Positive electrode material and preparation method thereof, and sodium ion battery

Abstract

The application discloses a sodium ion positive electrode material, a preparation method thereof and a sodium ion battery. x (Ni a Fe b M c Mn 1‑a‑b‑c )O2; the sodium ion positive electrode material comprises a kind of spheroids formed by a plurality of uniform size sheet-shaped particles agglomeration;Length of the sheet-shaped particle is 0.5 μm-2 μm, thickness is 50 nm-200 nm;The particle size distribution concentration degree alpha of the sodium ion positive electrode material is in the range of 0.65≤alpha≤1.25, wherein, alpha=(Dv 90 -Dv 10 ) / Dv 50 ;The spheroidicity regularity beta of the sodium ion positive electrode material is in the range of 1≤beta≤1.1, wherein, beta is Dv 50 Particle size of the spheroid long axis and short axis ratio average value of the spheroid.The sodium ion positive electrode material of the application has the advantages of narrow particle size distribution and regular shape, low specific surface area, high tap density, good processing performance and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion batteries, and more particularly to a positive electrode material, a preparation method thereof, and a sodium ion battery. BACKGROUND

[0002] In a lithium ion ternary positive electrode material, the main elements nickel, cobalt and manganese can be prepared into spherical nickel-cobalt-manganese-based precursors with narrow particle size distribution through coprecipitation, and then the lithium ion positive electrode material with narrow particle size distribution is obtained through sintering. Since the lithium ion positive electrode material has narrow particle size distribution, it has low specific surface area, high tap density and good processing performance (such as slurry mixing and coating), and is beneficial to the design of the battery scheme and the long cycle life of the lithium ion positive electrode material in the battery system.

[0003] However, the main elements of the current sodium ion positive electrode material are nickel, iron and manganese. The existing technology can only prepare irregular nickel-iron-manganese-based precursors with wide particle size distribution through coprecipitation, and then obtain the sodium ion positive electrode material through sintering. The sodium ion positive electrode material prepared by this method has the problems of high specific surface area, low tap density and poor processing performance. SUMMARY

[0004] The present application aims to overcome the above-mentioned defects in the prior art, and provides a sodium ion positive electrode material with narrow particle size distribution and regular shape and a preparation method thereof, so that the sodium ion positive electrode material has low specific surface area, high tap density and good processing performance.

[0005] To achieve the above-mentioned purpose, the first technical solution of the present application is as follows:

[0006] A positive electrode material satisfies the following characteristics (1) and (2):

[0007] (1) 0.65≤α≤1.25, wherein α=(Dv90-Dv10) / Dv50; Dv90, Dv10 and Dv50 are particle size distribution parameters of the positive electrode material;

[0008] (2) 1≤β≤1.1, wherein β is the average value of the ratio of the long axis length to the short axis length of the positive electrode material within the Dv50 particle size distribution range.

[0009] The second technical solution of the present application is as follows:

[0010] A positive electrode material includes a plurality of flaky particles, and the orientation distribution consistency parameter γ of the flaky particles ranges from 0.73 to less than 1, wherein n is the Dv 50The number of the flaky particles selected for calculation in the particle size distribution range of the positive electrode material, n≥10; θ i The angle between the length direction of the selected i-th flaky particle and the set horizontal axis in the counterclockwise direction, and the rotation angle of the set horizontal axis when the rotation of the set horizontal axis in the range of [-π / 2, π / 2] makes γ take the maximum value.

[0011] The third technical solution of the present application is as follows:

[0012] A positive electrode material, the positive electrode material satisfies the following relationship:

[0013] 0.70≤Ψ≤1.12, wherein Ψ=[2-α*β / 0.85+γ] / 2;

[0014] Wherein, α=(Dv90-Dv10) / Dv50, Dv90, Dv10 and Dv50 are particle size distribution parameters of the positive electrode material, β is the average value of the ratio of the long axis length to the short axis length of the positive electrode material at Dv50 particle size, n is the D v50 The number of the flaky particles selected for calculation in the particle size distribution range of the positive electrode material, n≥10; θ i The angle between the length direction of the selected i-th flaky particle and the set horizontal axis in the counterclockwise direction, and the rotation angle of the set horizontal axis when the rotation of the set horizontal axis in the range of [-π / 2, π / 2] makes γ take the maximum value.

[0015] The fourth technical solution of the present application is as follows:

[0016] A preparation method of a positive electrode material, comprising the following steps:

[0017] Mixing the reaction solution after the mixed reaction of the first solution and the third solution with the second solution under the condition of a protective atmosphere to obtain a nickel-iron-manganese-based precursor precipitate; the first solution comprises a soluble nickel salt, a soluble divalent iron salt and a soluble manganese salt, the second solution comprises an alkaline precipitating agent and a soluble carbonate, and the third solution comprises ammonia water and a reducing agent;

[0018] Mixing the nickel-iron-manganese-based precursor precipitate with a sodium source to obtain a mixture;

[0019] Sintering the mixture to obtain the positive electrode material.

[0020] The fifth technical solution of the present application is as follows:

[0021] A sodium ion battery comprising the positive electrode material or the positive electrode material prepared by the preparation method.

[0022] Implementing the embodiments of the present invention will have the following beneficial effects:

[0023] First, α=(Dv 90 -Dv 10 ) / Dv 50 In this formula, Dv 50 It is usually considered to be the standard particle size (Dv) 90 -Dv 10 ) / Dv 50 When the ratio is around 1, it indicates that Dv 10 Very small, close to zero, which also indicates that Dv 90 Approaching Dv 50 This indicates that Dv 90 The particle sizes of the spheroids within the range are all close to the standard particle size, and a small number of spheroids have very small particle sizes. Therefore, the particle size distribution of the cathode material in this application is concentrated and uniform, containing relatively few small-diameter particles; β is Dv 50 The average ratio of the major axis length to the minor axis length of spheroids within the particle size distribution range; when β is close to 1, it indicates that Dv 50 The spherical particles within the particle size distribution range are all close to spheres. It can be seen that the cathode material of this application is basically a sphere with a regular shape. Therefore, compared with the sodium ion cathode material of the prior art which has an irregular shape and a wide particle size distribution, the cathode material of this application has the significant effect of uniform size and regular shape. It can be deduced that the cathode material of this application also has a higher specific surface area, a lower tap density and better processing performance.

[0024] Second, the cathode material of this application is formed by growing sheet-like structures layer by layer to form spherical particles. The closer the orientation of the sheet-like structures, the smaller the gap between the layer-by-layer grown sheet-like structures, and the denser the spherical particles, the higher the consistency of the cathode material formed. That is, the cathode material has uniform size and regular shape. The closer the value of γ is to 1, the higher the consistency of the orientation distribution of the sheet-like particles.

[0025] Third, the preparation method of this application involves preparing a first solution containing a mixed salt, which allows the mixed salt to be added to the reaction vessel simultaneously, uniformly generating a co-precipitate of nickel hydroxide, iron hydroxide, and manganese hydroxide. At the same time, it avoids increasing the number of related equipment in the nickel-iron-manganese-based precursor production line.

[0026] Thirdly, by preparing a second solution comprising a soluble carbonate and an alkaline precipitant, the soluble carbonate and the alkaline precipitant are simultaneously subjected to a co-precipitation reaction, so that the carbonate ions are uniformly doped in the hydroxide co-precipitate crystal lattice. The doping of the carbonate ions can effectively improve the morphology and agglomeration mode of the hydroxide co-precipitate (i.e., the nickel-iron-manganese-based precursor precipitate). The carbonate ions occupy a larger space in the hydroxide co-precipitate crystal lattice, so that the hydroxide co-precipitate produces a certain amount of loose gap, which is beneficial to the sodium ion body phase diffusion in the subsequent mixed sodium carbonate sintering process.

[0027] Fourthly, the preparation method of the present application can inhibit the oxidation of divalent iron ions by a non-oxygen protective atmosphere and a reducing agent. The presence of divalent iron ions can form small particle size products, and uniform size flaky particles can be obtained, thereby obtaining uniform size spherical particles formed by agglomeration of the uniform size flaky particles. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0029] wherein:

[0030] Figure 1 FIG. 1 is a SEM scanning diagram of a sodium ion positive electrode material prepared in Example 1.

[0031] Figure 2 FIG. 4 is a SEM scanning diagram of a sodium ion positive electrode material prepared in Comparative Example 4. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0033] In the specific embodiments and claims, the terms "long axis" and "short axis" are a method for simplifying the explanation of the particle size significance: the "long axis" is the maximum length in the image obtained by scanning electron microscopy (SEM) test, and the "short axis" is the maximum length perpendicular to the "long axis" in the image.

[0034] An embodiment of a positive electrode material satisfies the following characteristics (1) and (2):

[0035] (1) 0.65 ≤ α ≤ 1.25, where α = (Dv 90 -Dv 10 ) / Dv 50 Dv 90 Dv 10 and Dv 50 These are the particle size distribution parameters of the cathode material;

[0036] (2) 1 ≤ β ≤ 1.1, where β is Dv 50 The average value of the ratio of the major axis length to the minor axis length of the cathode material within the particle size distribution range.

[0037] In the above implementation, α=(Dv 90 -Dv 10 ) / Dv 50 In this formula, Dv 50 It is usually considered to be the standard particle size (Dv) 90 -Dv 10 ) / Dv 50 When the ratio is around 1, it indicates that Dv 10 Very small, close to zero, which also indicates that Dv 90 Approaching Dv 50 This indicates that Dv 90 The particle size of the cathode material within the specified range is close to the standard particle size, and a small amount of cathode material has a very small particle size. Therefore, the particle size distribution of the cathode material in this application is concentrated and uniform, containing relatively few small-diameter particles; β is Dv 50 The average ratio of the major axis length to the minor axis length of spheroids within the particle size distribution range; when β is close to 1, it indicates that Dv 50 The spherical particles within the particle size distribution range are all close to spheres. It can be seen that the cathode material of this application is basically a sphere with a regular shape. Therefore, compared with the cathode material of the prior art which has an irregular shape and a wide particle size distribution, the cathode material of this application has the significant effect of uniform size and regular shape. It can be deduced that the cathode material of this application also has a higher specific surface area, a lower tap density and better processing performance.

[0038] In the above implementation, Dv 90 Dv represents the average particle size corresponding to a sodium-ion cathode material with a cumulative volume percentage of 90%. 50 Dv represents the average particle size corresponding to a sodium-ion cathode material with a cumulative volume percentage of 50%. 10The average particle size corresponding to 10% of the cumulative volume percentage of the sodium ion positive electrode material is represented. The closer the value of the particle size distribution concentration a is to 1, the narrower the particle size distribution, and the size of the secondary particles of the positive electrode material tends to be uniform. The closer the value of the sphericity regularity b is to 1, the closer the morphology of the sodium ion positive electrode material is to a sphere.

[0039] Reference Figure 2 which is an SEM scanning diagram of a sodium ion positive electrode material prepared by the prior art, from which it can be seen that the shape of the sodium ion positive electrode material is irregular, and the particle size distribution is wide. Compared with the prior art, the sodium ion positive electrode material prepared by the present application is a spherical body. Since the size of the flaky particles forming the spherical body is uniform, the spherical body formed has a regular shape (the sphericity regularity b is in the range of 1≤b≤1.1), and the size is uniform (the particle size distribution concentration a is in the range of 0.65≤a≤1.25). Therefore, compared with the sodium ion positive electrode material of the prior art which has an irregular shape and a wide particle size distribution, the present application has a higher specific surface area, a lower tap density, and better processing performance.

[0040] Another embodiment of a positive electrode material includes a plurality of flaky particles, and the orientation distribution consistency parameter g of the flaky particles is in the range of 0.73≤g<1, wherein, n is Dv 50 The number of flaky particles selected for calculation on the positive electrode material in the particle size distribution range, n≥10; θ i is the included angle between the length direction of the i-th selected flaky particle and the clockwise direction of the horizontal axis, and d is the rotation angle of the horizontal axis when g takes the maximum value.

[0041] In some embodiments, the positive electrode material includes a spherical body formed by agglomeration of a plurality of flaky particles.

[0042] In the above embodiments, the growth direction consistency of the flaky particles is characterized by the orientation distribution consistency parameter g of the flaky particles on the spherical body. The spherical body is formed by layer-by-layer growth of the flaky particles, and the higher the growth direction consistency of the flaky particles, the more regular the shape of the spherical body and the more uniform the size. In addition, the higher the growth direction consistency of the flaky particles, the more unobstructed the conductive channel, and the better the electrical performance of the sodium ion positive electrode material.

[0043] Reference Figure 1In the above embodiment, the process of solving γ is as follows: first, the sample is observed under SEM, and a particle with a D50 value of particle size is completely photographed under SEM at a suitable magnification. In the photographed positive electrode particles, at least 10 flaky particles are selected for characterization calculation, then a horizontal axis is set, and the counterclockwise orientation angle between the length direction of the selected flaky particles for calculation and the set horizontal axis (the angle rotated by the horizontal axis counterclockwise to coincide with the length direction of the flaky particle) is measured, and the measured counterclockwise orientation angle is taken as θi, i=1, 2, 3, …, 10, and the average value of the measured counterclockwise orientation angle is taken as θ, then the set horizontal axis is rotated in the range of [-π / 2, π / 2], and the maximum value of γ is calculated, and the maximum value of γ can represent the consistency of the orientation distribution of the flaky particles of the positive electrode material, when γ takes the maximum value, the angle of rotation of the set horizontal axis is δ, in this embodiment, through iterative calculation, when δ=-0.2 radian is satisfied, γ takes the maximum value 0.80. The closer the value of γ is to 1, the higher the orientation distribution consistency of the flaky particles is. Figure 1 In this embodiment, 12 flaky particles are selected for calculation, and the counterclockwise orientation angle between the length direction and the set horizontal axis is measured to be 28°, 61°, 64°, 71°, 78°, 97°, 98°, 110°, 128°, 132°, 144° and 162° respectively by using a protractor, then the set horizontal axis is rotated in the range of [-π / 2, π / 2], and the maximum value of γ is calculated, and the maximum value of γ can represent the consistency of the orientation distribution of the flaky particles of the positive electrode material, when γ takes the maximum value, the angle of rotation of the set horizontal axis is δ, in this embodiment, through iterative calculation, when δ=-0.2 radian is satisfied, γ takes the maximum value 0.80. The closer the value of γ is to 1, the higher the orientation distribution consistency of the flaky particles is. The maximum value of γ can represent the consistency of the orientation distribution of the flaky particles of the positive electrode material, when γ takes the maximum value, the angle of rotation of the set horizontal axis is δ, in this embodiment, through iterative calculation, when δ=-0.2 radian is satisfied, γ takes the maximum value 0.80. The closer the value of γ is to 1, the higher the orientation distribution consistency of the flaky particles is.

[0044] It should be understood that the smaller γ is, the more staggered the flaky particles are (the greater the difference between the counterclockwise orientation angles between the length directions of the flaky particles and the set horizontal axis is); the closer γ is to 1, the more obvious the orientation consistency of the flaky particles is (the smaller the difference between the counterclockwise orientation angles between the length directions of the flaky particles and the set horizontal axis is), and γ=1, which is equivalent to the state of parallel stacking of the flaky particles, belongs to the most ordered state.

[0045] It should be understood that the calculation method of γ is as follows: θi is measured, and then the set horizontal axis is rotated in the range of [-π / 2, π / 2], and the maximum value of γ is calculated. i , and δ is a periodic function of only one variable, and each time δ takes a value, it corresponds to a γ, and the periodic function can take a maximum value in the range of [-π / 2, π / 2].

[0046] Another embodiment of a positive electrode material, the positive electrode material comprises a plurality of flaky particles, and the positive electrode material satisfies the following relationship:

[0047] 0.70≤Ψ≤1.12, wherein Ψ=[2-α*β / 0.85+γ] / 2;

[0048] wherein α=(D v90 -D v10 ) / D v50 , Dv 90 , Dv 10 and Dv 50respectively are particle size distribution parameters of the positive electrode material, β is Dv 50 an average value of a ratio of a long axis length to a short axis length of the spheroid in the particle size distribution range, n is D v50 a number of the flaky particles selected for calculation on the spheroid in the particle size distribution range, n≥10; θ i is an included angle between a length direction of the i-th selected flaky particle and a set horizontal axis in a counterclockwise direction, δ is a rotation angle relative to the set horizontal axis when the set horizontal axis is rotated to make γ maximum in the range of [-π / 2, π / 2].

[0049] In the above embodiments, Ψ is a uniform regularity parameter of the positive electrode material, which reflects the joint action of α, β and γ, that is, the three elements of particle size distribution, spheroid morphology and orientation consistency of the flaky particles are comprehensively considered, when the above three elements are all better, the positive electrode material has better specific surface area, tap density, processing performance and electrical performance. The higher the value of Ψ is in the limited range, the more advantageous the comprehensive performance of the corresponding material is.

[0050] The chemical general formula of the positive electrode material in the above embodiments is: Na x (Ni a Fe b M c Mn 1-a-b-c )O2, wherein M is selected from one or two or more elements of Li, Mg, Ca, Cu, Al, Co, Zr, Ti, Sn, Sb, Ta and W, 0.70≤x≤1.05, 0.1≤a≤0.6, 0.2≤b≤0.35, 0≤c≤0.15, in the structure of the above chemical general formula, the content of M metal is low, which is a doped metal, therefore, the sodium ion positive electrode material of the application is mainly a nickel-iron-manganese-based sodium ion positive electrode material.

[0051] Referring to Figure 1 , the sodium ion positive electrode material of the application includes spheroids formed by agglomeration of a plurality of flaky particles with uniform size, preferably, the length of the flaky particle is 0.5 μm to 2 μm, which can be specifically 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm or 2.0 μm. It can be seen that the length distribution range of the flaky particle of the application is relatively narrow, which indicates that the size of the flaky particle is relatively close, and the spheroid with uniform size and regular shape can be obtained from the flaky particle with uniform size.

[0052] The thickness of the flaky particles is 50 nm to 200 nm, and can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, or 200 nm. Since the flaky particles are formed by layer-by-layer deposition, the earlier the flaky particles are formed, the thicker the thickness can be.

[0053] The long axis of the spheroid is 5 μm to 15 μm, and can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or 16 μm, and the short axis of the spheroid is 5 μm to 15 μm, and can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or 16 μm. The size of the spheroid in the present scheme is related to the size of the flaky particles and the deposition time, and the longer the deposition time, the larger the volume of the spheroid grown.

[0054] The particle size distribution concentration α of the sodium ion positive electrode material is in the range of 0.65≤α≤1.25, and specifically, α can be 0.65, 0.7, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, or 1.25, and the sphericity regularity β of the sodium ion positive electrode material is in the range of 1≤β≤1.1, and specifically, β can be 1, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, or 1.1. The positive electrode material of the present application has a very narrow particle size distribution compared to the prior art, and therefore, the tap density can be significantly improved.

[0055] In some embodiments, the specific surface area of the sodium ion positive electrode material is 0.1 m 2 / g to 10 m 2 / g. Specifically, the specific surface area of the sodium ion positive electrode material can be 0.1 m 2 / g, 0.3 m 2 / g, 0.5 m 2 / g, 0.7 m 2 / g, 1 m 2 / g, 2 m 2 / g, 3 m 2 / g, 4 m 2 / g, 5 m 2 / g, 6 m 2 / g, 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, or 10 m 2 / g.

[0056] In preferred embodiments, the specific surface area of the sodium-ion positive electrode material is 0.2 m 2 / g to 2 m 2 / g. Specifically, the specific surface area of the sodium-ion positive electrode material is preferably 0.2 m 2 / g, 0.3 m 2 / g, 0.4 m 2 / g, 0.5 m 2 / g, 0.6 m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g, 1.0 m 2 / g, 1.2 m 2 / g, 1.4 m 2 / g, 1.6 m 2 / g, 1.8 m 2 / g or 2 m 2 / g.

[0057] In some embodiments, the tap density of the sodium-ion positive electrode material is 1.5 g / cm 3 to 2.5 g / cm 3 . Specifically, the tap density of the sodium-ion positive electrode material can be 1.5 g / cm 3 , 1.6 g / cm 3 , 1.7 g / cm 3 , 1.8 g / cm 3 , 1.9 g / cm 3 , 2.0 g / cm 3 , 2.1 g / cm 3 , 2.2 g / cm 3 , 2.3 g / cm 3 , 2.4 g / cm 3 or 2.5 g / cm 3 .

[0058] In some embodiments, the Dv 50 50 particle size of the sodium-ion positive electrode material is 3 μm to 15 μm. Specifically, the Dv 50 50 particle size of the sodium-ion positive electrode material can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm.

[0059] In preferred embodiments, the Dv 50 50 particle size of the sodium-ion positive electrode material is 6 μm to 12 μm.

[0060] In some embodiments, the Dv 90The particle size is 9-20 μm, preferably 6-11 μm. Specifically, the Dv50 of the sodium-ion positive electrode material is 6-11 μm. 50 The particle size can be 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or 11 μm.

[0061] In some embodiments, the Dv50 of the sodium-ion positive electrode material is 2-5 μm. 10 The particle size is 2-5 μm. As can be seen, the positive electrode material of the application has a small amount of smaller spherical particles.

[0062] In preferred embodiments, the Dv50 of the sodium-ion positive electrode material is 3-5 μm. 10 The particle size is 3-5 μm.

[0063] The preparation method of the above-mentioned sodium-ion positive electrode material of another embodiment, the chemical formula of the sodium-ion positive electrode material is: Na x (Ni a Fe b M c Mn 1-a-b-c )O2, wherein M comprises at least one of Li, Mg, Ca, Cu, Al, Co, Zr, Ti, Sn, Sb, Ta and W, 0.70≤x≤1.05, 0.1≤a≤0.6, 0.2≤b≤0.35, 0≤c≤0.15; comprising the following steps:

[0064] S1: preparing a first solution, the first solution comprising a soluble nickel salt, a soluble divalent iron salt and a soluble manganese salt, the element molar amount of nickel, iron and manganese in the first solution satisfying the chemical formula of the sodium-ion positive electrode material.

[0065] In the present embodiment, the purpose of preparing the first solution is to enable the mixed salt to be simultaneously added to the reaction container, to uniformly generate the co-precipitate of nickel hydroxide, iron hydroxide and manganese hydroxide, and at the same time, to avoid increasing the number of nickel-iron-manganese-based precursor production line related equipment.

[0066] The first solution of the present embodiment comprises divalent nickel ions, divalent iron ions and divalent manganese ions. Since the divalent iron ions are easily oxidized to form trivalent iron ions, the trivalent iron ions can cause the nickel-iron-manganese-based precursor to not grow much during the co-precipitation reaction, resulting in a wide particle size distribution of the nickel-iron-manganese-based precursor, and also resulting in a wide particle size distribution of the sintered sodium-ion positive electrode material.

[0067] In preferred embodiments, the first solution is protected by a non-oxygen protective atmosphere to avoid the oxidation of divalent iron ions to form trivalent iron ions.

[0068] In some embodiments, the soluble nickel salt comprises at least one of nickel acetate, nickel chloride, nickel nitrate and nickel sulfate.

[0069] In some embodiments, the soluble divalent iron salt includes at least one of ferrous chloride, ferrous sulfate, ferrous nitrate, and ferrous carbonate.

[0070] In some embodiments, the soluble manganese salt includes at least one of manganese sulfate, manganese chloride, and manganese nitrate.

[0071] In some embodiments, the total molar concentration of the soluble nickel salt, the soluble divalent iron salt, and the soluble manganese salt in the first solution is 2 mol / L to 2.4 mol / L. Specifically, the total molar concentration of the soluble nickel salt, the soluble divalent iron salt, and the soluble manganese salt can be 2 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, or 2.4 mol / L. Controlling the concentration of the solution can control the growth rate and quality of the precipitated crystals.

[0072] S2: preparing a second solution, the second solution including a basic precipitant and a soluble carbonate salt.

[0073] In the present embodiment, the basic precipitant is used to provide hydroxide ions, so that the divalent nickel ions, the divalent iron ions, and the divalent manganese ions respectively generate hydroxide co-precipitates (i.e., nickel-iron-manganese-based precursor precipitates) with the hydroxide ions. The soluble carbonate salt is used to provide doped carbonate ions for the crystal lattice of the hydroxide co-precipitate. The doping of the carbonate ions can effectively improve the morphology and agglomeration mode of the hydroxide co-precipitate (i.e., the nickel-iron-manganese-based precursor precipitate). The carbonate ions occupy a large space in the crystal lattice of the hydroxide co-precipitate, so that the hydroxide co-precipitate generates a certain amount of loose voids, which is conducive to the body phase diffusion of sodium ions in the subsequent mixed sodium carbonate sintering process.

[0074] In the present embodiment, the purpose of preparing the second solution including the soluble carbonate salt and the basic precipitant is to make the soluble carbonate salt and the basic precipitant co-precipitate at the same time, so that the carbonate ions are uniformly doped in the crystal lattice of the hydroxide co-precipitate.

[0075] In some embodiments, the total molar concentration of the basic precipitant and the soluble carbonate salt in the second solution is 4 mol / L to 6 mol / L. Specifically, the total molar concentration of the basic precipitant and the soluble carbonate salt can be 4 mol / L, 5 mol / L, or 6 mol / L. The concentration of the basic precipitant also affects the growth rate and quality of the precipitated crystals.

[0076] In some embodiments, the soluble carbonate in the second solution has a molar amount of 1% to 10% of the total molar amount of the basic precipitant and the soluble carbonate. Specifically, the soluble carbonate can have a molar amount of 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% of the total molar amount of the basic precipitant and the soluble carbonate. The doping of the soluble carbonate can change the growth direction of the deposited crystals. During the sintering step, the carbonate is volatilized in the form of carbon dioxide, forming voids, thereby forming the spheroids formed by the agglomeration of the flaky particles layer by layer.

[0077] In some embodiments, the basic precipitant includes at least one of sodium hydroxide and potassium hydroxide.

[0078] In some embodiments, the soluble carbonate includes at least one of sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate.

[0079] S3: preparing a third solution including ammonia and a reducing agent.

[0080] In the present embodiment, the ammonia is used as a complexing agent to complex with the divalent nickel ions, divalent iron ions, and divalent manganese ions to form flocculent metal complexes. The reducing agent is used to inhibit the oxidation of the divalent iron ions into trivalent iron ions. After the trivalent iron ions are formed, small-size particles are easily formed, and the growth of the crystals is inhibited. The small-size particles are attached to the flaky particles, which easily leads to irregular shapes of the flaky particles. Avoiding the formation of the trivalent iron ions can make the size of the flaky particles on the spheroids more uniform.

[0081] In some embodiments, the concentration of the ammonia in the third solution is 2 g / L to 6 g / L. Specifically, the concentration of the ammonia in the third solution can be 2 g / L, 3 g / L, 4 g / L, 5 g / L, or 6 g / L. The concentration of the ammonia also affects the growth speed and quality of the precipitated crystals.

[0082] In some embodiments, the concentration of the reducing agent in the third solution is 0.2 mL / L to 5 mL / L. Specifically, the concentration of the reducing agent in the third solution can be 0.2 mL / L, 0.5 mL / L, 1 mL / L, 1.5 mL / L, 2 mL / L, 2.5 mL / L, 3 mL / L, 3.5 mL / L, 4 mL / L, 4.5 mL / L, or 5 mL / L.

[0083] In some embodiments, the reducing agent includes at least one of hydrazine hydrate, sodium sulfite, and sodium borohydride.

[0084] S4: mixing the reaction solution after the mixing reaction of the first solution and the third solution with the second solution under a protective atmosphere to obtain a nickel-iron-manganese-based precursor precipitate.

[0085] It can be understood that, under the condition of continuously introducing the protective atmosphere, the reaction solution after the mixing reaction of the first solution and the third solution is mixed with the second solution to obtain the nickel-iron-manganese-based precursor precipitate.

[0086] Specifically, a non-oxygen protective atmosphere is continuously introduced into a reaction container, the third solution is injected into the reaction container, the first solution is injected into the reaction container, the first solution is mixed with the third solution to obtain a reaction solution, the reaction solution is continuously stirred, the second solution is injected into the reaction solution, the pH of the reaction solution is maintained at 10.5-12, specifically can be 10.5, 11, 11.5 or 12, a coprecipitation reaction occurs, and a nickel-iron-manganese-based precursor precipitate is obtained.

[0087] In the present embodiment, the coprecipitation reaction is carried out under the condition of continuously introducing a non-oxygen protective atmosphere, so as to avoid the oxidation of ferrous ions into ferric ions during the coprecipitation reaction, and avoid the nickel-iron-manganese-based precursor precipitate from growing too small, which affects the particle size distribution width of the nickel-iron-manganese-based precursor precipitate. In the present application, the oxidation of ferrous ions is inhibited by the non-oxygen protective atmosphere and the reducing agent, so as to obtain flaky particles with uniform size, thereby obtaining uniform spherical particles formed by the agglomeration of flaky particles with uniform size.

[0088] In the present embodiment, the second solution is used to adjust the pH value of the coprecipitation reaction, and the injection amount and injection speed of the second solution can be adjusted according to the pH value of the reaction solution. The present application maintains the pH value of the coprecipitation reaction process in the range of 10.5-12, so as to ensure the consistency of the reaction conditions during the whole coprecipitation reaction process, thereby ensuring the consistency of the morphology of the coprecipitation product, i.e. obtaining flaky particles with uniform size.

[0089] In the present embodiment, the coprecipitation reaction starts as soon as the third solution and the first solution are mixed, and the speed of the coprecipitation reaction, as well as the morphology and size of the nickel-iron-manganese-based precursor product, can be controlled by controlling the temperature, stirring speed, concentration of each reactant, relative injection speed of the first solution and the third solution, and other parameters of the reaction solution.

[0090] In the present embodiment, the first solution and the third solution can be injected into the reaction container at the same time, or the third solution can be injected into the reaction container first, and then the first solution can be gradually injected under stirring conditions, or the first solution can be injected into the reaction container first, and then the third solution can be gradually injected under stirring conditions.

[0091] In some embodiments, the temperature of the reaction solution is in the range of 50-60°C. Specifically, the temperature of the reaction solution can be 50°C, 55°C or 60°C.

[0092] In some embodiments, the stirring rate of the reaction solution is 400 rpm to 900 rpm. Specifically, the stirring rate of the reaction solution can be 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, or 900 rpm.

[0093] In some embodiments, the particle size of the nickel-iron-manganese-based precursor precipitate is 5 μm to 11 μm, so as to control the particle size range of the generated sodium-ion positive electrode material. Specifically, the particle size of the nickel-iron-manganese-based precursor precipitate can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or 11 μm.

[0094] In some embodiments, the third solution is first injected into the reaction container, and then the first solution is gradually injected into the reaction container, and the injection rate of the first solution satisfies that the reaction container is filled within 10 h to 15 h.

[0095] Preferably, the single-liquor-quantity of the first solution satisfies that the single-feeding time is less than 5 h, and after the single-liquor-quantity of the first solution is completely injected into the reaction container, the supernatant is settled and emptied, and the injection of the first solution, the second solution, and the third solution into the reaction container is repeated, and the co-precipitation reaction is repeatedly performed until the particle size of the nickel-iron-manganese-based precursor precipitate is 5 μm to 11 μm. This embodiment reduces the single-liquid injection time, which can effectively prevent the oxidation of divalent iron ions and prevent a large amount of trivalent iron ions from appearing in the co-precipitation process, thereby preventing the problem that the precursor does not grow large and the tap density is low.

[0096] In some embodiments, the gas of the protective atmosphere includes at least one of nitrogen and an inert gas.

[0097] S5: mixing the nickel-iron-manganese-based precursor with a sodium source to obtain a mixture;

[0098] In some embodiments, the sodium source includes sodium carbonate.

[0099] In some embodiments, the step of mixing the nickel-iron-manganese-based precursor with the sodium source further includes adding a dopant, and the dopant includes M metal oxide powder; M includes at least one of Li, Mg, Ca, Cu, Al, Co, Zr, Ti, Sn, Sb, Ta, and W.

[0100] S6: sintering the mixture to obtain a positive electrode material.

[0101] The positive electrode material includes a plurality of flaky particles, and the positive electrode material satisfies the following relationship:

[0102] 0.70≤Ψ≤1.12, wherein Ψ=[2-α*β / 0.85+γ] / 2;

[0103] wherein α=(D v90 -D v10) / D v50 , Dv 90 , Dv 10 and Dv 50 are particle size distribution parameters of the positive electrode material, β is the average value of the ratio of the long axis length to the short axis length of the spheroid in the particle size distribution range, 50 n is D v50 the number of the flaky particles selected for calculation on the spheroid in the particle size distribution range, n≥10; θ i is the included angle between the length direction of the i-th flaky particle selected and the set horizontal axis in the counterclockwise direction, and δ is the rotation angle of the set horizontal axis when γ takes the maximum value in the range of [-π / 2, π / 2].

[0104] In some embodiments, the oxygen content in the sintering atmosphere is greater than 21%. Specifically, it can be 21%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%.

[0105] In some embodiments, the continuous flow rate of the sintering atmosphere is 5L / H-50L / H. Specifically, the continuous flow rate of the sintering atmosphere can be 5L / H, 10L / H, 15L / H, 20L / H, 25L / H, 30L / H, 35L / H, 40L / H, 45L / H or 50L / H.

[0106] In some embodiments, the sintering pressure is 0.1MPa-0.5MPa. Specifically, the sintering pressure can be 0.1MPa, 0.2MPa, 0.3MPa, 0.4MPa or 0.5MPa.

[0107] In some embodiments, the sintering temperature is 700℃-950℃. Specifically, the sintering temperature can be 700℃, 750℃, 800℃, 850℃, 900℃ or 950℃.

[0108] In some embodiments, the sintering time is 5h-20h. Specifically, the sintering time can be 5h, 10h, 15h or 20h, preferably 10h-15h.

[0109] The following are specific embodiments.

[0110] Embodiment 1

[0111] 1) Take NiSO4·6H2O, FeSO4·7H2O and MnSO4·H2O as raw materials, and prepare a solution with a mass ratio of Ni:Fe:Mn=1:1:1 according to the formula of NiSO4·6H2O:FeSO4·7H2O:MnSO4·H2O=1:1:1. 0.25 Fe 0.25 Mn 0.5 ​SO4configuration 2 mol / L of the first solution 4L; preparation of the second solution containing 4 mol / L NaOH and 0.2 mol / L sodium carbonate; preparation of the third solution containing 5 g / L ammonia and 0.2 mL / L hydrazine 4L;

[0112] 2) Under the protection of continuous nitrogen, 4L of the third solution was injected into the reaction vessel, 4L of the first solution was gradually injected into the reaction vessel at an injection rate of 15 mL / min, and the second solution was injected into the reaction vessel at a stirring rate of 800 rpm and 50°C to maintain the pH of the reaction solution between 11 and 12, and the co-precipitation reaction was carried out. After 4L of the first solution was injected, the supernatant was obtained by standing, and the supernatant was emptied. Steps 1) and 2) were repeated until the particle size Dv 50 to reach the target value 5.6 μm;

[0113] 3) After the nickel-iron-manganese-based precursor precipitate obtained in step 2) was washed and dried, Na2CO3 was prepared according to x=0.75, mixed, and placed in a muffle furnace under an air atmosphere with a continuous flow rate of 10 L / min at 850°C for 12 h, and finally a sodium ion battery electrode material was obtained.

[0114] Example 2

[0115] 1) NiSO4·6H20, FeSO4·7H20 and MnSO4·H20 were used as raw materials, and the molar ratio of Ni 0.35 Fe 0.25 Mn 0.4 SO4configuration 2 mol / L of the first solution 4L; preparation of the second solution containing 4 mol / L NaOH and 0.2 mol / L sodium carbonate; preparation of the third solution containing 5 g / L ammonia and 0.2 mL / L hydrazine 4L;

[0116] 2) Under the protection of continuous nitrogen, 4L of the third solution was injected into the reaction vessel, 4L of the first solution was gradually injected into the reaction vessel at an injection rate of 15 mL / min, and the second solution was injected into the reaction vessel at a stirring rate of 800 rpm and 50°C to maintain the pH of the reaction solution between 11 and 12, and the co-precipitation reaction was carried out. After 4L of the first solution was injected, the supernatant was obtained by standing, and the supernatant was emptied. Steps 1) and 2) were repeated until the particle size Dv 50 to reach the target value 10 μm;

[0117] 3) After the nickel-iron-manganese-based precursor precipitate obtained in step 2) was washed and dried, Na2CO3 was prepared according to x=0.85, mixed, and placed in a muffle furnace under an air atmosphere with a continuous flow rate of 20 L / min at 870°C for 12 h, and finally a sodium ion battery electrode material was obtained.

[0118] Example 3

[0119] 1) A first solution of 4L was prepared using NiSO4·6H2O, FeSO4·7H2O, CuSO4·5H2O and MnSO4·H2O as raw materials, according to the proportion of Ni 0.25 Cu 0.1 Fe 0.25 Mn 0.4 SO4, and a second solution was prepared containing 3.864 mol / L NaOH and 0.336 mol / L sodium carbonate, and a third solution of 4L was prepared containing 2 g / L ammonia water and 0.2 mL / L hydrazine hydrate;

[0120] 2) Under the protection of continuous nitrogen, 4L of the third solution was injected into the reaction container, and 4L of the first solution was gradually injected into the reaction container at an injection rate of 15 mL / min. The second solution was injected into the reaction container at a stirring rate of 800 rpm and 50°C to maintain the pH of the reaction solution between 11 and 12, and the co-precipitation reaction was carried out. After the injection of 4L of the first solution was completed, the supernatant was obtained by standing, and the supernatant was emptied. Steps 1) and 2) were repeated until the particle size Dv 50 of the nickel-iron-manganese-based precursor reached the target value of 9μm;

[0121] 3) After the nickel-iron-manganese-based precursor obtained in step 2) was washed and dried, Na2CO3 was prepared according to the proportion of x=1.0, mixed, and placed in a muffle furnace. The final sodium-ion battery electrode material was obtained by sintering at 880°C for 12h under an air atmosphere with a continuous flow rate of 30L / min.

[0122] Example 4

[0123] 1) A first solution of 4L was prepared using NiSO4·6H2O, FeSO4·7H2O and MnSO4·H2O as raw materials, according to the proportion of Ni 0.6 Fe 0.2 Mn 0.2 SO4, and a second solution was prepared containing 4.116 mol / L NaOH and 0.084 mol / L sodium carbonate, and a third solution of 4L was prepared containing 6 g / L ammonia water and 0.2 mL / L hydrazine hydrate;

[0124] 2) Under the protection of continuous nitrogen, 4L of the third solution was injected into the reaction container, and 4L of the first solution was gradually injected into the reaction container at an injection rate of 15 mL / min. The second solution was injected into the reaction container at a stirring rate of 800 rpm and 50°C to maintain the pH of the reaction solution between 11 and 12, and the co-precipitation reaction was carried out. After the injection of 4L of the first solution was completed, the supernatant was obtained by standing, and the supernatant was emptied. Steps 1) and 2) were repeated until the particle size Dv 50 of the nickel-iron-manganese-based precursor reached the target value of 10μm;

[0125] 3) The nickel-iron-manganese-based precursor obtained in step 2) is washed and dried, Na2CO3 is added in a proportion of x = 1.03, and 3wt% Al2O3 is added, and then mixed, and then placed in a muffle furnace and sintered at 880°C for 12h under an air atmosphere with a continuous flow rate of 40L / min, to obtain a sodium-ion battery electrode material.

[0126] Comparative Example 1

[0127] Comparative Example 1 differs from Example 1 only in that the second solution does not include sodium carbonate, and the rest is the same.

[0128] Comparative Example 2

[0129] Comparative Example 2 differs from Example 1 only in that the third solution does not include hydrazine hydrate, and the rest is the same.

[0130] Comparative Example 3

[0131] Comparative Example 3 differs from Example 1 only in that the second solution does not include sodium carbonate, and the third solution does not include hydrazine hydrate, and the rest is the same.

[0132] Comparative Example 4

[0133] Comparative Example 4 is prepared using the existing preparation method, and the specific preparation process is as follows: nickel oxide, iron oxide, manganese oxide, copper oxide and sodium carbonate are mixed in a stoichiometric ratio of NaNi 0.25 Cu 0.1 Fe 0.25 Mn 0.4 O2 to form a precursor; the precursor is uniformly mixed by ball milling to obtain a precursor powder. The precursor powder is placed in a muffle furnace and heat treated at 900°C for 15h under a flow rate of 15L / min of air. The heat-treated precursor powder is ground to obtain the layered oxide material.

[0134] The sodium-ion positive electrode material prepared in each of the above examples and comparative examples is subjected to performance testing.

[0135] The morphology of the prepared sodium-ion positive electrode material is observed and characterized by SEM scanning images, and the results are shown in Figure 1 and Figure 2 .

[0136] The length and thickness of the flaky particles, and the long axis and short axis of the spherical particles are directly calibrated after SEM testing, and the results are shown in Table 1.

[0137] The Dv 90 , Dv 50 , and Dv 10Particle size distribution, light shielding rate 60-80%, refractive index 2.0, dispersion medium is water, the results are shown in Table 1.

[0138] The specific surface area was tested by a tester TriStar3030, and the results are shown in Table 2.

[0139] The tap density of the powder was tested by a tap density tester DAT-6-220-50, and the results are shown in Table 2.

[0140] The prepared positive electrode material was electrochemically evaluated by a button half cell, and the specific method was as follows: sodium ion positive electrode material, conductive carbon black Super P and polyvinylidene fluoride (PVDF) were weighed according to a mass ratio of 90:5:5, N-methyl pyrrolidone (NMP) was added according to a solid content of 50%, a high-speed dispersing machine was used to adjust the slurry into a viscous paste, a doctor blade was used to uniformly coat the paste on an aluminum foil, and the aluminum foil was baked in a 100℃ oven to dry, and a dry positive electrode sheet was obtained.

[0141] The experimental process of the positive electrode sheet compaction was as follows: the dry positive electrode sheet was rolled at a rolling pressure of 1-5T, the positive electrode sheet was folded three times after rolling, and the fold was observed to be opaque. Under the above conditions, the positive electrode sheet was rolled at the maximum pressure that could be tolerated, the thickness of the positive electrode sheet was tested, and the compaction density was calculated as the surface density / the thickness of the material, wherein the surface density was the total mass of the sodium ion positive electrode material, conductive carbon black Super P and polyvinylidene fluoride (PVDF) contained in the unit area of the positive electrode sheet.

[0142] The rolled positive electrode sheet was cut into a positive electrode sheet with a diameter of 14mm. A sodium sheet with a diameter of 16mm was used as a negative electrode sheet, a ceramic fiber membrane was used as a separator, and a solution of NaPF6 with a concentration of 1mol / L in carbonate (diethyl carbonate (DEC) / ethylene carbonate (EC) with a volume ratio of 1:1) was used as an electrolyte, and the button half cell was assembled in an argon-filled glove box.

[0143] The button half cell prepared above was subjected to electrical performance testing on an AUTOLAB PGSTAT 302N type electrochemical workstation and a LAND CT3002A. The button cell was subjected to 1C=100mAh / g, and the voltage test interval was 2.0-4.1V, and the results are shown in Table 2.

[0144] Table 1: Morphology characterization of the sodium ion positive electrode material prepared in each example and comparative example

[0145]

[0146] Table 2: Performance characterization of the sodium ion positive electrode material prepared in each example and comparative example

[0147]

[0148] Comparing Examples 1-4 with Comparative Example 4, the latter uses a grinding and sintering preparation method of the prior art, which is completely different from the co-precipitation and sintering method of the present application. First, referring to Table 1, it can be seen that: 1) the parameter a, which characterizes the particle size distribution of the spherical particles of the positive electrode material, ranges from 0.71 to 0.95 for Examples 1-4, which is closer to 1 than 1.57 for Comparative Example 4, indicating that the particle size distribution of the positive electrode material prepared by the present application is narrower and the particle size distribution is more uniform; 2) the parameter β, which characterizes the regularity of the spherical shape of the spherical particles of the positive electrode material, ranges from 1.02 to 1.05 for Examples 1-4, which is significantly closer to 1 than 2.02 for Comparative Example 4, indicating that the closer to 1, the closer to a sphere. It can be seen that the positive electrode material obtained by Examples 1-4 is a spherical or spherical-like particle with a regular shape and uniform distribution. The data in Table 1 is consistent with the results of SEM and TEM. Figure 1 and Figure 2 are SEM images of the positive electrode materials prepared by Examples 1 and Comparative Example 4, respectively. It can be seen from the images that the positive electrode material obtained by the co-precipitation preparation method of the present application comprises spherical particles formed by agglomeration of a plurality of sheet-shaped particles with uniform size, while the positive electrode material prepared by Comparative Example 4 is a particle with a smooth surface and irregular shape.

[0149] Second, referring to Table 1, it can be seen that: 1) the parameter a, which characterizes the particle size distribution of the spherical particles of the positive electrode material, ranges from 0.71 to 0.95 for Examples 1-4, which is closer to 1 than 1.57 for Comparative Example 4, indicating that the particle size distribution of the positive electrode material prepared by the present application is narrower and the particle size distribution is more uniform; 2) the parameter β, which characterizes the regularity of the spherical shape of the spherical particles of the positive electrode material, ranges from 1.02 to 1.05 for Examples 1-4, which is significantly closer to 1 than 2.02 for Comparative Example 4, indicating that the closer to 1, the closer to a sphere. It can be seen that the positive electrode material obtained by Examples 1-4 is a spherical or spherical-like particle with a regular shape and uniform distribution. The data in Table 1 is consistent with the results of SEM and TEM. Figure 1 and Figure 2 are SEM images of the positive electrode materials prepared by Examples 1 and Comparative Example 4, respectively. It can be seen from the images that the positive electrode material obtained by the co-precipitation preparation method of the present application comprises spherical particles formed by agglomeration of a plurality of sheet-shaped particles with uniform size, while the positive electrode material prepared by Comparative Example 4 is a particle with a smooth surface and irregular shape.

[0150] Third, referring to Table 2, it can be seen that: 1) the specific surface area of the positive electrode material prepared by Examples 1-4 is 0.4-0.9 m 2 / g, while the specific surface area of Comparative Example 4 is 3.5 m 2 / g. In the technical field, the optimal range of the specific surface area of the positive electrode material is <1 m 2 / g. It can be seen that the co-precipitation method of the present application can make the specific surface area of the positive electrode material reach the optimal level in the field; 2) the tap density of the positive electrode material prepared by Examples 1-4 is 2.0-2.3 g / cm 3 , which is significantly better than 1.8 g / cm 3 for Comparative Example 4; 3) the electrode sheet compactness of the positive electrode material prepared by Examples 1-4 is 3.1-3.4 g / cm 3 , which is significantly better than 2.6 g / cm 3 for Comparative Example 4. In the technical field, the optimal range of the electrode sheet compactness parameter of the positive electrode material is >3 g / cm 3 , and the ideal value is 3.6-3.8 g / cm 3 . It can be seen that the co-precipitation method of the present application can make the electrode sheet compactness parameter of the positive electrode material reach the optimal level in the field; 4) the positive electrode material of Comparative Example 4 is the same as that of Example 3, both of which are NaNi 0.25 Cu 0.1Fe 0.25 Mn 0.4 O2, it can be seen from Table 2 that the capacity retention of the positive electrode material of Example 3 at 0.1C, 1C and 50 cycles is better than that of Comparative Example 4. In summary, the positive electrode material prepared by the present application has more excellent performance.

[0151] Comparing Example 1 with Comparative Example 1, Comparative Example 1 also adopts the same coprecipitation method as Example 1, the only difference is that sodium carbonate is not used in the preparation process of Comparative Example 1. The role of sodium carbonate is that carbonate ions are uniformly doped in the coprecipitate crystal lattice during the coprecipitation process, which improves the morphology and agglomeration mode of the hydroxide coprecipitate, reduces the nucleation rate of the hydroxide, increases the pore volume of the precursor, facilitates the complete diffusion of sodium ions during the sintering process, and obtains a sodium ion positive electrode with high tap density. First, referring to Table 1, compared with Comparative Example 1, the primary particles of Example 1 are longer and thicker, which can increase the orientation order of the primary particles and increase the value of γ. Then, referring to Table 2, it can be seen from Table 2 that the tap density of the material with the same composition is improved by adding sodium carbonate, and the positive electrode material has more excellent specific surface area, tap density, electrode compaction density and electrical performance.

[0152] Comparing Example 1 with Comparative Example 2, Comparative Example 2 also adopts the same coprecipitation method as Example 1, the only difference is that a reducing agent is not used in the preparation process of Comparative Example 2 to inhibit the oxidation of Fe 2+ , which can prevent the generation of too much small particle material and prevent the Dv 10 and Dv 90 gap from being too large. First, referring to Table 1, the value of α of the spheroid of Comparative Example 2 is higher, indicating that the size distribution between the particles is not uniform, then, referring to Table 2, compared with Comparative Example 2, the positive electrode material prepared by Example 1 has more excellent specific surface area, tap density, electrode compaction and electrical performance.

[0153] Comparing Example 1 with Comparative Example 3, Comparative Example 3 also adopts the same coprecipitation method as Example 1, the only difference is that a reducing agent is not used in the preparation process of Comparative Example 3 to inhibit the oxidation of Fe 2+ , and sodium carbonate is not used. First, referring to Table 1, the particle size distribution α and sphericity β of Comparative Example 3 are both poor, and referring to Table 2, the performance of the material of Comparative Example 3 is also poorer.

[0154] The above-described examples only express several embodiments of the present application, which are described in more detail and in detail, but should not be construed as limiting the scope of the application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A positive electrode material, characterized by, The chemical general formula of the positive electrode material is Na x (Ni a Fe b M c Mn 1-a-b-c )O2, wherein M is selected from at least one of Li, Mg, Ca, Cu, Al, Co, Zr, Ti, Sn, Sb, Ta and W, 0.70≤x≤1.05, 0.1≤a≤0.6, 0.2≤b≤0.35, 0≤c≤0.

15. The positive electrode material comprises a plurality of flaky particles, and an orientation distribution consistency parameter γ of the flaky particles ranges from 0.73 to less than 1, wherein ； n is D v50 The number of the flaky particles selected for calculation on the particle size of the positive electrode material, n≥10; θ i is the included angle between the length direction of the selected i-th flaky particle and the set horizontal axis in the counterclockwise direction, and δ is the rotation angle of the set horizontal axis when the rotation of the set horizontal axis makes γ take the maximum value in the range of [-π / 2, π / 2]. 0.65 < a < 1.25, where a = (D v90 - D v10 ) / D v50 ; D v90 , D v10 , and D v50 are the particle size distribution parameters of the positive electrode material, respectively. 1 < β < 1.1, where β is D v50 an average of the ratio of the long axis length to the short axis length of the positive electrode material in the particle size distribution range; The preparation method of the positive electrode material comprises the following steps: The reaction solution after mixing and reacting the first solution and the third solution is mixed with the second solution under a protective atmosphere to obtain a nickel-iron-manganese-based precursor precipitate; the first solution comprises a soluble nickel salt, a soluble divalent iron salt, and a soluble manganese salt; the second solution comprises an alkaline precipitant and a soluble carbonate salt; and the third solution comprises ammonia and a reducing agent; The nickel-iron-manganese-based precursor precipitate is mixed with a sodium source to obtain a mixture; The mixture is sintered to obtain the positive electrode material.

2. The positive electrode material of claim 1, wherein, The positive electrode material satisfies the following relationship: 0.70 < Ψ < 1.12, where Ψ = [2 - α β / 0.85 + γ] / 2; where α = (D v90 -D v10 ) / D v50 , D v90 , D v10 , and D v50 are the particle size distribution parameters of the positive electrode material, β is the average value of the ratio of the long axis length to the short axis length of the positive electrode material of D v50 particle size, ； n is D v50 The particle size of the positive electrode material is selected for the number of the flaky particles calculated, and n≥10; θ i is the angle between the length direction of the selected i-th flaky particle and the set horizontal axis in the counterclockwise direction, and δ is the rotation angle of the set horizontal axis when the rotation of the set horizontal axis makes γ take the maximum value in the range of [-π / 2, π / 2].

3. The positive electrode material according to any one of claims 1-2, characterized in that, At least one of the following features (1) to (5) is included: (1) The positive electrode material comprises a plurality of flaky particles; (2) The length of the flaky particles is 0.5 μm to 2 μm; (3) The thickness of the flaky particles is 50 nm to 200 nm; (4) The length of the long axis of the positive electrode material is 5 μm to 15 μm; (5) The length of the short axis of the positive electrode material is 5 μm to 15 μm.

4. The positive electrode material according to any one of claims 1 to 2, characterized by, At least one of the following features (1) to (5) is included: (1) the positive electrode material has a D v50 of 3 μm to 15 μm; (2) the positive electrode material has a D50 of 2 μm to 5 μm v10 2 μm to 5 μm; (3) the positive electrode material has a D v90 of 9 μm to 20 μm; (4) the specific surface area of the positive electrode material is 0.1 m 2 / g~10 m 2 / g; (5) the tap density of the positive electrode material is 1.5 g / cm 3 ~ 2.5 g / cm 3 .

5. The positive electrode material according to any one of claims 1 to 2, characterized by, At least one of the following features (1) to (2) is included: (1) the positive electrode material has a D v50 of 6 μm to 12 μm; (2) the specific surface area of the positive electrode material is 0.2 m 2 / g ~ 2 m 2 / g.

6. A method for producing the positive electrode material according to any one of claims 1 to 5, characterized by, The preparation method comprises the following steps: The reaction solution after mixing and reacting the first solution and the third solution is mixed with the second solution under a protective atmosphere to obtain a nickel-iron-manganese-based precursor precipitate; the first solution comprises a soluble nickel salt, a soluble divalent iron salt, and a soluble manganese salt; the second solution comprises an alkaline precipitant and a soluble carbonate salt; and the third solution comprises ammonia and a reducing agent; The nickel-iron-manganese-based precursor precipitate is mixed with a sodium source to obtain a mixture; The mixture is sintered to obtain the positive electrode material.

7. The method of claim 6, wherein the method further comprises a step of calcining the mixture at a temperature of 700-900°C for 5-20 hours. At least one of the following features (1) to (17) is satisfied: (1) In the first solution, the total molar concentration of the soluble nickel salt, the soluble divalent iron salt, and the soluble manganese salt is 2 mol / L to 2.4 mol / L; (2) In the second solution, the total molar concentration of the alkaline precipitant and the soluble carbonate salt is 4 mol / L to 6 mol / L; (3) In the second solution, the percentage of the molar amount of the soluble carbonate salt in the total molar amount of the alkaline precipitant and the soluble carbonate salt is 1% to 10%; (4) In the third solution, the concentration of the ammonia is 2 g / L to 6 g / L; (5) In the third solution, the concentration of the reducing agent is 0.2 mL / L to 5 mL / L; (6) The reaction solution is mixed with the second solution so that the pH of the reaction solution is 10.5 to 12; (7) The temperature of the reaction solution is 50°C to 60°C; (8) In the step of mixing the reaction solution with the second solution, the reaction solution is stirred at a stirring rate of 400 rpm to 900 rpm; (9) The soluble nickel salt comprises at least one of nickel acetate, nickel chloride, nickel nitrate, and nickel sulfate; (10) the soluble divalent iron salt comprises at least one of ferrous chloride, ferrous sulfate and ferrous nitrate; (11) the soluble manganese salt comprises at least one of manganese sulfate, manganese chloride and manganese nitrate; (12) the alkaline precipitant comprises at least one of sodium hydroxide and potassium hydroxide; (13) the soluble carbonate salt comprises at least one of sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate; (14) the reducing agent comprises at least one of hydrazine hydrate, sodium sulfite and sodium borohydride; (15) the gas of the protective atmosphere comprises at least one of nitrogen and inert gas; (16) the step of mixing the nickel-iron-manganese-based precursor precipitate with a sodium source further comprises adding a mixture of M metal oxides, wherein M comprises at least one of Li, Mg, Ca, Cu, Al, Co, Zr, Ti, Sn, Sb, Ta and W; (17) the sodium source comprises sodium carbonate.

8. The method of producing a cathode material according to claim 6 or 7, characterized in that, satisfy at least one of the following characteristics (1)-(3): (1) a single solution preparation amount of the first solution satisfies a single feeding time of less than 5 hours, after the single solution preparation amount of the first solution is completely injected into a reaction container, supernatant is obtained by standing, the supernatant is emptied, the first solution, the second solution and the third solution are repeatedly injected into the reaction container, and the co-precipitation reaction is repeatedly performed until the particle size of the nickel-iron-manganese-based precursor precipitate is 5-11 μm; (2) the oxygen content in a sintering atmosphere during the sintering process is greater than 21%; (3) the particle size of the nickel-iron-manganese-based precursor precipitate is 5-11 μm.

9. The method of claim 8, wherein the method further comprises a step of calcining the mixture at a temperature of 700-900°C for 1-10 hours. satisfy at least one of the following characteristics (1)-(4): (1) the continuous flow rate of the sintering atmosphere is 5-50 L / H; (2) the sintering pressure is 0.1-0.5 MPa; (3) the sintering temperature is 700-950°C; (4) the sintering time is 5-20 hours.

10. A sodium-ion battery, characterized in that, The positive electrode material prepared by the method of any one of claims 6-9 or the positive electrode material of any one of claims 1-5.

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