capacities and capacity retention rates after 50 cycles for Comparative Examples 1 to 3 are significantly lower than those in Example 1.

[0107] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The above are merely optional embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included within the scope of the claims of the present application.

Claims

1. A metal oxide precursor for preparing a cathode material, characterized in that, The metal oxide precursor is of a single crystal structure. In the cumulative particle size distribution curve function f(x) of the metal oxide precursor, f(x) is the cumulative particle size distribution, 0 < f(x) < 100%, x is the particle size, and 0.05 μm < x < 20 μm; When f(x1) = 25% and f(x2) = 75%, there are n particle size values between x1 and x2, where n is the number of particle size values between x1 and x2 and n > 0; the average value of the tangent slopes of the corresponding point values of x1, x2, and the n particle size values in the cumulative particle size distribution curve is K′, and K′ > 25, where the tangent slope of the point value is K, and K is the derivative of the cumulative particle size distribution curve function f(x) of the metal oxide precursor.

2. The metal oxide precursor according to claim 1, characterized in that, In the cumulative particle size distribution curve of the metal oxide precursor, the abscissa is the logarithmic scale of the particle size x of the metal oxide precursor, marked as log 10 (x), and the ordinate is the cumulative volume fraction of the metal oxide precursor corresponding to the particle size condition of the abscissa, marked as f(x).

3. The metal oxide precursor according to claim 1, wherein The calculation method of the average value K' of the tangent slopes of the corresponding point values of the x1, x2, and n particle size values in the cumulative particle size distribution curve is as follows: Where K1, K2, K n are the derivatives of the cumulative particle size distribution curve functions f(x1), f(x2), f(x n ) of the metal oxide precursors with particle sizes of x1, x n and x2 respectively, and the particle size x n is the particle size value between the particle size x1 and the particle size x2.

4. The metal oxide precursor according to claim 1, characterized in that, The angle between the line with a slope of K′ and the x-axis is θ1, and 87.7° ≤ θ1 ≤ 90°.

5. The metal oxide precursor according to claim 1 or claim 2, characterized in that, The angle between the line with a slope of K′ and the y-axis is θ2, and θ2 / 90° < 0.

024.

6. The metal oxide precursor according to claim 1, wherein The D of the metal oxide precursor 50 is 0.5 μm - 2.5 μm.

7. The metal oxide precursor according to claim 1, wherein The D of the metal oxide precursor min is 0.05 μm - 0.3 μm.

8. The metal oxide precursor according to claim 1, wherein The D of the metal oxide precursor max is 5 μm - 20 μm.

9. The metal oxide precursor according to claim 1, wherein The specific surface area of the metal oxide precursor is 8 m 2 / g - 15 m 2 / g.

10. The metal oxide precursor according to claim 1, characterized in that, The primary particles of the metal oxide precursor include an octahedron-like structure and / or a spherical-like structure.

11. The metal oxide precursor according to claim 10, wherein The particle size of the primary particles is 50 nm - 500 nm.

12. The metal oxide precursor according to claim 1, wherein The chemical general formula of the metal oxide precursor is expressed as Mn a M 1-a O2, where 0.1 ≤ a ≤ 0.9, and M is selected from at least one of Ni, Fe, Cu, and Zn.

13. A method for preparing a metal oxide precursor according to any one of claims 1 to 12, characterized in that, The preparation method is selected from spray pyrolysis.

14. The method for preparing a metal oxide precursor according to claim 13, wherein The pyrolysis temperature of the spray pyrolysis is 600°C - 900°C.

15. The method for preparing the metal oxide precursor according to claim 13, wherein The atomization pressure of the spray pyrolysis is 0.4 MPa - 0.6 MPa.

16. The method for preparing a metal oxide precursor according to claim 13, wherein, The air-fuel ratio of the spray pyrolysis is 15 - 20.

17. A cathode material, characterized in that, The positive electrode material is prepared from the metal oxide precursor prepared by the method according to any one of claims 1 to 12 or the metal oxide precursor according to any one of claims 13 to 16.

18. A positive electrode sheet, characterized in that, It includes a positive electrode current collector and a positive electrode material layer provided on the surface of the positive electrode current collector, and the positive electrode material layer includes the positive electrode material according to claim 17.

19. A secondary battery, characterized in that, It includes the positive electrode sheet according to claim 18.

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