Positive electrode active material and preparation method thereof, positive electrode plate and sodium ion battery

Abstract

The invention discloses a positive active material and a preparation method thereof, a positive pole piece and a sodium ion battery. The positive electrode active material comprises an inner core and a carbon coating layer, wherein the carbon coating layer is positioned on at least part of the surface of the inner core; the equivalent particle size D of the positive electrode active material is 0.78-2.04 [mu] m, D = 6 / (S * T), S is the specific surface area of the positive electrode active material, and the unit is m < 2 > / g; t is the tap density of the positive electrode active material, and the unit is g / cm < 3 >. Therefore, the carbon coating layer is tightly attached to the inner core, the structural stability of the positive electrode active material is excellent, an effective conductive network can be formed through a small amount of carbon material, and the surface of the inner core is effectively protected.

Description

Technical Field

[0001] The present application relates to the field of sodium-ion batteries, and more specifically, to a positive electrode active material, a method for preparing the same, a positive electrode sheet, and a sodium-ion battery. Background Art

[0002] Due to its similar electrochemical principle to lithium-ion batteries, lower raw material cost, and similar industrialization process, sodium-ion batteries are widely regarded as strong competitors to lithium-ion batteries. Among the positive electrode active materials for sodium-ion batteries, layered transition metal oxides have received extensive attention due to their high theoretical specific capacity and simple synthesis process. However, current layered transition metal oxides still have problems to be solved in actual application and production.

[0003] It should be noted that the above statements are only used to provide background technical information related to the present application, and do not necessarily constitute prior art. Summary of the Invention

[0004] In a first aspect of the present application, a positive electrode active material is proposed, including: a core, and a carbon coating layer located on at least a part of the surface of the core; the equivalent particle size D of the positive electrode active material is 0.78 μm - 2.04 μm. D = 6 / (S × T), where S is the specific surface area of the positive electrode active material, in m 2 / g; T is the tapped density of the positive electrode active material, in g / cm 3 . Thus, the carbon coating layer and the core are closely attached, and the positive electrode active material has excellent structural stability. An effective conductive network can be formed with a small amount of carbon material to effectively protect the surface of the core.

[0005] In some embodiments, D is 0.85 μm - 1.82 μm. Thus, the carbon coating layer and the core are closely attached and the coating strength is moderate.

[0006] In some embodiments, S is 1.4 m 2 / g - 3.2 m 2 / g; optionally, 1.5 m 2 / g - 3.0 m 2 / g. Thus, the positive electrode active material has a smaller specific surface area and fewer side reactions with the electrolyte.

[0007] In some embodiments, T is 2.1 g / cm 3 - 2.4 g / cm 3 ; optionally, 2.20 g / cm 3 - 2.35 g / cm 3Thus, the tap density of the positive electrode active material is relatively high, and the internal voids of the positive electrode active material layer can be reduced.

[0008] In some embodiments, the carbon material in the carbon coating layer satisfies at least one of the following conditions: the particle size is less than or equal to 50 nm; the specific surface area is greater than or equal to 100 m 2 / g; the oil absorption value is greater than or equal to 250 mL / g. Thus, it helps the carbon coating layer to be evenly distributed on the surface of the core.

[0009] In some embodiments, the mass fraction of the carbon coating layer in the positive electrode active material is 0.5 wt% - 3.0 wt%; optionally, 0.8 wt% - 1.5 wt%. Thus, the positive electrode active material has both relatively good conductivity and a relatively high specific capacity.

[0010] In some embodiments, the carbon material in the carbon coating layer includes one or more of acetylene black, Super P, Ketjen black, conductive graphite, carbon nanotubes, and graphene. Thus, the carbon coating layer has relatively good conductivity.

[0011] In some embodiments, the tap density of the positive electrode active material under a pressure of 2 T is 3.2 g / cm 3 - 3.5 g / cm 3 ; optionally, 3.25 g / cm 3 - 3.40 g / cm 3 . Thus, it helps to improve the volume energy density of the battery using the positive electrode active material.

[0012] In some embodiments, the angle of repose of the positive electrode active material is less than or equal to 43°; optionally, less than or equal to 40°. Thus, it helps the positive electrode active material to be evenly coated on the surface of the positive electrode current collector and reduces the risk of cracking of the positive electrode active material layer.

[0013] In some embodiments, the oxygen defect concentration of the positive electrode active material is 2.5% - 4.5%. Thus, vacancies can be formed in the structure of the positive electrode active material, which is beneficial to the transport of sodium ions and can also relieve the structural stress change of the positive electrode active material during charge and discharge.

[0014] In some embodiments, the core satisfies the chemical formula: Na a (Ni 1-b-c-d Fe b Mn c M d )Q e O 2-f, where 0.95 ≤ a ≤ 1.10, 0.03 ≤ b ≤ 0.50, 0.03 ≤ c ≤ 0.50, 0 ≤ d ≤ 0.15, 0 ≤ e ≤ 0.10, 0 ≤ f ≤ 0.25; M includes one or more of V, Ta, Cr, La, Al, Ce, Y, Mg, Sr, Ba, Ra, Zr, Ca, Zn, B, W, Nb, Cd, Pb, Si, Mo, Co, Li, Ti, and Cu, and Q includes one or more of V, Ta, Cr, La, Al, Ce, Y, Mg, Sr, Ba, Ra, Zr, Ca, Zn, B, W, Nb, Cd, Pb, Si, Mo, F, P, Co, Li, Ti, and Cu. Thus, by doping with different elements, cathode active materials that meet different performance requirements can be obtained.

[0015] In a second aspect of the present application, the present application provides a method for preparing the aforementioned cathode active material, including: mixing a nickel source, an iron source, a manganese source, a complexing agent, and a precipitating agent to obtain a precursor slurry, and performing a drying treatment to obtain a precursor material; mixing the precursor material, a sodium source, and an M source, and performing a first sintering treatment to obtain a core intermediate; mixing the core intermediate with a Q source, and performing a second sintering treatment to obtain a core; performing a multi-stage mixing treatment on the core and a carbon material, and performing a third sintering treatment, where the multi-stage mixing treatment at least includes a first-stage mixing treatment and a second-stage mixing treatment performed in sequence. The rotation speed of the first-stage mixing treatment is P1, with the unit of rpm, and the time of the first-stage mixing treatment is H1, with the unit of min; the rotation speed of the second-stage mixing treatment is P2, with the unit of rpm, and the time of the second-stage mixing treatment is H2, with the unit of min, and 3.0 ≤ P2 / P1 ≤ 8.0, 5 ≤ H2 / H1 ≤ 15. Thus, by reasonably setting the multi-stage carbon coating process, the mixing uniformity of the core and the carbon material can be effectively improved, the core can be reduced from cracking and generating internal microcracks during the coating process, thereby enhancing the bonding strength between the carbon material and the core, and obtaining a cathode active material with an appropriate equivalent particle size. This method can be applied to various different types of carbon materials.

[0016] In some embodiments, 100 rpm ≤ P1 ≤ 500 rpm, 400 rpm ≤ P2 ≤ 2000 rpm. Thus, it helps to improve the mixing uniformity of the core and the carbon material, and reduce the core from cracking and generating internal microcracks during the coating process.

[0017] In some embodiments, 1 min ≤ H1 ≤ 15 min, 10 min ≤ H1 ≤ 60 min. Thus, it helps to improve the mixing uniformity of the core and the carbon material, and reduce the core from cracking and generating internal microcracks during the coating process.

[0018] In some embodiments, the constant temperature T3 of the third sintering treatment is 100°C - 500°C, optionally 150°C - 450°C; the constant temperature time t3 of the third sintering treatment is 1 h - 8 h, optionally 2 h - 6 h. Thereby, it helps to improve the bonding strength between the carbon coating layer and the core.

[0019] In some embodiments, the constant temperature T1 of the first sintering treatment is 900°C - 1100°C, and the constant temperature time t1 of the first sintering treatment is 15 h - 35 h. Thereby, it helps to form a core with a relatively high particle size consistency.

[0020] In some embodiments, the constant temperature T2 of the second sintering treatment is 700°C - 900°C, and the constant temperature time t2 of the second sintering treatment is 8 h - 15 h. Thereby, element Q can be incorporated into the core to improve the chemical stability of the core.

[0021] In some embodiments, the sodium source includes one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium nitrate, sodium sulfate, sodium chloride, sodium fluoride, and sodium sulfide; and / or, the M source includes one or more of the oxide, sulfide, hydroxide, hydroxyoxide, oxyacid, sulfate, carbonate, oxalate, phosphate, nitrate, and fluoride corresponding to element M; and / or, the Q source includes one or more of the oxide, sulfide, hydroxide, oxyacid, carbonate, oxalate, phosphide, fluoride, and hydroxyoxide corresponding to element Q. Thereby, the raw material sources are rich, the environmental pollution is small, the compatibility with the production line is good, and it helps to reduce the manufacturing cost.

[0022] In the third aspect of the present application, a positive electrode tab is proposed, which includes a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector. The positive electrode active material layer includes the aforementioned positive electrode active material or the positive electrode active material prepared by the aforementioned method. Thereby, the positive electrode tab has all the characteristics and advantages of the aforementioned positive electrode active material and its preparation method, which will not be elaborated here.

[0023] In the fourth aspect of the present application, a sodium-ion battery is proposed, which includes the aforementioned positive electrode tab. Thereby, the sodium-ion battery has all the characteristics and advantages of the aforementioned positive electrode tab, which will not be elaborated here. In summary, the sodium-ion battery has a lower initial impedance and better cycling performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description of the embodiments in conjunction with the accompanying drawings, where:

[0025] Figure 1This is a scanning electron microscope image of the positive electrode active material in Example 1 of this application at a magnification of 30K.

[0026] Figure 2 This is a scanning electron microscope image of the positive electrode active material in Example 1 of this application at a magnification of 10K.

[0027] Figure 3 This is a scanning electron microscope image of the positive electrode active material in Comparative Example 1 of this application at a magnification of 30K.

[0028] Figure 4 This is a scanning electron microscope image of the positive electrode active material in Comparative Example 1 of this application at a magnification of 10K.

[0029] Figure 5 This is the Nyquist plot of the batteries in Example 1 and Comparative Example 1 of this application at 100% SOC.

[0030] Figure 6 This is a comparison chart of the cycling performance of the batteries in Example 1 and Comparative Example 1 of this application under the conditions of 2.0V - 4.1V and room temperature. Detailed Description of the Embodiments

[0031] The embodiments of the present application will be described in detail below. The examples of the embodiments are shown in the drawings, but there may be cases where unnecessary details are omitted. For example, there may be cases where the detailed description of well-known matters is omitted and the repeated description of actually identical structures is omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0032] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application; unless otherwise stated, the numerical values of the various parameters mentioned in this application can be measured by various commonly used measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of this application).

[0033] The terms "comprising" and "having" and any variations thereof in the description and claims of this application are open-ended expressions, that is, they include the content specified in this application, but do not exclude other aspects.

[0034] In the description of this application, all the numbers disclosed herein are approximate values, whether or not words such as "about" or "approximately" are used. There may be a difference of less than 10% in the numerical value of each number or a reasonable difference considered by those skilled in the art, such as a difference of 1%, 2%, 3%, 4% or 5%.

[0035] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the specific range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4 and 2 - 5. In this application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] In the description of this application, "A and / or B" can include the case of A alone, the case of B alone, and any one of the cases of A and B, where A and B are only for example and can be any technical features connected by "and / or" in this application.

[0037] In this application, the written order of each step does not mean a strict execution order that constitutes any limitation on the implementation process. The specific execution order of each step should be determined according to its function and possible internal logic. If there is no special instruction, all the steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or can also include steps (a), (c) and (b), or can also include steps (c), (a) and (b), etc.

[0038] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0039] Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0040] There are problems with layered transition metal oxides such as poor electronic conductivity and the formation of a passivation layer due to unstable side reactions on the surface, resulting in problems such as a relatively large initial impedance of the positive electrode active material and a relatively high impedance growth rate during cycling, severely limiting its large-scale application in the fields of power and energy storage.

[0041] The coating strength and coating uniformity of the carbon coating layer on the surface of the core have an important impact on the impedance of the positive electrode active material. In the present application, the equivalent particle size can intuitively reflect the tightness of the fit and the uniformity of the distribution of the carbon coating layer on the surface of the core. When the equivalent particle size D of the positive electrode active material is 0.78 μm - 2.04 μm, the carbon material in the carbon coating layer is uniformly distributed on the surface of the core and is relatively tightly attached to the core. The carbon material does not agglomerate by itself or is separately dispersed between the positive electrode particles, so that an effective conductive network can be formed under the premise of a relatively low carbon addition amount, effectively protecting the surface of the positive electrode active material, thereby reducing the initial impedance and reducing the impedance growth during cycling, and at the same time helping to improve the specific capacity of the positive electrode active material.

[0042] It should be noted that in the present application, the positive electrode active material is regarded as a standard sphere or a sphere-like body, and it is considered that there is no pore structure in the positive electrode active material particles that communicates with the outer surface, that is, the positive electrode active material is relatively dense. Therefore, the radius of the positive electrode active material is regarded as the radius of a standard sphere with the same volume.

[0043] The equivalent particle size D (unit: μm) of the positive electrode active material is calculated from the specific surface area S (unit: m 2 / g) and the tapped density T (unit: g / cm 3 ), and the specific calculation is as follows:

[0044] For a single positive electrode active material particle: the specific surface area S of the positive electrode active material particle is equal to the surface area of the positive electrode active material divided by the mass of the positive electrode active material particle. Among them, the surface area of the positive electrode active material is 4πr 2 , and the mass of the positive electrode active material is the product of the volume of the positive electrode active material particle and the tapped density T of the positive electrode active material particle. Among them, the volume of the positive electrode active material particle is 4 / 3πr 3 , and since the equivalent radius r = D / 2, that is, D = 2r. As can be seen from the above,

[0045] S = (4πr 2 ) / (4 / 3πr3 (r × T) = 3 / (r × T), and by substitution, we get D = 2 × 3 / (S × T) = 6 / (S × T).

[0046] In the first aspect of the present application, a positive electrode active material is proposed, including: a core, and a carbon coating layer located on at least a part of the surface of the core; the equivalent particle size D of the positive electrode active material is 0.78 μm - 2.04 μm, D = 6 / (S × T), where S is the specific surface area of the positive electrode active material, with the unit of m 2 / g; T is the tapped density of the positive electrode active material, with the unit of g / cm 3 . Thus, the carbon coating layer fits tightly with the core, and the positive electrode active material has better structural stability. An effective conductive network can be formed with a small amount of carbon material, effectively protecting the surface of the core.

[0047] As an example, the equivalent particle size D of the positive electrode active material can be 0.78 μm, 0.85 μm, 0.88 μm, 0.98 μm, 1.08 μm, 1.18 μm, 1.28 μm, 1.38 μm, 1.48 μm, 1.58 μm, 1.68 μm, 1.78 μm, 1.82 μm, 1.88 μm, 1.98 μm or 2.04 μm.

[0048] When the equivalent particle size D of the positive electrode active material is within the aforementioned range, the carbon material in the carbon coating layer fits tightly and is evenly distributed on the surface of the core, which can effectively reduce the resistance of electron transfer and improve the kinetic characteristics of the material. The carbon coating layer can also improve the interfacial compatibility between the positive electrode active material and the electrolyte. While reducing the side reactions between the positive electrode active material and the electrolyte, it can also make the electrolyte better infiltrate the surface of the positive electrode active material, increase the contact between the positive electrode plate and the electrolyte, and improve the ion transfer efficiency. In addition, during the charge and discharge process of the battery, the positive electrode active material will undergo volume changes. The carbon coating layer has a certain flexibility and elasticity, which can buffer the volume changes of the positive electrode active material during the charge and discharge process, reduce the generation of internal stress, maintain the structural integrity, and improve the cycle stability.

[0049] In some embodiments, D is 0.85 μm - 1.82 μm. Thus, the carbon coating layer fits tightly with the core and has a moderate coating strength.

[0050] In some embodiments, S is 1.4 m 2 / g - 3.2 m 2 / g; optionally, 1.5 m 2 / g - 3.0 m 2 / g. Thus, the positive electrode active material has a smaller specific surface area and fewer side reactions with the electrolyte.

[0051] As an example, S can be 1.4 m 2 / g, 1.5 m 2 / g, 1.6 m 2 / g, 1.8 m 2 / g, 2.0 m 2 / g, 2.2 m 2 / g, 2.4 m 2 / g, 2.6 m 2 / g, 2.8 m 2 / g, 3.0 m 2 / g or 3.2 m 2 / g.

[0052] As an example, the specific surface area S can be measured by the nitrogen adsorption method. Specifically, first, accurately weigh 4 g of the positive electrode active material sample and place it at the bottom of the sample tube. Then, install the sample tube containing the sample on the vacuum degassing device and evacuate and degas it at 300 °C for 1 hour to completely remove the impurities and moisture adsorbed on the surface of the sample. After the degassing is completed, keep the sample tube in a vacuum state and cool it to room temperature. Quickly install the degassed sample tube on the sample test position of the specific surface area analyzer, and add liquid nitrogen to the Dewar bottle to maintain a low-temperature environment (77 K). Start the vacuum pump again to evacuate the test system until the required vacuum degree is reached. Slowly fill a certain amount of high-purity nitrogen into the test chamber to gradually increase the pressure in the test chamber to the first predetermined relative pressure point (K1 / K0) (generally selected in the range of 0.05 - 0.35). After the pressure stabilizes, record the pressure (K1) and adsorption amount (U1) at this time. The adsorption amount can be calculated by the instrument according to the gas equation from the pressure change. According to the above steps, sequentially increase the nitrogen pressure to reach different relative pressure points (K2 / K0), (K3 / K0), (K4 / K0), (K5 / K0), etc., and record the corresponding pressure and adsorption amount data. After the adsorption process is completed, slowly reduce the nitrogen pressure in the test chamber to carry out the desorption process. At each desorption pressure point, record the pressure and desorption amount data until the pressure returns to the initial vacuum state. After collecting the nitrogen adsorption - desorption isotherm, perform a linear fit through the BET equation, and plot a curve with K / K0 as the horizontal axis and the adsorption amount U as the vertical axis. After calculating the monolayer saturated adsorption amount Um, combined with the cross-sectional area of the nitrogen molecule (0.162 nm 2 ), and the sample mass W, substitute into the formula S = (Um × N × Am) / (22400 × W) to obtain the specific surface area.

[0053] In some embodiments, T is 2.1 g / cm 3 -2.4 g / cm 3 ; optionally, 2.20 g / cm 3 -2.35 g / cm 3Thus, the tap density of the positive electrode active material is relatively high, and the internal voids in the positive electrode active material layer can be reduced.

[0054] As an example, T can be 2.1 g / cm 3 , 2.15 g / cm 3 , 2.2 g / cm 3 , 2.25 g / cm 3 , 2.3 g / cm 3 , 2.35 g / cm 3 or 2.4 g / cm 3 .

[0055] As an example, the tap density T can be measured by the following method. Specifically, accurately weigh 35 g of the positive electrode active material sample and place it in a 25 mL graduated cylinder. Fix the graduated cylinder on a tap density tester, set the number of vibrations to 3000 times, the amplitude to 3 mm, and the frequency to 250 times / minute. Start the instrument, stop it after 3000 vibrations, read the volume of the powder after tapping, and divide the sample mass by the volume of the powder after tapping to obtain the tap density T of the material.

[0056] In some embodiments, the carbon coating layer includes carbon particles distributed on the surface of the inner core, and the particle size of the carbon material therein is less than or equal to 50 nm.

[0057] When the particle size of the carbon material in the carbon coating layer is within the aforementioned range, it helps the carbon material to uniformly cover the surface of the positive electrode material, forming a continuous and dense coating layer.

[0058] In some embodiments, the specific surface area of the carbon material in the carbon coating layer is greater than or equal to 100 m 2 / g.

[0059] When the specific surface area of the carbon material in the carbon coating layer is within the aforementioned range, the carbon particles with a high specific surface area can provide more surface active sites, enhance the binding force with the inner core, and form a more stable coating layer.

[0060] In some embodiments, the oil absorption value of the carbon material in the carbon coating layer is greater than or equal to 250 mL / g. Thus, it helps the carbon coating layer to be uniformly distributed on the surface of the inner core.

[0061] When the oil absorption value of the carbon material in the carbon coating layer is within the aforementioned range, the carbon particles can be embedded in the surface pores of the inner core, forming a mechanical interlocking effect, enhancing the binding strength between the coating layer and the inner core, and inhibiting the structural collapse of the inner core during the cycling process.

[0062] In some embodiments, the mass fraction of the carbon coating layer in the positive electrode active material is 0.5wt%-3.0wt%; alternatively, 0.8wt%-1.5wt%. Thus, the positive electrode active material has both excellent conductivity and high specific capacity.

[0063] As an example, the mass fraction of the carbon coating layer in the positive electrode active material may be 0.5 wt%, 0.8 wt%, 1.1 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.5 wt%, 2.8 wt% or 3 wt%.

[0064] When the mass fraction of the carbon coating layer in the positive electrode active material is within the aforementioned range, within the aforementioned equivalent particle size range, a small amount of carbon coating layer can form an effective conductive network and reduce the side reaction between the core and the electrolyte, while having little effect on the gram capacity of the positive electrode active material.

[0065] In some embodiments, the carbon material in the carbon coating layer includes one or more of acetylene black, Super P, Ketjen black, conductive graphite, carbon nanotubes, and graphene. Thus, the carbon coating layer has better conductivity.

[0066] In some embodiments, the compaction density of the positive electrode active material at a pressure of 2T is 3.2 g / cm 3 -3.5g / cm 3 ; Optionally, 3.25 g / cm 3 -3.40g / cm 3 This helps to improve the volume energy density of the battery using the positive electrode active material.

[0067] As an example, the compaction density of the positive electrode active material at a pressure of 2T may be 3.2 g / cm 3 , 3.25g / cm 3 , 3.3g / cm 3 、3.35g / cm 3 、3.4g / cm 3 、3.45g / cm 3 or 3.5g / cm 3 .

[0068] In some embodiments, the repose angle of the positive electrode active material is less than or equal to 43°; optionally, less than or equal to 40°. This helps to evenly coat the positive electrode active material on the surface of the positive electrode current collector and reduces the risk of cracking of the positive electrode active material layer.

[0069] When the angle of repose (i.e., the angle of repose) of the positive electrode active material is within the aforementioned range, the frictional force between the positive electrode active material particles is small, the cohesive force is weak, and the fluidity of the positive electrode active material is good, which is conducive to forming a positive electrode active material layer with a uniform thickness and reducing the formation of defects such as cracks and holes.

[0070] As an example, the angle of repose can be determined according to GBT6609.24-2004 Determination of the Angle of Repose of Physical Properties, specifically as follows: In a drying room, 50 g of the positive electrode active material is added to a funnel (equipped with a stainless steel screen at the inlet), and the material is allowed to fall naturally through the funnel opening onto a smooth bottom plate. The angle of repose of the material is obtained by measuring the height of the accumulated material and then through conversion.

[0071] In some embodiments, the oxygen defect concentration of the positive electrode active material is 2.5% - 4.5%. Thus, vacancies can be formed in the structure of the positive electrode active material, which is beneficial to the transmission of sodium ions, and can also alleviate the structural stress change of the positive electrode active material during charge and discharge.

[0072] As an example, the oxygen defect concentration of the positive electrode active material can be 2.5%, 3%, 3.5%, 4%, or 4.5%.

[0073] When the oxygen defect concentration of the positive electrode active material is within the aforementioned range, some vacancies or channels can be formed in the positive electrode active material, which is beneficial to the transmission of sodium ions, enabling sodium ions to be more smoothly inserted and extracted during charge and discharge, thereby improving the rate performance of the battery; the existence of oxygen defects can also change the electron cloud distribution and electronic structure, improve the electronic conductivity of the positive electrode active material, and contribute to improving the charge and discharge efficiency and overall performance of the battery. In addition, a certain amount of oxygen defects can alleviate the structural stress change of the positive electrode active material to a certain extent during charge and discharge, enhance the structural stability, and then improve the cycle performance of the battery and reduce the capacity attenuation during the cycle.

[0074] As an example, the internal oxygen defect concentration (relative content) of the positive electrode active material can be obtained through X-ray photoelectron spectroscopy (XPS) test analysis. Specifically: Use an XPS instrument to test the positive electrode active material sample, then use the Shirley background subtraction method for background subtraction, and then use the C1s peak (binding energy of 284.6 eV) as a reference to calibrate the binding energies of other elements to eliminate the binding energy shift caused by factors such as the instrument itself or sample charging. Due to the existence of oxygen defects, the O 1s peak will show phenomena such as asymmetry / splitting, and it is decomposed into different sub-peaks by using the peak fitting method. Generally speaking, the sub-peak related to oxygen defects usually appears at a binding energy position lower than that of normal lattice oxygen.

[0075] Relative content calculation: Based on the sub-peak area (or intensity) related to oxygen defects obtained by fitting and the total O1s peak area (or intensity), the relative content of oxygen defects relative to the total oxygen can be calculated. Assume the sub-peak area related to oxygen defects is A vacancy , and the total O1s area is A total , then the relative content C vacancy of oxygen vacancies = A vacancy / A total × 100%.

[0076] In some embodiments, the core satisfies the chemical formula: Na a (Ni 1-b-c-d Fe b Mn c M d )Q e O 2-f , where 0.95 ≤ a ≤ 1.10, 0.03 ≤ b ≤ 0.50, 0.03 ≤ c ≤ 0.50, 0 ≤ d ≤ 0.15, 0 ≤ e ≤ 0.10, 0 ≤ f ≤ 0.25, and the value of f is required to ensure that the positive and negative charges of each ion in the core are equal; M includes one or more of V, Ta, Cr, La, Al, Ce, Y, Mg, Sr, Ba, Ra, Zr, Ca, Zn, B, W, Nb, Cd, Pb, Si, Mo, Co, Li, Ti, and Cu, and Q includes one or more of V, Ta, Cr, La, Al, Ce, Y, Mg, Sr, Ba, Ra, Zr, Ca, Zn, B, W, Nb, Cd, Pb, Si, Mo, F, P, Co, Li, Ti, and Cu. Thus, by doping with different elements, cathode active materials that meet different performance requirements can be obtained.

[0077] Doping with the M element can stabilize the structure of the transition metal layer in the layered metal oxide and improve the structural stability of the cathode active material at high voltages.

[0078] Doping with the Q element can form a stable protective layer on the surface layer of the core, remove the residual alkali on the core surface, effectively inhibit the side reaction between the cathode active material and the electrolyte, and improve the cycling performance.

[0079] In the second aspect of the present application, the present application proposes a method for preparing the aforementioned cathode active material. By reasonably setting a multi-stage carbon coating process, the mixing uniformity of the core and the carbon material can be effectively improved, the core cracking and internal microcracks generated during the coating process can be reduced, and the bonding strength between the carbon material and the core can be enhanced. Thus, single-crystal cathode active materials with appropriate equivalent particle sizes can be obtained. Specifically, the method includes:[[]]

[0080] S100: Mix a nickel source, an iron source, a manganese source, a complexing agent, and a precipitating agent to obtain a precursor slurry, and perform a drying treatment to obtain a precursor material.

[0081] In some embodiments, in this step, the nickel source, the iron source, the manganese source, the complexing agent, and the precipitating agent are mixed to carry out a coprecipitation reaction to obtain a precursor slurry, and then the precursor slurry is aged, filtered, washed, and dried to obtain a precursor material.

[0082] In some embodiments, the nickel source, the iron source, and the manganese source each independently include at least one of sulfates, chlorides, and acetates of the corresponding elements. Thus, the raw material sources are rich, the environmental pollution is small, and it helps to reduce the manufacturing cost.

[0083] In some embodiments, the complexing agent includes at least one of ammonia water, sodium oxalate, sodium citrate, and ethylenediaminetetraacetic acid. Thus, the raw material sources are rich, the environmental pollution is small, it can be adapted to conventional process production lines, and it helps to reduce the manufacturing cost.

[0084] In some embodiments, the precipitating agent includes at least one of sodium hydroxide and sodium carbonate. Thus, the raw material sources are rich, the environmental pollution is small, it can be adapted to conventional process production lines, and it helps to reduce the manufacturing cost.

[0085] As an example, the feeding ratios of the nickel source, the iron source, and the manganese source can be calculated according to the stoichiometric ratios of the corresponding elements in the target product. The complexing agent and the precipitating agent can be fed in reasonable proportions according to the dosages of the nickel source, the iron source, and the manganese source.

[0086] S200: Mix the precursor material, a sodium source, and an M source, and perform a first sintering treatment to obtain a core intermediate.

[0087] In some embodiments, in this step, the previously prepared precursor material is mixed with the sodium source and the M source, and then through a first sintering treatment, as well as crushing and sieving treatments to obtain a core intermediate.

[0088] By adding the M source as a dopant in this step, the effect of uniform bulk doping and stabilizing the structure of the cathode active material can be achieved.

[0089] In some embodiments, the constant temperature temperature T1 of the first sintering treatment is 900°C - 1100°C, and the constant temperature time t1 of the first sintering treatment is 15h - 35h. Thus, it helps to form a core with a relatively high particle size consistency.

[0090] As an example, the constant temperature temperature T1 of the first sintering treatment can be 900°C, 950°C, 1000°C, 1050°C, or 1100°C.

[0091] As an example, the isothermal time t1 of the first sintering treatment can be 15 h, 20 h, 25 h, 30 h or 35 h.

[0092] As an example, the sintering atmosphere of the first sintering treatment is air.

[0093] In some embodiments, the sodium source includes one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium nitrate, sodium sulfate, sodium chloride, sodium fluoride, and sodium sulfide.

[0094] In some embodiments, the M source includes one or more of an oxide, sulfide, hydroxide, hydroxyoxide, oxyacid, sulfate, carbonate, oxalate, phosphate, nitrate, and fluoride corresponding to the M element.

[0095] As an example, the feeding ratio of the precursor material, sodium source, and M source can be calculated according to the stoichiometric ratio of the corresponding elements in the target product.

[0096] S300: Mix the core intermediate with the Q source and perform a second sintering treatment to obtain the core

[0097] In some embodiments, in this step, the prepared core intermediate is mixed with the Q source, and after the second sintering treatment, as well as crushing and sieving treatments, the core is obtained. By adding the coating agent Q source, a stable protective layer can be formed on the surface of the core, which plays a role in stabilizing the core structure and removing residual alkali on the surface of the core.

[0098] In some embodiments, the isothermal temperature T2 of the second sintering treatment is 700°C - 900°C, and the isothermal time t2 of the second sintering treatment is 8 h - 15 h. Thus, the Q element can be incorporated into the core to improve the chemical stability of the core.

[0099] As an example, the isothermal temperature T2 of the second sintering treatment can be 700°C, 750°C, 800°C, 850°C or 900°C.

[0100] As an example, the isothermal time t2 of the second sintering treatment can be 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h or 15 h.

[0101] As an example, the sintering atmosphere of the second sintering treatment can be air.

[0102] In some embodiments, the Q source includes one or more of an oxide, sulfide, hydroxide, oxyacid, carbonate, oxalate, phosphide, fluoride, and hydroxyoxide corresponding to the Q element. Thus, the raw material sources are rich, the environmental pollution is small, the compatibility with the production line is good, and it helps to reduce the manufacturing cost.

[0103] As an example, the feeding ratio of the core intermediate to the Q source can be calculated according to the stoichiometric ratio of the corresponding elements in the target product.

[0104] S400: Perform multi-stage mixing treatment on the core and the carbon material, and perform the third sintering treatment

[0105] In some embodiments, in this step, the core and the carbon material are coated and mixed, and after the third sintering treatment and sieving, a single-crystalline cathode active material is obtained. Among them, the multi-stage mixing treatment at least includes a first-stage mixing treatment and a second-stage mixing treatment performed in sequence. The rotation speed of the first-stage mixing treatment is P1, with the unit of rpm, and the time of the first-stage mixing treatment is H1, with the unit of min; the rotation speed of the second-stage mixing treatment is P2, with the unit of rpm, and the time of the second-stage mixing treatment is H2, with the unit of min, 3.0 ≤ P2 / P1 ≤ 8.0, 5 ≤ H2 / H1 ≤ 15.

[0106] As an example, P2 / P1 can be 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5 or 8.0.

[0107] As an example, H2 / H1 can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15.

[0108] By reasonably setting the multi-stage carbon coating process, the mixing uniformity of the core and the carbon material can be effectively improved, thereby effectively enhancing the distribution uniformity of the carbon material on the surface of the core, which helps to form a uniformly coated and moderately coated layer through subsequent low-temperature sintering treatment.

[0109] In some embodiments, 100 rpm ≤ P1 ≤ 500 rpm, 400 rpm ≤ P2 ≤ 2000 rpm. Thus, it helps to improve the mixing uniformity of the core and the carbon material, and reduce the rupture of the core and the generation of internal microcracks during the coating process.

[0110] As an example, P1 can be 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm.

[0111] As an example, P2 can be 400 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1400 rpm, 1600 rpm, 1800 rpm or 2000 rpm.

[0112] In some embodiments, 1 min ≤ H1 ≤ 15 min, 10 min ≤ H1 ≤ 60 min. Thereby, it helps to improve the mixing uniformity of the core and the carbon material, and reduce the cracking of the core and the generation of internal microcracks during the coating process.

[0113] As an example, H1 can be 1 min, 3 min, 7 min, 9 min, 11 min, 13 min or 15 min.

[0114] As an example, H2 can be 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min.

[0115] In some embodiments, the constant temperature T3 of the third sintering treatment is 100°C - 500°C, optionally 150°C - 450°C; the constant temperature time t3 of the third sintering treatment is 1 h - 8 h, optionally 2 h - 6 h. Thereby, it helps to improve the bonding strength between the carbon coating layer and the core.

[0116] As an example, the constant temperature T3 of the third sintering treatment can be 100°C, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C or 500°C.

[0117] As an example, the constant temperature time t3 of the third sintering treatment can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h.

[0118] By performing the third sintering treatment on the core and the carbon material that have undergone multi-stage mixing treatment, the bonding force and the degree of fit between the carbon material and the core are enhanced, and the two are closely fitted through strong van der Waals forces, which helps to form a stable and efficient conductive network with a low carbon addition amount.

[0119] The temperature of the third sintering treatment is relatively low. Under suitable constant temperature and time, it helps to make the carbon material more evenly distributed and more closely attached to the surface of the single crystal core particles, forming a conductive network and a protective barrier. Performing the third sintering treatment in an inert atmosphere helps some oxygen atoms in the core to escape from the lattice due to energy effects and other reasons, thereby generating an appropriate amount of oxygen defects. The appropriate amount of oxygen defects can provide additional channels and sites for the transport of sodium ions, which is beneficial to increasing the sodium ion diffusion coefficient of the positive electrode active material and enhancing the electrochemical activity of the material.

[0120] As an example, the sintering atmosphere of the third sintering treatment is an inert atmosphere, which can include, for example, N2, Ar, He, etc.

[0121] The third sintering treatment is carried out in an inert atmosphere (instead of the traditional oxidation atmosphere), which not only helps to reduce the loss of carbon materials caused by the heat treatment of the carbon materials on the surface of the core in the oxidation atmosphere, but also can generate certain oxygen defects inside the core by matching the temperature and time of the third sintering treatment.

[0122] As an example, the feeding ratio of the core to the carbon material can be calculated according to the designed value of the mass fraction of the carbon coating layer in the target product.

[0123] In the third aspect of the present application, the present application provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector. The positive electrode active material layer includes the aforementioned positive electrode active material or the positive electrode active material prepared by the aforementioned method. Thus, the positive electrode sheet has all the characteristics and advantages of the aforementioned positive electrode active material and its preparation method, which will not be elaborated here.

[0124] In the fourth aspect of the present application, the present application provides a sodium ion battery, which includes the aforementioned positive electrode sheet. Thus, the sodium ion battery has all the characteristics and advantages of the aforementioned positive electrode sheet, which will not be elaborated here. In general, the sodium ion battery has a lower initial impedance and better cycling performance.

[0125] The solution of the present application will be described below through specific examples. It should be noted that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specifying specific techniques or conditions in the examples, they shall be carried out according to the techniques or conditions described in the literature in the field or according to the product specifications. For the reagents or instruments not indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0126] Example 1

[0127] A nickel source (nickel sulfate), an iron source (ferrous sulfate), and a manganese source (manganese sulfate) are mixed according to the molar ratio of nickel, iron, and manganese metal elements of 33.3 / 33.3 / 33.3 to obtain a ternary solution (the concentration of the ternary solution is 90 g / L). Then, nitrogen gas, a sodium hydroxide solution (alkali concentration 10 g / L), and an ammonia water solution (ammonia concentration 6 g / L) are introduced into the reaction bottom solution for coprecipitation reaction to obtain a precursor slurry. Then, the above slurry is aged, filtered, washed, and dried to obtain a precursor material, and the molar ratio of each element of the precursor satisfies Ni / Fe / Mn = 1 / 1 / 1;

[0128] Mix the obtained precursor material, sodium source (sodium carbonate), and M source (containing Ti and Ca) evenly, where the mixing molar ratio satisfies Na / M = 1.0, and the molar ratios of the remaining elements satisfy Ni / Fe / Mn / Ti / Ca = 0.322 / 0.322 / 0.322 / 0.018 / 0.015; conduct the first sintering treatment on the mixture in air, T1 = 1000 °C, t1 = 30 h; and successively perform crushing and sieving to obtain the core intermediate.

[0129] Mix the obtained core intermediate with the Q source (containing Al), where the molar ratios of the elements satisfy Ni / Fe / Mn / Ti / Ca / Al = 0.319 / 0.319 / 0.319 / 0.018 / 0.015 / 0.010; conduct the second sintering treatment in an air atmosphere, T2 = 780 °C, t2 = 12 h; and successively perform crushing and sieving to obtain the core, whose chemical formula is: Na 1.000 (Ni 0.319 Fe 0.319 Mn 0.319 Ti 0.018 Ca 0.015 )Al 0.010 O2.

[0130] Mix the obtained core with carbon material (Super P, particle size of 40 nm, specific surface area of 120 m 2 / g, oil absorption value of 280 mL / g) by multi-stage mixing treatment, and then conduct the third sintering treatment on it in a nitrogen atmosphere, T3 = 300 °C, t3 = 4 h; obtain the positive electrode active material after sieving.

[0131] The remaining examples, comparative examples are consistent with Example 1, and the differences are shown in Tables 1-1 and 1-2. Among them, in Comparative Example 1, no carbon material is added during the carbon coating process on the core surface, that is, no carbon coating is performed, and only the core material undergoes the remaining same processes.

[0132]

[0133]

[0134]

[0135] The parameters of the positive electrode active materials prepared in the foregoing examples and comparative examples are shown in Table 2.

[0136] Table 2

[0137]

[0138] Assemble the positive electrode active materials in the foregoing examples and comparative examples into CR2032 button cells, and the assembly method is as follows:

[0139] The above-mentioned positive electrode active material, conductive carbon and binder PVDF are mixed in N-methylpyrrolidone in a mass ratio of 95:3:2 (the amount of conductive carbon added in the pulping process is reduced accordingly according to the amount of conductive carbon coating on the sample, so that the mass ratio of the positive electrode active material to the conductive carbon (the sum of the conductive carbon coating amount of the positive electrode active material and the conductive carbon additionally added in the pulping) and the binder in the final pulping process still meets 95:3:2, and are fully mixed to form a uniform slurry. The slurry is coated on aluminum foil and dried in an oven at 120°C for 12h, and is stamped into a positive electrode sheet with a diameter of 12mm and a thickness of 120mm using a pressure of 100MPa, wherein the loading amount of the positive electrode active material is 15mg / cm 2 .

[0140] In an argon-filled glove box, the aforementioned positive electrode sheet, separator, negative electrode sheet and electrolyte were assembled into a CR2032 button cell. The negative electrode sheet used a metal sodium sheet; the separator used a polypropylene film; the solvent of the electrolyte was an equal volume mixture of ethylene carbonate, diethyl carbonate and vinylene carbonate, the electrolyte salt in the electrolyte was NaPF6, and the concentration of NaPF6 in the electrolyte was 1 mol / L.

[0141] The button cell assembled above was tested as follows. The test results are shown in Table 3:

[0142] Electrochemical impedance spectroscopy (EIS) test: Take the unactivated half-cell prepared above, let it stand for 6 hours, then charge it to 4.1V (cut-off current 0.05C) at a constant current and voltage of 0.1C, then discharge it to 2.0V at a constant current and voltage of 0.1C; then charge it to 4.1V (cut-off current 0.05C) at a constant current and voltage of 0.1C, remove the fully charged half-cell, and perform EIS test in the frequency range of 1MHz to 0.01Hz, with an amplitude of 10mV. According to the formula: Z re =R s +R ct +σω -1 / 2 , and ω=2πf, the EIS impedance is calculated. re is the real part of the impedance spectrum obtained by the test, R s is the solution resistance, R ct is the charge transfer resistance, ω is the angular frequency, f is the test frequency, and σ is the Warburg factor; EIS impedance R = R s +R ct .

[0143] Capacity rate test: At 25 °C, the charge and discharge range is 2.0V - 4.1V. Cycle at 0.1C for 2 weeks, and then cycle once at 0.2C, 0.33C, 0.5C, and 1C respectively. The specific discharge capacity at 0.1C for the first time is the specific discharge capacity of the first week of cycling of the button cell.

[0144] 80-cycle capacity retention rate test: After the above rate test, continue to perform 80-week cyclic charge and discharge tests at a rate of 1C. Evaluate the battery capacity retention rate by dividing the discharge capacity of the last week of cycling by the discharge capacity of the first week of cycling at the beginning.

[0145] Table 3

[0146]

[0147]

[0148] The test results show that:

[0149] Figure 1 Figure 2 They are SEM photos of the sample of Example 1 at different magnification ratios respectively. Figure 3 Figure 4 They are SEM photos of the sample of Comparative Example 1 at different magnification ratios respectively. Figure 5 and Figure 6 They are the Nyquist diagrams and the comparison diagrams of room temperature cycling of Example 1 and Comparative Example 1 at 100% SOC respectively.

[0150] In the examples, the carbon coating layer and the core of the positive active material are relatively closely adhered, and the structure stability of the positive active material is relatively excellent. An effective conductive network can be formed with a small amount of carbon material to effectively protect the surface of the core. As a result, the initial impedance of the battery in the examples is relatively low, and the cycling performance is relatively excellent, both of which are superior to the electrical performance of the batteries in the comparative examples. When the D value of the positive active material is too small, the carbon material adheres too closely to the surface of the positive electrode, and the coating strength is too high, resulting in the core being broken or microcracks being generated inside during the coating process, and the electrochemical performance deteriorates. When the D value of the positive active material is too large, the combination between the carbon material and the core is too loose, the distribution is uneven, and the conductivity of the core cannot be improved after coating, and the effect of reducing surface side reactions is poor, and the electrochemical performance is poor.

[0151] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments with the same structure and the same function and effect as the technical idea within the technical solution scope of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the main idea of this application, various deformations that can be thought of by those skilled in the art on the embodiments and other ways constructed by combining some constituent elements of the embodiments are also included in the scope of this application.

Claims

1. A positive electrode active material, characterized in that, Comprising: A core, A carbon coating layer located on at least a part of the surface of the core; The equivalent particle size D of the positive electrode active material is 0.78 μm - 2.04 μm, D = 6 / (S×T), where S is the specific surface area of the positive electrode active material, with the unit of m 2 / g; T is the tapped density of the positive electrode active material, with the unit of g / cm 3 .

2. The cathode active material according to claim 1, characterized in that, D is 0.85 μm - 1.82 μm.

3. The positive electrode active material according to claim 1, wherein, S is 1.4 m 2 / g - 3.2 m 2 / g; optionally, 1.5 m 2 / g - 3.0 m 2 / g.

4. The positive electrode active material according to claim 3, characterized in that, T is 2.1 g / cm 3 -2.4 g / cm 3 ; Optionally, 2.20 g / cm 3 -2.35 g / cm 3 .

5. The cathode active material according to any one of claims 1-4, characterized in that, The carbon material in the carbon coating layer satisfies at least one of the following conditions: The particle size is less than or equal to 50 nm; The specific surface area is greater than or equal to 100 m 2 / g; The oil absorption value is greater than or equal to 250 mL / g.

6. The cathode active material according to claim 5, wherein The mass fraction of the carbon coating layer in the positive electrode active material is 0.5 wt% - 3.0 wt%; optionally, 0.8 wt% - 1.5 wt%; and / or, The carbon material in the carbon coating layer includes one or more of acetylene black, SuperP, Ketjen black, conductive graphite, carbon nanotubes, and graphene.

7. The cathode active material according to any one of claims 1-4, characterized in that, The tap density of the positive electrode active material under a pressure of 2T is 3.2 g / cm 3 - 3.5 g / cm 3 ; Optionally, 3.25 g / cm 3 - 3.40 g / cm 3 ; And / or, The angle of repose of the positive electrode active material is less than or equal to 43°; optionally, less than or equal to 40°; and / or, The oxygen defect concentration of the positive electrode active material is 2.5% - 4.5%.

8. The positive electrode active material according to any one of claims 1-4, characterized in that, The core satisfies the chemical formula: Na a (Ni 1-b-c-d Fe b Mn c M d )Q e O 2-f , Wherein, 0.95 ≤ a ≤ 1.10, 0.03 ≤ b ≤ 0.50, 0.03 ≤ c ≤ 0.50, 0 ≤ d ≤ 0.15, 0 ≤ e ≤ 0.10, 0 ≤ f ≤ 0.25; M includes one or more of V, Ta, Cr, La, Al, Ce, Y, Mg, Sr, Ba, Ra, Zr, Ca, Zn, B, W, Nb, Cd, Pb, Si, Mo, Co, Li, Ti, and Cu, and Q includes one or more of V, Ta, Cr, La, Al, Ce, Y, Mg, Sr, Ba, Ra, Zr, Ca, Zn, B, W, Nb, Cd, Pb, Si, Mo, F, P, Co, Li, Ti, and Cu.

9. A method for preparing the positive electrode active material according to any one of claims 1-8, characterized in that, Comprising: Mixing a nickel source, an iron source, a manganese source, a complexing agent, and a precipitating agent to obtain a precursor slurry, and performing a drying treatment to obtain a precursor material; Mixing the precursor material, a sodium source, and an M source, and performing a first sintering treatment to obtain a core intermediate; Mixing the core intermediate with a Q source, and performing a second sintering treatment to obtain a core; Performing a multi-stage mixing treatment on the core and a carbon material, and performing a third sintering treatment, Wherein, the multi-stage mixing treatment at least includes a first-stage mixing treatment and a second-stage mixing treatment performed in sequence. The rotation speed of the first-stage mixing treatment is P1, in units of rpm, and the time of the first-stage mixing treatment is H1, in units of min; the rotation speed of the second-stage mixing treatment is P2, in units of rpm, and the time of the second-stage mixing treatment is H2, in units of min, 3.0 ≤ P2 / P1 ≤ 8.0, 5 ≤ H2 / H1 ≤ 15.

10. The method according to claim 9, characterized in that, 100 rpm ≤ P1 ≤ 500 rpm, 400 rpm ≤ P2 ≤ 2000 rpm; and / or, 1 min ≤ H1 ≤ 15 min, 10 min ≤ H1 ≤ 60 min.

11. The method according to claim 9 or 10, characterized in that, The constant temperature of the third sintering treatment is T3 of 100 °C - 500 °C, optionally, 150 °C - 450 °C; the constant temperature time of the third sintering treatment is t3 of 1 h - 8 h, optionally, 2 h - 6 h.

12. The method according to claim 9 or 10, characterized in that The constant temperature T1 of the first sintering treatment is 900 °C - 1100 °C, and the constant temperature time t1 of the first sintering treatment is 15 h - 35 h; and / or, The constant temperature T2 of the second sintering treatment is 700 °C - 900 °C, and the constant temperature time t2 of the second sintering treatment is 8 h - 15 h.

13. The method according to claim 12, wherein The sodium source includes one or more of sodium hydroxide, sodium carbonate, sodium bicarbonate, sodium nitrate, sodium sulfate, sodium chloride, sodium fluoride, sodium sulfide; and / or, The M source includes one or more of the oxide, sulfide, hydroxide, hydroxyoxide, oxyacid, sulfate, carbonate, oxalate, phosphate, nitrate, fluoride of the M element; and / or, The Q source includes one or more of the oxide, sulfide, hydroxide, oxyacid, carbonate, oxalate, phosphide, fluoride, hydroxyoxide of the Q element.

14. A positive electrode sheet, characterized in that, It includes a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material according to any one of claims 1 - 8, or the positive electrode active material prepared by the method according to any one of claims 9 - 13.

15. A sodium-ion battery, characterized in that, It includes the positive electrode plate according to claim 14.

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