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

Abstract

The invention discloses a positive electrode material and a preparation method thereof, a positive electrode plate and a sodium ion battery, and relates to the technical field of batteries, the positive electrode material is a sodium-based layered oxide, and comprises an outer layer wrapping layer and a core aggregate, the core aggregate is embedded in the outer layer wrapping layer, and the inner layer wrapping layer is coated with the core aggregate. The outer wrapping layer at least partially covers the inner core aggregate; the outer wrapping layer is formed by stacking flaky primary particles, the inner core aggregate is formed by interweaving and aggregating granular primary particles, and the average specific surface area of the flaky primary particles is smaller than that of the granular primary particles. By adopting the design, small-particle aggregates are firmly clamped in the middle by large flaky particles, so that the volume change of the small-particle aggregates in the circulating process is limited, and the stress action among the small particles is relieved. And the cycling stability of the material is improved by the synergistic mechanism.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a positive electrode material and a preparation method thereof, a positive electrode sheet and a sodium ion battery. Background Art

[0002] In sodium-ion batteries, layered oxide cathode materials (such as NaXMeO2) have become a research hotspot due to their good ion transport channels and high theoretical specific capacity. However, these materials generally suffer from large volume changes and significant particle expansion or contraction during cycling, leading to particle breakage or pulverization, which significantly affects cycle stability. Therefore, there is an urgent need to develop a new sodium battery cathode material that can reduce volume changes and improve cycle stability through morphology control. Summary of the Invention

[0003] The main purpose of the present invention is to provide a positive electrode material and a preparation method thereof, a positive electrode plate and a sodium ion battery, aiming to improve the problem of poor cycle performance of sodium-based layered oxide positive electrode materials.

[0004] To achieve the above-mentioned purpose, an embodiment of the present invention proposes a positive electrode material, which is a sodium-based flaky oxide, including an outer wrapping layer and an inner core agglomerate, wherein the inner core agglomerate is embedded in the outer wrapping layer, and the outer wrapping layer at least partially covers the inner core agglomerate; the outer wrapping layer is formed by stacking flaky primary particles, and the inner core agglomerate is formed by interweaving and agglomerating granular primary particles, and the average specific surface area of the flaky primary particles is smaller than the average specific surface area of the granular primary particles.

[0005] In some embodiments, the average specific surface area of the flaky primary particles is S1, the average specific surface area of the granular primary particles is S2, and the ratio of S1 to S2 is greater than 0 and less than or equal to 0.1.

[0006] In some embodiments, the average specific surface area S1 of the flaky primary particles is 0.2 m 2 / g~0.5m 2 / g; and / or, the average specific surface area S2 of the granular primary particles is 1m 2 / g~10m 2 / g.

[0007] In some embodiments, the average length L of the flaky primary particles is 1.5 μm to 10 μm, and the average width W is 0.5 μm to 8 μm; and / or the average particle size R of the granular primary particles is 0.1 μm to 2 μm.

[0008] In some embodiments, the chemical formula of the positive electrode material is Na x Ni aFe b Mn c M d O2, wherein (a+b+c+d)=1, 0.6≤x≤1.0, 0.1≤a≤0.4, 0.1≤b≤0.4, 0.2≤c≤0.8, 0.01≤d≤0.2; M is selected from at least one element of K, Li, Ca, Cu, Mg, Zn, Sr, B, Y, Sn, Al, Nb, Ti, Zr, W, Sr, Co, and Mo; and / or the average particle size Dv50 of the positive electrode material is 6μm to 15μm.

[0009] The present invention also provides a method for preparing a positive electrode material, comprising the following steps:

[0010] A metal salt solution containing a nickel source, an iron source, and a manganese source is prepared, and the metal salt solution is subjected to a coprecipitation reaction to obtain a precursor; the precursor is mixed with a sodium source and an M source and then subjected to a first calcination treatment to obtain a positive electrode material precursor; the positive electrode material precursor is mixed with M 1 After mixing the sources, a second calcination process is performed to obtain the positive electrode material;

[0011] Alternatively, a metal salt solution containing a nickel source, an iron source, a manganese source, and an M source is prepared, and the metal salt solution is subjected to a coprecipitation reaction to obtain a precursor; the precursor is mixed with a sodium source and then subjected to a first sintering treatment to obtain a positive electrode material precursor; the positive electrode material precursor is mixed with M 1 After mixing the sources, a second sintering process is performed to obtain the positive electrode material;

[0012] Wherein, the M source includes at least one of a K source, a Li source, a Ca source, a Cu source, a Mg source, a Zn source, a Sr source, a B source, a Y source, a Sn source, an Al source, a Nb source, a Ti source, a Zr source, a W source, a Sr source, a Co source, and a Mo source,

[0013] The M 1 The source includes at least one of a Cu source, a B source, a Nb source, a W source, a Ti source, and a Ca source; 1 The particle size distribution of the source is 2≤(D90-D10) / D50≤10.

[0014] In some embodiments, the M 1 The particle size parameters of the source are 0.1 μm ≤ D10 ≤ 2 μm, 10 μm ≤ D90 ≤ 100 μm, and 0.8 μm ≤ D50 ≤ 10 μm;

[0015] And / or, the M 1 The mass ratio of the source to the positive electrode material precursor is 1:(20-200);

[0016] And / or, the molar ratio of the sodium element in the sodium source to the nickel element in the nickel source, the iron element in the iron source, the manganese element in the manganese source, and the M element in the M source is (0.6~1):(0.1~0.4):(0.1~0.4):(0.2~0.8):(0.01~0.2).

[0017] In some embodiments, the first sintering treatment is performed for 3 hours to 12 hours at a calcination temperature of 800°C to 950°C; and / or the second sintering treatment is performed for 6 hours to 15 hours at a calcination temperature of 850°C to 1000°C.

[0018] The present invention also provides a positive electrode plate, comprising a current collector and a positive electrode active material layer arranged on at least one surface of the current collector, wherein the positive electrode active material layer comprises the above-mentioned positive electrode material or the positive electrode material prepared by the above-mentioned preparation method.

[0019] An embodiment of the present invention further provides a sodium ion battery, which includes the above-mentioned positive electrode plate.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] The positive electrode material of the present invention presents a structural feature similar to "roujiamo" in its microscopic morphology, that is, a single secondary agglomerate of the positive electrode material is composed of a number of flaky primary particles and core agglomerates, and the core agglomerates are embedded in and aggregated between larger flaky particles. In particles of this morphology, these flaky particles form a stable framework structure inside the material through their flaky morphology and stacking method, which mainly plays the role of limiting the volume expansion of the core agglomerates. At the same time, they can also disperse the stress generated during the charging and discharging process, and avoid structural damage caused by volume changes. The core agglomerates are formed by the interweaving of primary particles with smaller particle sizes, have a higher specific surface area, become the main active part of the material, and undertake most of the electrochemical reaction tasks. These small particle agglomerates are wrapped and fixed by large flaky particles, so that they are constrained during the charging and discharging process, which significantly reduces the volume expansion and stress accumulation.

[0022] Through this design, large flaky particles firmly "sandwich" small particle aggregates, not only fully limiting the volume change of small particle aggregates during cycling, but also significantly alleviating the stress between small particles. This synergistic mechanism improves the material's cycling stability and solves the problem of rapid performance degradation of traditional sodium-based flaky oxide cathode materials during long-term cycling.

[0023] The preparation method of the positive electrode material of the present invention is to add M with a wide particle size distribution during the second sintering. 1The source powder acts as a flux to achieve uneven fluxing on the particles, thereby achieving the coexistence of larger flake particles and smaller particle agglomerates in the same particle. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0025] Figure 1 This is an SEM image of the positive electrode material of Example 1 of the present invention.

[0026] Figure 2 This is an SEM image of the positive electrode material of Comparative Example 1 of the present invention.

[0027] Figure 3 This is an SEM image of the positive electrode material of Comparative Example 2 of the present invention.

[0028] Figure 4 This is an SEM image of the positive electrode material of Comparative Example 3 of the present invention.

[0029] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0031] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0034] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0035] In this application, the term "average specific surface area" is defined as the total surface area per unit mass of particles (m 2 The specific surface area of each particle type is calculated using nitrogen adsorption. At least three independent tests are performed for each particle type, and the arithmetic mean of these test results is calculated as the average specific surface area for that particle type.

[0036] The terms "average length, L" and "average width, W" are used to describe the geometric dimensions of flaky primary particles. "Average length, L" is defined as the longest dimension of a flaky particle, while "average width, W" is defined as the transverse dimension perpendicular to the length. These dimensions are calculated by capturing a topographic image of the particles using a scanning electron microscope, randomly selecting at least 50 particles from the image, and measuring the length and width of each particle using software tools such as Image J. Finally, the arithmetic mean of all the measured data is calculated to determine the average length, L, and average width, W, of the particles.

[0037] The term "average particle size, R," refers to the equivalent spherical diameter of granular primary particles. Its calculation is accomplished using a Malvern 3000 instrument, which measures particle size distribution based on dynamic light scattering and directly provides the Dv50 value, the volume median particle size. The average particle size, R, is determined by measuring at least 100 randomly selected particles and calculating the arithmetic mean of these diameters.

[0038] Sodium-based layered oxides are a class of + ) is a layered positive electrode material with charge carriers, which is widely used in sodium ion batteries. This type of material usually has the general formula Na x TMO2 (where x is the content of sodium ions, and TM represents a transition metal element, such as Mn, Fe, Co, Ni, etc.). With its unique crystal structure and properties, sodium-based layered oxide cathode materials exhibit the following advantages in sodium-ion batteries: sodium resources are abundant and inexpensive, making them more economical than lithium-ion batteries; the transition metal oxide layer provides abundant active sites, which can achieve a higher theoretical specific capacity, thereby meeting the needs of high-performance energy storage. However, this type of material also has some challenges. During the charge and discharge process, the repeated insertion and deinsertion of sodium ions will cause significant volume expansion and contraction of the positive electrode material. This volume change will trigger the accumulation of stress inside the material, which will lead to particle breakage, pulverization or structural collapse, thereby affecting the structural stability and cycle life of the material.

[0039] Based on this, an embodiment of the present invention proposes a positive electrode material, which is a sodium-based flaky oxide, including an outer wrapping layer and an inner core agglomerate, the inner core agglomerate is embedded in the outer wrapping layer, and the outer wrapping layer at least partially covers the inner core agglomerate; the outer wrapping layer is formed by stacking flaky primary particles, and the inner core agglomerate is formed by interweaving and agglomerating granular primary particles, and the average specific surface area of the flaky primary particles is smaller than the average specific surface area of the granular primary particles.

[0040] See also Figure 1In one embodiment of the present invention, the positive electrode material consists of two components: an outer coating and inner core aggregates. The inner core aggregates are embedded within the outer coating, which at least partially covers them. This structure is similar to a "roujiamo" (a type of steamed bun), with the outer coating representing the "mochi" and the inner core aggregates representing the "meat." The outer coating is composed of stacked flaky primary particles. These flaky primary particles have a large average length, forming a relatively stable framework that provides support and protection. The inner core aggregates are composed of smaller granular primary particles that are interwoven and aggregated. These granular primary particles have a small average particle size and a high specific surface area, making them the primary active component of the material and responsible for participating in electrochemical reactions. The large flaky particles primarily limit the volume expansion of the inner core aggregates, dissipating the stress generated during charge and discharge, and protecting them from mechanical damage. The inner core aggregates, composed of smaller particles, are the primary active component of the material, carrying out the majority of the electrochemical reactions. Because they are immobilized by the outer coating, volume changes and stress accumulation are reduced.

[0041] The technical solution of the present invention not only optimizes the mechanical stability and electrochemical properties of the material by adopting this design, but also solves the performance degradation problem of traditional sodium-based layered oxide positive electrode materials caused by volume expansion and stress accumulation during the cycle.

[0042] In some embodiments, the average specific surface area of the flaky primary particles is S1, and the average specific surface area of the granular primary particles is S2. The ratio of S1 to S2 is greater than 0 and less than or equal to 0.1. Specific surface area refers to the total area per unit mass of a material. A larger specific surface area indicates a greater number of surface active sites. S1 / S2 ≤ 0.1 indicates that the specific surface area of the flaky primary particles is much smaller than that of the granular primary particles. Due to their larger size and lower specific surface area, flaky particles exhibit lower electrochemical activity. They primarily provide mechanical support, forming a stable framework that limits the volume expansion of the core aggregates during charge and discharge. Granular particles have a higher specific surface area, providing more active sites and shouldering the majority of the electrochemical reaction load. This enables the material to achieve higher capacity utilization during charge and discharge. By rationally designing the specific surface area ratio of flaky and granular primary particles, an optimal balance can be found between structural stability and electrochemical performance. The flaky particles provide mechanical support, while the granular particles contribute the majority of the electrochemical activity. The two work synergistically to enhance the overall performance of the material.

[0043] In some embodiments, the average specific surface area S1 of the flaky primary particles is 0.2 m 2 / g~0.5m 2 / g. Due to their larger size, large flaky primary particles usually have a smaller specific surface area.

[0044] In some embodiments, the average specific surface area S2 of the granular primary particles is 1 m 2 / g~10m 2 / g. Specific surface area refers to the total surface area per unit mass of material (unit: m 2 For cathode materials, specific surface area directly affects their contact area with the electrolyte, thus affecting the electrochemical reaction. Granular primary particles have a higher specific surface area and can provide more active sites.

[0045] In some embodiments, the average length L of the flaky primary particles is 1.5 μm to 10 μm, and the average width W is 0.5 μm to 8 μm. The length and width of the flaky particles can be directly measured by observing the morphology of the flaky particles using a scanning electron microscope or the like. Flaky primary particles are particles with a flat morphology, and their geometry can be described by length and width. "Average length" refers to the main dimension of the flaky particles in the extension direction. The average length L of the flaky primary particles is between 1.5 μm and 10 μm. As an example, the average length L can be typical but non-limiting values such as 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm. A longer length helps to form a more stable stacking structure, thereby enhancing the mechanical strength of the outer coating and the limiting effect on the inner core agglomerates. The average width W of the flaky primary particles is between 0.5 μm and 8 μm. As an example, the average width W can be typical but non-limiting values such as 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, and 8 μm. The width and length together determine the planar surface area of the flaky particles. A larger surface area can better cover and protect the core aggregates. Flaky primary particles with the above size range can better form an outer coating and provide mechanical support for the core aggregates. The larger length and moderate width enable these particles to form a stable framework structure when stacked.

[0046] In some embodiments, the average particle size R of the granular primary particles is 0.1 μm to 2 μm. The "particle size" here refers to the equivalent diameter of the particles (for example, the diameter when the particles are spherical), which is used to describe the size of the particles. The morphology of the granular primary particles can be rod-shaped, spherical, quasi-spherical, flake-shaped, linear, etc. As an example, the average particle size R can be typical but non-limiting values such as 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2 μm, etc. Within the above particle size range, the particle size of the granular primary particles is small and moderate, which can provide a larger specific surface area, thereby increasing the active sites of the electrochemical reaction and improving the specific capacity and rate performance of the material. This moderate size range helps to strike a balance between high specific surface area and good structural stability.

[0047] In some embodiments, the chemical formula of the positive electrode material is Na x Ni a Fe b Mn c M d O2, wherein (a+b+c+d)=1, 0.6≤x≤1.0, 0.1≤a≤0.4, 0.1≤b≤0.4, 0.2≤c≤0.8, 0.01≤d≤0.2; and M is selected from at least one of K, Li, Ca, Cu, Mg, Zn, Sr, B, Y, Sn, Al, Nb, Ti, Zr, W, Sr, Co, and Mo.

[0048] The general chemical formula of the sodium-based layered oxide cathode material shows that it is composed of elements such as sodium, nickel, iron, manganese, and M. Here, x, a, b, c, and d are the molar ratio coefficients of each element, and they satisfy the sum condition: (a+b+c+d)=1. Adjusting the value of x can change the insertion / extraction ability of sodium ions, and adjusting the ratio of Ni, Fe, and Mn can balance the energy density and stability of the material. The introduction of the doping element M further optimizes the crystal structure of the material, thereby improving the material's cycling stability.

[0049] In some embodiments, the average particle size Dv50 of the positive electrode material is 6μm to 15μm. Dv50 is used to describe the particle size distribution of the material, which represents the particle size value when the total count of particles in a sample reaches 50%. It usually refers to 50% of the powder particles larger and smaller than the particle size. As an example, the Dv50 particle size of the positive electrode material can be typical but non-limiting values such as 6μm, 7μm, 8μm, 9μm, 10μm, 12μm, 14μm, and 15μm. The particle size of the positive electrode material has an important influence on the performance of the battery. The positive electrode material of the present application has a suitable particle size range, which can better improve the energy density and power density of the sodium ion battery, thereby improving the cycle life of the battery.

[0050] The present invention also provides a method for preparing a positive electrode material, comprising the following steps:

[0051] A metal salt solution containing a nickel source, an iron source, and a manganese source is prepared, and the metal salt solution is subjected to a coprecipitation reaction to obtain a precursor; the precursor is mixed with a sodium source and a M source and then subjected to a first calcination treatment to obtain a positive electrode material precursor; the positive electrode material precursor is mixed with M 1 After the sources are mixed, a second calcination process is performed to obtain the positive electrode material.

[0052] In some other embodiments, a method for preparing a positive electrode material is also provided, comprising the following steps:

[0053] A metal salt solution containing a nickel source, an iron source, a manganese source and an M source is prepared, and the metal salt solution is subjected to a coprecipitation reaction to obtain a precursor; the precursor is mixed with a sodium source and then subjected to a first sintering treatment to obtain a positive electrode material precursor; the positive electrode material precursor is mixed with M 1 The sources are mixed and then subjected to a second sintering process to obtain the positive electrode material.

[0054] In the embodiments of the present application, the nickel source, manganese source, and iron source are independently selected from any one or more combinations of sulfates, hydrochlorides, nitrates, carbonates, acetates, oxides, sulfides, nitrides, and hydroxides of the corresponding metal ions. The sodium source includes any one or more combinations of anhydrous sodium carbonate, sodium carbonate monohydrate, sodium carbonate decahydrate, sodium bicarbonate, and sodium sulfate. Mixing can be performed using a mixing device such as a mixer, a high-pressure mixer, or a ball mill.

[0055] In the above two methods for preparing the positive electrode material, the M source includes at least one of a K source, a Li source, a Ca source, a Cu source, a Mg source, a Zn source, a Sr source, a B source, a Y source, a Sn source, an Al source, a Nb source, a Ti source, a Zr source, a W source, a Sr source, a Co source, and a Mo source. As an example, the M source is selected from sulfates, hydrochlorides, nitrates, carbonates, acetates, oxides, sulfides, nitrides, or hydroxides corresponding to any one or more combinations of K, Li, Ca, Cu, Mg, Zn, Sr, B, Y, Sn, Al, Nb, Ti, Zr, W, Sr, Co, and Mo.

[0056] Among them, M 1 The source includes at least one of a Cu source, a B source, a Nb source, a W source, a Ti source, and a Ca source. Elemental sources such as Cu, B, Nb, W, Ti, and Ca have strong fluxing abilities and moderate chemical activity, and are therefore more suitable for achieving a non-uniform fluxing effect.

[0057] M 1 The particle size distribution of the source is 2≤(D90-D10) / D50≤10. The particle size distribution parameters (D10, D50, D90) are key indicators in the statistical analysis of the material particle size. D10 indicates that 10% of the particles in the cumulative particle size distribution curve are smaller than this value; D50 indicates that 50% of the particles in the cumulative particle size distribution curve are smaller than this value (i.e., the median particle size); and D90 indicates that 90% of the particles in the cumulative particle size distribution curve are smaller than this value.

[0058] (D90-D10) / D50 is a dimensionless ratio used to measure the width or uniformity of a particle size distribution. (D90-D10) represents the span of the particle size distribution, i.e., the range of particle sizes covered by 10% to 90% of the particles. Therefore, a smaller (D90-D10) / D50 value indicates a more concentrated particle size distribution; conversely, a larger value indicates a broader particle size distribution. A range of 2 ≤ (D90-D10) / D50 ≤ 10 indicates that the particle size distribution is neither too concentrated (e.g., near-monodisperse) nor too broad (e.g., multimodal), but rather falls within a moderate range.

[0059] M 1 The particle size parameters of the source are 0.1μm≤D10≤2μm, 10μm≤D90≤100μm, 0.8μm≤D50≤10μm. This particle size parameter range indicates that M 1 The upper limit of small particles in the source powder is ≤2μm, M 1 The lower limit of large particles in the source powder is ≥10 μm, which means that M 1The source powder has a wide particle size distribution, that is, its particle size ranges from very fine (≤2μm) to relatively large (≥10μm). Among them, fine particles are more easily dispersed to the surface of the cathode material precursor, forming local high concentration areas. Due to their smaller size, they can penetrate deeper into the micropores or defects on the particle surface, thereby producing a stronger flux effect at these locations, resulting in strong melting and grain growth, forming larger flaky particles. Larger particles are more difficult to disperse evenly and are usually concentrated in certain specific areas. Their presence will result in a lower degree of local melting, retaining smaller agglomerate particles. This will form an uneven flux effect on the surface of the cathode material particles. Therefore, M 1 The wide particle size distribution of the source powder results in uneven distribution and action of the flux on the surface of the positive electrode material particles, thereby achieving the effect of simultaneously forming larger flake particles and smaller agglomerate particles in the same particle during the sintering process.

[0060] The positive electrode material of the embodiment of the present invention can be prepared by a co-precipitation method plus a high-temperature solid phase method. The positive electrode material Na designed in this application x Ni a Fe b Mn c M d The atomic ratio of O2 is used to calculate the appropriate molar ratio of Na, Ni, Fe, Mn, and M, and then converted into the mass of Na source, Ni source, Fe source, Mn source, and M source, and the corresponding mass of material is weighed. First, Ni source, Fe source, and Mn source are used as raw materials, and a co-precipitation method is adopted to prepare a nickel-manganese-iron ternary precursor. Alternatively, Ni source, Fe source, Mn source, and M source can be used as raw materials, and a co-precipitation method is adopted to prepare a precursor containing Ni, Fe, Mn, and M. The co-precipitation method can adopt the method in the prior art, which will not be described here. The nickel-manganese-iron ternary precursor is then mixed with a sodium source and an M source, or the precursor containing Ni, Fe, Mn, and M is mixed with a sodium source, and then sintered together to allow the precursor material particles to combine with each other to form a positive electrode material precursor. Then, by adding M with a wide particle size distribution to the positive electrode material precursor during the second sintering process, 1 The source powder acts as a flux, achieving a non-uniform fluxing effect on the particle surface. This method can simultaneously form larger flake-like particles and smaller agglomerated particles within the same particle. This preparation process is simple and easy to implement, making it well-suited for large-scale industrial production.

[0061] In some embodiments, M 1The mass ratio of the source to the cathode material precursor is 1:(20-200). As examples, the mass ratio of the two can be 1:20, 1:50, 1:80, 1:120, 1:140, 1:170, 1:200, and other typical but non-limiting values. When the mass ratio of the two is within the above range, the performance of the prepared cathode material can be improved.

[0062] In some embodiments, the molar ratio of the sodium element in the sodium source to the nickel element in the nickel source, the iron element in the iron source, the manganese element in the manganese source, and the M element in the M source is (0.6-1):(0.1-0.4):(0.1-0.4):(0.2-0.8):(0.01-0.2).

[0063] In some embodiments, the first sintering treatment lasts for 3 to 12 hours, and the calcination temperature is 800°C to 950°C. In some embodiments, the second sintering treatment lasts for 6 to 15 hours, and the calcination temperature is 850°C to 1000°C. By way of example, the first calcination temperature may be 800°C, 850°C, 870°C, 900°C, 920°C, 940°C, 950°C, and other typical but non-limiting values; the second calcination temperature may be 850°C, 870°C, 900°C, 920°C, 940°C, 960°C, 980°C, 1000°C, and other typical but non-limiting values. The first calcination time may be 3 hours, 6 hours, 7 hours, 8 hours, 9 hours, 11 hours, 12 hours, and other typical but non-limiting values. The second calcination time may be 6 hours, 7 hours, 8 hours, 9 hours, 11 hours, 13 hours, 15 hours, and other typical but non-limiting values. The sintering process of the embodiment of the present application can be carried out in an inert gas atmosphere. Inert gases include but are not limited to at least one of nitrogen, argon, and helium. As an example: the inert gas can be selected from argon, and the gas flow rate can be 5L / min. The sintering temperature has an important influence on the structure and electrochemical properties of the positive electrode material. If the sintering temperature is too low, the positive electrode material with a roujiamo morphology structure cannot be prepared. If the sintering temperature is too high, it may cause the stability and cycle life of the positive electrode material to be reduced. By controlling the sintering temperature within the above range, a positive electrode material having the structural characteristics of the present invention and good electrochemical properties can be prepared.

[0064] On the other hand, an embodiment of the present invention further provides a positive electrode plate, comprising a current collector and a positive electrode active material layer arranged on at least one surface of the current collector, wherein the positive electrode active material layer comprises the above-mentioned positive electrode material or the positive electrode material prepared by the above-mentioned preparation method.

[0065] On the other hand, an embodiment of the present invention further provides a sodium ion battery, which includes the above-mentioned positive electrode plate.

[0066] The following describes the details in conjunction with specific embodiments.

[0067] Example 1

[0068] This embodiment provides a positive electrode material, the chemical formula of which is Na 0.7 Ni 0.2 Fe 0.2 Mn 0.4 Cu 0.2 The preparation method of the positive electrode material comprises the following steps:

[0069] S1: A spherical hydroxide precursor with a ratio of Ni:Fe:Mn=1:1:2 was prepared by coprecipitation.

[0070] S2: The precursor, sodium carbonate, and copper oxide were weighed as raw materials at a molar ratio of Na:Ni:Fe:Mn:Cu of 0.7:0.2:0.2:0.4:0.2. Half the weight of the copper oxide was mixed evenly with the precursor and sodium carbonate in a planetary ball mill. The mixture was then sintered in a box furnace at 830°C for 8 hours. The mixture was then cooled to room temperature and crushed to obtain a cathode material precursor.

[0071] S3: Add the remaining half of the weight of copper oxide (particle size parameters D10 = 0.8 μm, D50 = 2.5 μm, D90 = 15.6 μm) to the cathode material precursor, remix, heat to 900 ° C and sinter for 12 h, perform the second sintering treatment, and finally cool naturally to obtain a cathode material with a roujiamo morphology (see Figure 1 ).

[0072] Example 2

[0073] This embodiment provides a positive electrode material, the chemical formula of which is Na 0.8 Ni 0.15 Fe 0.3 Mn 0.45 Cu 0.1 The preparation method of the positive electrode material comprises the following steps:

[0074] S1: A spherical hydroxide precursor with a ratio of Ni:Fe:Mn=1:2:3 was prepared by coprecipitation.

[0075] S2: The precursor, sodium carbonate, and copper oxide were weighed as raw materials at a molar ratio of Na:Ni:Fe:Mn:Cu of 0.8:0.15:0.3:0.45:0.1. Half the weight of the copper oxide was mixed evenly with the precursor and sodium carbonate in a planetary ball mill. The mixture was then sintered in a box furnace at 850°C for 8 hours. The mixture was then cooled to room temperature and crushed to obtain a cathode material precursor.

[0076] S3: Add the remaining half weight of copper oxide (particle size parameters D10 = 0.8 μm, D50 = 2.5 μm, D90 = 15.6 μm) to the positive electrode material precursor, remix, heat to 900 ° C and sinter for 8 hours, perform the second sintering treatment, and finally cool naturally to obtain a positive electrode material with a roujiamo morphology.

[0077] Example 3

[0078] This embodiment provides a positive electrode material, the chemical formula of which is Na 0.75 Ni 0.24 Fe 0.24 Mn 0.36 Zn 0.1 Nb 0.06 The preparation method of the positive electrode material comprises the following steps:

[0079] S1: A spherical hydroxide precursor with a ratio of Ni:Fe:Mn=2:2:3 was prepared by coprecipitation.

[0080] S2: The precursor, sodium carbonate, zinc oxide, and niobium oxide were weighed as raw materials according to the molar ratio of Na:Ni:Fe:Mn:Zn:Nb of 0.75:0.24:0.24:0.36:0.1:0.06. The precursor, sodium carbonate, and zinc oxide were mixed uniformly in a planetary ball mill and then sintered in a box furnace at 900°C for 6 hours. The mixture was then naturally cooled to room temperature and crushed to obtain a positive electrode material precursor.

[0081] S3: Add niobium oxide (particle size parameters D10 = 0.4 μm, D50 = 1.3 μm, D90 = 9.9 μm) to the positive electrode material precursor, remix, heat to 950°C and sinter for 14 hours, perform a second sintering treatment, and finally cool naturally to obtain a positive electrode material with a roujiamo morphology.

[0082] Example 4

[0083] This embodiment provides a positive electrode material, the chemical formula of which is Na 0.9 Ni 0.2 Fe 0.2 Mn 0.5 Ca 0.05 Nb 0.05 The preparation method of the positive electrode material comprises the following steps:

[0084] S1: A spherical hydroxide precursor with Ni:Fe:Mn:Ca=2:2:5:0.5 was prepared by coprecipitation method;

[0085] S2: The precursor, sodium carbonate, and niobium oxide were weighed as raw materials at a molar ratio of Na:Ni:Fe:Mn:Ca:Nb of 0.9:0.2:0.2:0.5:0.05:0.05. The precursor and sodium carbonate were mixed uniformly in a planetary ball mill and then sintered in a box furnace at 900°C for 6 hours. The mixture was then naturally cooled to room temperature and crushed to obtain a cathode material precursor.

[0086] S3: Add niobium oxide (particle size parameters D10 = 0.4 μm, D50 = 1.3 μm, D90 = 9.9 μm) to the positive electrode material precursor, remix, heat to 950°C and sinter for 14 hours, perform a second sintering treatment, and finally cool naturally to obtain a positive electrode material with a roujiamo morphology.

[0087] Example 5

[0088] This embodiment provides a positive electrode material, the chemical formula of which is Na 0.9 Ni 0.2 Fe 0.2 Mn 0.4 Ti 0.1 Cu 0.08 Nb 0.02 The preparation method of the positive electrode material comprises the following steps:

[0089] S1: A spherical hydroxide precursor with a ratio of Ni:Fe:Mn:Ti:Cu = 2:2:4:1:0.8 was prepared by co-precipitation method;

[0090] S2: The precursor, sodium carbonate, and niobium oxide were weighed as raw materials at a molar ratio of Na:Ni:Fe:Mn:Ti:Cu of 0.9:0.2:0.2:0.4:0.08:0.02. The precursor and sodium carbonate were mixed evenly in a planetary ball mill and then sintered in a box furnace at 900°C for 10 hours. The mixture was then naturally cooled to room temperature and crushed to obtain a cathode material precursor.

[0091] S3: Add niobium oxide (particle size parameters D10 = 0.4 μm, D50 = 1.3 μm, D90 = 9.9 μm) to the positive electrode material precursor, remix, heat to 950°C and sinter for 12 hours, perform a second sintering treatment, and finally cool naturally to obtain a positive electrode material with a roujiamo morphology.

[0092] Example 6

[0093] This embodiment provides a positive electrode material, the chemical formula of which is Na 0.9 Ni 0.33 Fe 0.33 Mn 0.33 Cu 0.01The preparation method of the positive electrode material comprises the following steps:

[0094] S1: A spherical hydroxide precursor with Ni:Fe:Mn=0.33:0.33:0.33 was prepared by coprecipitation method;

[0095] S2: The precursor, sodium carbonate, and titanium oxide were weighed as raw materials at a molar ratio of Na:Ni:Fe:Mn of 0.9:0.33:0.33:0.33. The precursor and sodium carbonate were mixed evenly in a planetary ball mill and then sintered in a box furnace at 900°C for 10 hours. The mixture was then naturally cooled to room temperature and crushed to obtain a cathode material precursor.

[0096] S3: Add copper oxide (particle size parameters D10 = 0.8 μm, D50 = 2.5 μm, D90 = 15.6 μm) to the positive electrode material precursor, remix, heat to 950 ° C and sinter for 12 hours, perform the second sintering treatment, and finally cool naturally to obtain a positive electrode material with a roujiamo morphology.

[0097] Comparative Example 1

[0098] The difference between the preparation method of the positive electrode material of Comparative Example 1 and that of Example 1 is that: the M 1 The particle size of the source (copper oxide) satisfies the particle size parameters D10 = 1.5 μm, D50 = 3.9 μm, D90 = 7.6 μm).

[0099] The cathode material of comparative example 1 does not have a special meat-and-steamed bun morphology, which is mainly due to the addition of M 1 The source particle size is relatively uniform, and its melting effect results in a small difference in the primary particle size of the sample, which cannot form a special Roujiamo morphology, such as Figure 2 As shown, the positive electrode material is directly stacked by primary particles of similar size, and there is no obvious stratification or wrapping relationship between the particles.

[0100] Comparative Example 2

[0101] The difference between the preparation method of the positive electrode material of Comparative Example 2 and that of Example 2 is that: the M 1 The particle size of the source (copper oxide) satisfies the particle size parameters D10 = 0.7 μm, D50 = 10.5 μm, and D90 = 112.2 μm).

[0102] The cathode material of Comparative Example 2 does not have a special meat-and-steamed bun morphology, and there is obviously unreacted M1 source, which is mainly due to the addition of M 1 The source particle size distribution is too uneven and D90 is too large, resulting in insufficient sintering and the inability to form a finished product material with uniform composition and Roujiamo morphology, such as Figure 3As shown, the particles of the positive electrode material are irregular, and there are obviously raw material particles that are not completely sintered.

[0103] Comparative Example 3

[0104] The preparation method of the positive electrode material of Comparative Example 3 is different from that of Example 3 in that zinc oxide is added as a flux in the second sintering stage.

[0105] The cathode material of Comparative Example 3 does not have a special meat-and-mo morphology, which is mainly due to the poor melting effect of zinc oxide, which cannot form a special meat-and-mo morphology. Figure 4 As shown, all particles of the positive electrode material have similar particle sizes and do not form a structure of "small particle core and large particle outer layer".

[0106] Comparative Example 4

[0107] The difference between the preparation method of the positive electrode material of Comparative Example 4 and that of Example 4 is that the M 1 In step 1, a spherical hydroxide precursor with a ratio of Ni:Fe:Mn:Ca=2:2:5:1 is prepared by co-precipitation.

[0108] The cathode material of Comparative Example 4 does not have a special meat-and-steamed bun morphology, which is mainly due to the absence of M 1 The source acts as a flux, resulting in the sample being unable to form the special roujiamo morphology.

[0109] Comparative Example 5

[0110] The preparation method of the positive electrode material of Comparative Example 5 differs from that of Example 5 in that a weighed sample of sodium carbonate, ferric oxide, manganese oxide, titanium oxide, and copper oxide in a Na:Ni:Fe:Mn:Ti:Cu ratio of 0.9:0.2:0.2:0.4:0.1:0.1 was used as raw materials and directly subjected to the first and second stages of sintering. A quasi-spherical hydroxide precursor prepared by coprecipitation with a Ni:Fe:Mn:Ti:Cu ratio of 2:2:4:1:1 was not used. The positive electrode material of Comparative Example 5 did not have the distinctive meat-and-mom morphology. This is mainly because the positive electrode material formed by sintering pure oxides has a poor morphology and cannot form the distinctive meat-and-mom morphology.

[0111] Material performance testing

[0112] In order to verify the progress of the examples of the present application, the samples of the examples and comparative examples were tested as follows:

[0113] 1. Scanning electron microscopy (SEM)

[0114] A scanning electron microscope (SEM) uses an electron beam to scan the surface of a sample to obtain information about the surface morphology of the material. When the electron beam bombards the surface of the sample, the interaction with the material will produce secondary electrons and scattered electrons, which will be further processed into corresponding morphological images. The SEM resolution is around 2nm. Through SEM testing, the microscopic morphology and structure of the material can be deeply and meticulously analyzed, and the morphology of the positive electrode material can be characterized. This application uses a Japanese Hitachi (Hitachi S-4800) scanning electron microscope to characterize and test the material morphology.

[0115] 2. Average particle size D V 50 tests

[0116] Equipment model: Malvern 3000 (MasterSizer 2000) laser particle size analyzer, reference standard process: GB / T19077-2016 / ISO 13320:2009, specific test process: Take an appropriate amount of the sample to be tested (the sample concentration is sufficient to ensure 8-12% obscuration), add 20ml of NMP, and simultaneously ultraviolet (53KHz / 120W) for 5 minutes to ensure that the sample is completely dispersed. Then, the sample is measured according to GB / T19077-2016 / ISO 13320:2009 standard.

[0117] 3. Specific surface area test

[0118] After the sintered material is cooled to room temperature, it is screened using a vibrating screen with a mesh size of 300. The vibrating screen is started and closed after the material is screened. Large flaky primary particles remain on the screen, and small primary particles pass through the screen, indicating successful screening. The two materials are collected and sent for specific surface area measurement. Micromeritics 3030 model equipment is used, using nitrogen adsorption method based on Brunauer-Emmett-Teller (BET) theory to obtain the specific surface area parameters of the two materials.

[0119] 4. Elemental analysis test

[0120] The sodium and metal element content in the cathode material was measured using an inductively coupled plasma spectrometer (ICP, PE Optima 7000DV). An appropriate amount of powder sample was weighed, and approximately 10 mL of aqua regia was added. The sample was heated on a flat-plate heating device at approximately 185°C for 30 to 50 minutes to fully digest the sample before testing.

[0121] 5. Positive electrode thickness test

[0122] Use a digital micrometer or thickness gauge with an accuracy of 1μm, select at least 5 evenly distributed measuring points on the surface of the electrode (avoid the edges and uneven coating areas), and gently apply standard pressure (usually 20-50g / cm2) to ensure smooth contact; record the thickness value of each measuring point, and calculate the average value as the electrode thickness. The test must be carried out in a constant temperature and humidity environment (such as temperature 23℃±2℃, humidity 50%±5%).

[0123] Battery performance test

[0124] The positive electrode materials prepared in the above examples and comparative examples were mixed with a conductive agent (conductive carbon black) and a binder (polyvinylidene fluoride (PVDF)) at a weight ratio of 90:5:5, applied uniformly to aluminum foil to form an electrode sheet, and then vacuum-dried. 12.5% NaPF6 sodium salt was dissolved in diglyme (DIGLYME) and stirred uniformly. This electrolyte was then assembled into CR2032 button-type batteries in an argon atmosphere glove box (H2O <0.1ppm, O2 <0.1ppm) for testing.

[0125] 1. Specific capacity test

[0126] The battery was charged and discharged at a rate of 0.1C over a voltage range of 2.0V to 4.0V. The battery was then charged to 4.0V at a constant current and maintained at a constant voltage until the current decayed to 0.05C. The battery was then discharged from 4.0V to 2.0V at the same rate, and the discharge capacity Q (in mAh) was recorded throughout the process. Simultaneously, the mass m (in g) of the active material in the battery was measured, and the specific capacity (in mAh / g) was calculated using the formula specific capacity = Q / m.

[0127] 2. Battery capacity retention test

[0128] The battery capacity retention test process is as follows: At 25°C, the battery is charged to 4.8V at a current density of 20mA / g, then discharged to 2.0V at a current density of 20mA / g to obtain the discharge specific capacity C0 of the button battery. Subsequently, the battery is charged and discharged at a current density of 20mA / g for 100 cycles, and the discharge specific capacity C1 of the 100th cycle is obtained. The capacity retention rate of the positive electrode active material after 100 cycles = (C1 / C0) × 100%. The battery capacity retention rate data corresponding to Example 1 in Table 1 is the data measured after 100 cycles under the above test conditions. The testing process for the comparative example and other examples is the same as above.

[0129] 3.10C / 1C capacity retention rate test

[0130] The battery was discharged at a constant current of 1C to a termination voltage of 2.5V, and the discharge capacity Q was recorded. 1C; Then fully charge the battery again, and then discharge it at a constant current of 10C to the same end voltage of 2.5V, and record the discharge capacity Q 10C ;Finally, according to the formula:

[0131] Capacity retention rate = Q 10C / Q 1C ×100% to calculate the capacity retention rate and evaluate the performance of the battery under high rate conditions.

[0132] Performance Results

[0133] Figure 1 This is the SEM morphology of the positive electrode material of Example 1. It can be seen from the figure that the single secondary particle of the positive electrode material is composed of several larger flaky primary particles and multiple smaller small particle agglomerates, and the small particle agglomerates are gathered between the larger flaky particles, forming a unique "roujiamo" morphology.

[0134] Table 1 and Table 2 are the characterization data tables of the positive electrode materials obtained in Examples 1-5 and Comparative Examples 1-5. Figures 2 to 4 No distinction is made between several larger flaky primary particles and multiple smaller particles, and the specific surface area S1 or S2, average length L, average width W and average particle size R defined in this application do not exist. Therefore, the average specific surface area, average length, average width and average particle size of the positive electrode materials obtained in Comparative Examples 1-5 are not further measured.

[0135] Table 1

[0136]

[0137] Table 2

[0138]

[0139] As can be seen from the data in Table 2, the specific capacities of the Examples are generally higher than or equal to those of the Comparative Examples. For example, the specific capacity of Example 1 is 123 mAh / g, while the specific capacity of Comparative Example 1 is only 115 mAh / g. This indicates that the energy density of the Examples is higher.

[0140] The capacity retention of the examples is significantly better than that of the comparative examples. For example, the 100th capacity retention of Example 1 is 96.3%, while that of Comparative Example 1 is only 88.2%. Compared with the comparative examples, the examples perform better in cycle life (100th capacity retention), demonstrating better stability and durability.

[0141] The electrode sheets of the examples show minimal change in thickness after 100 charge-discharge cycles, demonstrating superior structural stability. For example, the initial thickness of Example 1 was 0.197 mm, and after 100 charge-discharge cycles it was 0.199 mm, showing minimal change. In contrast, the initial thickness of Comparative Example 1 was 0.189 mm, and after 100 charge-discharge cycles it was 0.204 mm, showing a significant change. These results demonstrate that, compared to the comparative example, the examples exhibit greater structural stability and are less susceptible to expansion during multiple charge-discharge cycles.

[0142] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformation made by utilizing the contents of the present invention's description and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A positive electrode material, characterized in that The positive electrode material is a sodium-based layered oxide, comprising an outer wrapping layer and an inner core agglomerate, wherein the inner core agglomerate is embedded in the outer wrapping layer, and the outer wrapping layer at least partially covers the inner core agglomerate; The outer coating layer is formed by stacking flaky primary particles, the inner core agglomerates are formed by interweaving and agglomerating granular primary particles, and the average specific surface area of the flaky primary particles is smaller than the average specific surface area of the granular primary particles.

2. The positive electrode material according to claim 1, wherein The average specific surface area of the flaky primary particles is S1, the average specific surface area of the granular primary particles is S2, and the ratio of S1 to S2 is greater than 0 and less than or equal to 0.

1.

3. The positive electrode material according to claim 2, wherein The average specific surface area S1 of the flaky primary particles is 0.2 m 2 / g~0.5m 2 / g; and / or, the average specific surface area S2 of the granular primary particles is 1m 2 / g~10m 2 / g.

4. The positive electrode material according to claim 1, wherein The average length L of the flaky primary particles is 1.5 μm to 10 μm, and the average width W is 0.5 μm to 8 μm; and / or the average particle size R of the granular primary particles is 0.1 μm to 2 μm.

5. The positive electrode material according to any one of claims 1 to 4, characterized in that The chemical formula of the positive electrode material is Na x Ni a Fe b Mn c M d O2, wherein (a+b+c+d)=1, 0.6≤x≤1.0, 0.1≤a≤0.4, 0.1≤b≤0.4, 0.2≤c≤0.8, 0.01≤d≤0.2; M includes at least one element selected from K, Li, Ca, Cu, Mg, Zn, Sr, B, Y, Sn, Al, Nb, Ti, Zr, W, Sr, Co, and Mo; and / or the average particle size Dv50 of the positive electrode material is 6 μm to 15 μm.

6. A method for preparing a positive electrode material, characterized in that: The following steps are involved: A metal salt solution containing a nickel source, an iron source, and a manganese source is prepared, and the metal salt solution is subjected to a coprecipitation reaction to obtain a precursor; the precursor is mixed with a sodium source and an M source and then subjected to a first calcination treatment to obtain a positive electrode material precursor; the positive electrode material precursor is mixed with M 1 After mixing the sources, a second calcination process is performed to obtain the positive electrode material; Alternatively, a metal salt solution containing a nickel source, an iron source, a manganese source, and an M source is prepared, and the metal salt solution is subjected to a coprecipitation reaction to obtain a precursor; the precursor is mixed with a sodium source and then subjected to a first sintering treatment to obtain a positive electrode material precursor; the positive electrode material precursor is mixed with M 1 After mixing the sources, a second sintering process is performed to obtain the positive electrode material; Wherein, the M source includes at least one of a K source, a Li source, a Ca source, a Cu source, a Mg source, a Zn source, a Sr source, a B source, a Y source, a Sn source, an Al source, a Nb source, a Ti source, a Zr source, a W source, a Sr source, a Co source, and a Mo source, The M 1 The source includes at least one of a Cu source, a B source, a Nb source, a W source, a Ti source, and a Ca source; 1 The particle size distribution of the source is 2≤(D90-D10) / D50≤10.

7. The method for preparing the positive electrode material according to claim 6, wherein: The M 1 The particle size parameters of the source are 0.1 μm ≤ D10 ≤ 2 μm, 10 μm ≤ D90 ≤ 100 μm, and 0.8 μm ≤ D50 ≤ 10 μm; And / or, the M 1 The mass ratio of the source to the positive electrode material precursor is 1:(20-200); And / or, the molar ratio of the sodium element in the sodium source, the nickel element in the nickel source, the iron element in the iron source, the manganese element in the manganese source, and the M element in the M source is (0.6~1):(0.1~0.4):(0.1~0.4):(0.2~0.8):(0.01~0.2).

8. The method for preparing the positive electrode material according to claim 6 or 7, wherein: The first sintering treatment lasts for 3 hours to 12 hours, and the calcination temperature is 800° C. to 950° C.; and / or, The second sintering treatment lasts for 6 hours to 15 hours, and the calcination temperature is 850° C. to 1000° C.

9. A positive electrode plate, characterized in that: The invention comprises a current collector and a positive electrode active material layer arranged on at least one surface of the current collector, wherein the positive electrode active material layer comprises the positive electrode material according to any one of claims 1 to 5 or the positive electrode material prepared by the preparation method according to any one of claims 6 to 8.

10. A sodium ion battery, characterized in that: The sodium ion battery comprises the positive electrode sheet according to claim 9.

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