Positive electrode active material, method for preparing the same, and battery

Abstract

The application provides a positive electrode active material, a preparation method thereof and a battery. The positive electrode active material comprises first active particles and second active particles, the average particle size of the first active particles is smaller than that of the second active particles; the first active particles have a first peak and the second active particles have a second peak on a particle size distribution curve of the positive electrode active material, and the ratio r1 of the numerical value of the peak top of the first peak to that of the peak top of the second peak ranges from 0.3 to 0.8.

Description

Technical Field

[0001] This application relates to the field of energy storage, specifically to a positive electrode active material, its preparation method, and a battery. Background Technology

[0002] Sodium iron pyrophosphate (Na4Fe3(PO4)2(P2O7), with its three-dimensional sodium ion diffusion channels and sodium superionic conductor structure, exhibits high voltage plateau, high capacity, excellent rate capability, and excellent cycle stability, making it a promising cathode material for large-scale production in sodium-ion batteries. However, the current compaction density of Na4Fe3(PO4)2(P2O7) remains relatively low. Summary of the Invention

[0003] This application provides a positive electrode active material with a high compaction density.

[0004] In a first aspect, embodiments of this application provide a positive electrode active material, the positive electrode active material comprising a first active particle and a second active particle, wherein the average particle size of the first active particle is smaller than the average particle size of the second active particle; on the particle size distribution curve of the positive electrode active material, the first active particle has a first peak and the second active particle has a second peak, wherein the ratio r1 of the peak value of the first peak to the peak value of the second peak is in the range of 0.3≤r1≤0.8.

[0005] Furthermore, the ratio r2 of the valley between the first peak and the second peak to the peak value of the first peak is in the range of 0.4≤r2≤0.7.

[0006] Furthermore, the ratio r3 of the valley between the first peak and the second peak to the peak value of the second peak is in the range of 0.2≤r3≤0.4.

[0007] Furthermore, the minimum particle size D'min of the first active particle ranges from 0.1 μm to 0.8 μm; the median particle size D'50 of the first active particle ranges from 0.5 μm to 3 μm; the maximum particle size D'max of the first active particle ranges from 1.2 μm to 5 μm; the minimum particle size D”min of the second active particle ranges from 0.6 μm to 1.3 μm; the median particle size D”50 of the second active particle ranges from 5 μm to 8 μm; and the maximum particle size D”max of the second active particle ranges from 32 μm to 38 μm.

[0008] Furthermore, the particle size distribution of the positive electrode active material satisfies the following: 0.1μm≤Dmin≤1.8μm, 2.2μm≤D10≤6.2μm, 8.3μm≤D50≤21.7μm, 23.1μm≤D90≤29.2μm, and 30.7μm≤Dmax≤36.9μm, where Dmin is the minimum particle size of the positive electrode active material, D10 is the particle size corresponding to a cumulative particle size distribution percentage of 10% for the positive electrode active material, D50 is the particle size corresponding to a cumulative particle size distribution percentage of 50% for the positive electrode active material, D90 is the particle size corresponding to a cumulative particle size distribution percentage of 90% for the positive electrode active material, and Dmax is the maximum particle size of the positive electrode active material.

[0009] Furthermore, in the positive electrode active material, the mass ratio w of the second active particle to the first active particle is in the range of 1.5 ≤ w ≤ 4.

[0010] Furthermore, both the first active particle and the second active particle are sodium iron pyrophosphate; the molar ratio A1 of sodium to phosphorus in the first active particle is in the range of 1.021≤A1≤1.05; the molar ratio B1 of iron to phosphorus in the first active particle is in the range of 0.735≤B1≤0.748.

[0011] Furthermore, the molar ratio A2 of sodium and phosphorus in the second active particle is in the range of 1.002≤A2≤1.018; the molar ratio B2 of iron and phosphorus in the second active particle is in the range of 0.705≤B2≤0.73.

[0012] Furthermore, the molar ratio A of sodium to phosphorus in the positive electrode active material is in the range of 1.008 ≤ A ≤ 1.04; the molar ratio B of iron to phosphorus in the positive electrode active material is in the range of 0.714 ≤ B ≤ 0.748.

[0013] Secondly, embodiments of this application also provide a method for preparing a positive electrode active material, comprising:

[0014] The preparation of the first active particles includes: providing a first sodium source, a first phosphorus source, a first iron source, and a first carbon source; stirring and mixing the first sodium source, the first phosphorus source, the first iron source, and the first carbon source in a solvent to obtain a first slurry, and performing a first spray drying to obtain a first precursor powder; and performing a first sintering on the first precursor powder to obtain the first active particles, wherein the first active particles are sodium iron pyrophosphate.

[0015] The preparation of second active particles includes: providing a second sodium source, a second phosphorus source, a second iron source, and a second carbon source; mixing the second sodium source, the second phosphorus source, the second iron source, and the second carbon source in a solvent to obtain a second slurry, and then performing a second spray drying to obtain a second precursor powder; and performing a second sintering on the second precursor powder to obtain the second active particles, wherein the second active particles are sodium iron pyrophosphate, and the average particle size of the first active particles is smaller than the average particle size of the second active particles; and

[0016] The first active particle and the second active particle are mixed to obtain the positive electrode active material, wherein the first active particle has a first peak and the second active particle has a second peak on the particle size distribution curve of the positive electrode active material, and the ratio r1 of the peak value of the first peak to the peak value of the second peak is in the range of 0.3≤r1≤0.8.

[0017] Furthermore, when preparing the first active particles, the molar ratio A1 of sodium to phosphorus in the first sodium source, the first phosphorus source, and the first iron source is in the range of 1.021≤A1≤1.05, and the molar ratio B1 of iron to phosphorus is in the range of 0.735≤B1≤0.748.

[0018] Furthermore, when preparing the second active particles, the molar ratio A2 of sodium to phosphorus in the second sodium source, the second phosphorus source, and the second iron source is in the range of 1.002≤A2≤1.018; and the molar ratio B2 of iron to phosphorus is in the range of 0.705≤B2≤0.73.

[0019] Furthermore, in the positive electrode active material, the mass ratio w of the second active particle to the first active particle is in the range of 1.5 ≤ w ≤ 4.

[0020] Furthermore, the solid content of the first slurry ranges from 20% to 40%; the temperature during the first spray drying ranges from 95°C to 120°C; and the temperature during the first sintering ranges from 450°C to 620°C.

[0021] The solid content of the second slurry ranges from 20% to 40%; the temperature during the second spray drying ranges from 95°C to 120°C; and the temperature during the second sintering ranges from 450°C to 620°C.

[0022] Thirdly, embodiments of this application also provide a battery, which includes:

[0023] Electrolyte;

[0024] The positive electrode sheet includes the positive active material described in the embodiments of this application;

[0025] A diaphragm is located on one side of the positive electrode plate, and

[0026] The negative electrode is disposed on the side of the diaphragm opposite to the positive electrode.

[0027] The positive electrode active material in this application includes a first active particle and a second active particle. The average particle size of the first active particle is smaller than that of the second active particle. On the particle size distribution curve of the positive electrode active material, the first active particle has a first peak, and the second active particle has a second peak. The ratio r1 of the peak value of the first peak to the peak value of the second peak is in the range of 0.3 ≤ r1 ≤ 0.8. This application, through the compounding of the first and second active particles, allows the smaller first active particles to effectively fill the gaps formed by the accumulation of larger second active particles, without leaving excessive residue. This results in a higher compaction density for the positive electrode active material, leading to a higher energy density when applied to a battery. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a particle size distribution diagram of the positive electrode active material of an embodiment of this application.

[0030] Figure 2 This is a schematic diagram of the preparation method of the positive electrode active material according to an embodiment of this application.

[0031] Figure 3 This is a schematic diagram of the structure of a battery according to an embodiment of this application.

[0032] Figure 4 This is a battery edge according to an embodiment of the present application. Figure 3 A schematic diagram of the cross-sectional structure along the AA direction.

[0033] Figure 5 This is a schematic diagram of the structure of the positive electrode sheet according to an embodiment of this application.

[0034] Figure 6 This is a schematic diagram of the structure of the negative electrode sheet according to an embodiment of this application.

[0035] Explanation of reference numerals in the attached figures:

[0036] 10-First peak, 20-Second peak, 300-Battery, 310-Positive electrode, 311-Positive current collector, 312-Positive active layer, 320-Separator, 330-Negative electrode, 331-Negative current collector, 332-Negative active layer, 340-Shell, 350-End cap assembly. Detailed Implementation

[0037] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0038] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0039] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0040] It should be noted that, for ease of explanation, the same reference numerals denote the same components in the embodiments of this application, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0041] Sodium iron pyrophosphate (Na4Fe3(PO4)2(P2O7), with its three-dimensional sodium ion diffusion channels and sodium superionic conductor structure, exhibits high voltage plateau, high capacity, excellent rate capability, and excellent cycle stability, making it a promising cathode material for large-scale production in sodium-ion batteries. However, the current compaction density of Na4Fe3(PO4)2(P2O7) remains relatively low.

[0042] Please see Figure 1In some embodiments, this application provides a positive electrode active material, which includes a first active particle and a second active particle. The average particle size of the first active particle is smaller than the average particle size of the second active particle. On the particle size distribution curve (i.e., volume fraction-particle size curve) of the positive electrode active material, the first active particle has a first peak 10, and the second active particle has a second peak 20. The ratio r1 of the value a1 of the peak of the first peak 10 and the value a2 of the peak of the second peak 20 is in the range of 0.3≤r1≤0.8.

[0043] The positive electrode active material of this application can be used in batteries, such as sodium-ion batteries, as the positive electrode active material of the positive electrode active layer of the positive electrode sheet of the battery.

[0044] Understandably, such as Figure 1 As shown, r1 = a1 / a2.

[0045] Specifically, the ratio r1 of the value of the first peak 10 to the value of the second peak 20 can be, but is not limited to, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, etc.

[0046] In this embodiment, the ratio r1 of the value of the first peak 10 to the value of the value of the second peak 20 can intuitively reflect the ratio and size range of the first active particles and the second active particles. If r1 is too small, it means that the proportion of the first active particles is too small; if r1 is too large, it means that the proportion of the first active particles is too large. To make the positive electrode active material have a high compaction density, the first active particles (small particles) need to fill the gaps left by the second active particles (large particles). If r1 is too small, it means that there are too few first active particles and too many second active particles. The gaps formed after the second active particles are stacked are also too many, and there are not enough first active particles to fill the gaps left by the second active particles, thereby reducing the compaction density of the positive electrode active material. If r1 is too large, it means that there are too many first active particles and too few second active particles. The gaps formed after the second active particles are stacked are too few, and there are not enough gaps to accommodate the first active particles. The excess first active particles are stacked separately, which also reduces the compaction density of the positive electrode active material. When the ratio r1 of the value of the first peak 10 to the value of the value of the second peak 20 is in the range of 0.3≤r1≤0.8, the first active particles can fill the gaps after the second active particles are stacked perfectly without too much residue. This results in the positive electrode active material having a high compaction density, which, when applied to a battery, gives the battery a high energy density.

[0047] Furthermore, the ratio r1 of the value of the first peak 10 to the value of the second peak 20 is in the range of 0.4≤r1≤0.6. This allows the first active particles to better fill the gaps after the second active particles are stacked, and there will not be too much of the first active particles remaining after filling the gaps. This results in the positive electrode active material having a higher compaction density, which leads to a higher energy density when applied to a battery.

[0048] The positive electrode active material in this application includes a first active particle and a second active particle. The average particle size of the first active particle is smaller than that of the second active particle. On the particle size distribution curve of the positive electrode active material, the first active particle has a first peak 10, and the second active particle has a second peak 20. The ratio r1 of the peak value of the first peak 10 to the peak value of the second peak 20 is in the range of 0.3 ≤ r1 ≤ 0.8. This application, through the compounding of the first and second active particles, allows the smaller first active particles to effectively fill the gaps formed by the accumulation of larger second active particles, without leaving excessive residue. This results in a higher compaction density for the positive electrode active material, leading to a higher energy density when applied to a battery.

[0049] In some embodiments, the ratio r2 of the valley value b1 between the first peak 10 and the second peak 20 to the peak value a1 of the first peak 10 is in the range of 0.4≤r2≤0.7.

[0050] Understandably, such as Figure 1 As shown, r2 = b1 / a1.

[0051] Specifically, r2 can be, but is not limited to, 0.4, 0.43, 0.45, 0.48, 0.5, 0.53, 0.55, 0.58, 0.6, 0.63, 0.65, 0.68, 0.7, etc.

[0052] In this embodiment, the value of r2 represents the size difference between the similar-sized portions of the first active particle (small particle) and the second active particle (large particle) and the size of the first active particle. If r2 is too small, it indicates that the direct interaction between the sizes of the first and second active particles is too low, and the size difference between the first and second active particles is too large and discontinuous. This means that when filling the gaps between the second active particles, smaller first or second active particles are always needed instead of slightly larger ones, resulting in a decrease in the compaction density of the positive electrode active material. If r2 is too large, it indicates that the size difference between the first active particle (small particle) and the second active particle (large particle) is too small, and the small particles cannot fill the gaps between the large particles, which will also reduce the compaction density of the positive electrode active material. By ensuring that 0.4 ≤ r2 ≤ 0.7, the sizes of the first and second active particles can have a suitable overlap. This allows the gaps formed by the accumulation of larger second active particles in the positive electrode active material to be filled first by smaller second active particles, and vice versa. The gaps formed by the accumulation of smaller second active particles can be filled by larger first active particles, and vice versa, until the gaps are filled by the smallest second active particles. This results in a high compaction density for the positive electrode active material, leading to a high energy density in batteries.

[0053] Furthermore, the ratio r2 of the valley value b1 between the first peak 10 and the second peak 20 to the peak value a1 of the first peak 10 is in the range of 0.45 ≤ r2 ≤ 0.6. This allows the positive electrode active material to have a higher compaction density, resulting in a higher energy density when applied to a battery.

[0054] In some embodiments, the ratio r3 of the valley value b1 between the first peak 10 and the second peak 20 to the peak value a2 of the second peak 20 is in the range of 0.2≤r3≤0.4.

[0055] Understandably, such as Figure 1 As shown, r3 = b1 / a2.

[0056] Specifically, r3 can be, but is not limited to, 0.2, 0.22, 0.24, 0.25, 0.26, 0.28, 0.3, 0.32, 0.34, 0.35, 0.36, 0.38, 0.4, etc.

[0057] In this embodiment, the value of r3 represents the size difference between the similar-sized portions of the first active particle (small particle) and the second active particle (large particle) and the size of the second active particle. If r3 is too small, it indicates that the direct interaction between the sizes of the first and second active particles is too low, and the size difference between the first and second active particles is too large and discontinuous. This means that when filling the gaps between the second active particles, smaller first or second active particles are always needed instead of slightly larger ones, resulting in a decrease in the compaction density of the positive electrode active material. If r3 is too large, it indicates that the size difference between the first active particle (small particle) and the second active particle (large particle) is too small, and the small particles cannot fill the gaps between the large particles, which will also reduce the compaction density of the positive electrode active material. By ensuring that 0.2 ≤ r3 ≤ 0.4, the sizes of the first and second active particles can have a suitable overlap. This allows the gaps formed by the accumulation of larger second active particles in the positive electrode active material to be filled first by smaller second active particles, and vice versa. The gaps formed by the accumulation of smaller second active particles can be filled by larger first active particles, and vice versa, until the gaps are filled by the smallest second active particles. This results in a high compaction density for the positive electrode active material, leading to a high energy density in batteries.

[0058] In some embodiments, the minimum particle size D'min of the first active particle ranges from 0.1 μm to 0.8 μm; the median particle size D'50 of the first active particle ranges from 0.5 μm to 3 μm; the maximum particle size D'max of the first active particle ranges from 1.2 μm to 5 μm; the minimum particle size D”min of the second active particle ranges from 0.6 μm to 1.3 μm; the median particle size D”50 of the second active particle ranges from 5 μm to 8 μm; and the maximum particle size D”max of the second active particle ranges from 32 μm to 38 μm.

[0059] Specifically, the minimum particle size D'min of the first active particle can be, but is not limited to, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, etc. If the minimum particle size D'min of the first active particle is too small or too large, the particle sizes of the first and second active particles will not form an optimal blend, thus reducing the compaction density of the positive electrode active material.

[0060] Specifically, the median particle size D'50 of the first active particle can be, but is not limited to, 0.5 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, or 3 μm. If the median particle size D'50 of the first active particle is too small or too large, the particle sizes of the first and second active particles will not form an optimal blend, thus reducing the compaction density of the positive electrode active material.

[0061] Specifically, the maximum particle size D'max of the first active particle can be, but is not limited to, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, 3.0 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4.0 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, 5 μm, etc. If the maximum particle size D'max of the first active particle is too small or too large, the particle sizes of the first active particle and the second active particle will not form an optimal composite, both of which will reduce the compaction density of the positive electrode active material.

[0062] Specifically, the minimum particle size D”min of the second active particle can be, but is not limited to, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, etc. If the minimum particle size D”min of the second active particle is too small or too large, the particle sizes of the first active particle and the second active particle will not form an optimal mixture, which will reduce the compaction density of the positive electrode active material.

[0063] Specifically, the median particle size D”50 of the second active particle can be, but is not limited to, 5.0 μm, 5.2 μm, 5.4 μm, 5.6 μm, 5.8 μm, 6.0 μm, 6.2 μm, 6.4 μm, 6.6 μm, 6.8 μm, 7.0 μm, 7.2 μm, 7.4 μm, 7.6 μm, 7.8 μm, 8 μm, etc. If the median particle size D”50 of the second active particle is too small or too large, the particle sizes of the first active particle and the second active particle will not form an optimal mixture, and both will reduce the compaction density of the positive electrode active material.

[0064] Specifically, the maximum particle size D”max of the second active particle can be, but is not limited to, 32μm, 33μm, 34μm, 35μm, 36μm, 37μm, 38μm, etc. If the maximum particle size D”max of the second active particle is too small or too large, the particle sizes of the first active particle and the second active particle will not form an optimal combination, which will reduce the compaction density of the positive electrode active material.

[0065] In this embodiment, by designing the particle size distribution of the first active particle and the second active particle, the gaps formed by the accumulation of larger particles can be filled by smaller particles, and the gaps formed by smaller particles can be filled by even smaller particles. This results in an optimal size combination between the first active particle and the second active particle, so that the obtained positive electrode active material has a high compaction density, and the battery made using this positive electrode active material has a high energy density.

[0066] In some embodiments, the particle size distribution of the positive electrode active material satisfies the following: 0.1μm≤Dmin≤1.8μm, 2.2μm≤D10≤6.2μm, 8.3μm≤D50≤21.7μm, 23.1μm≤D90≤29.2μm, 30.7μm≤Dmax≤36.9μm, where Dmin is the minimum particle size of the positive electrode active material, D10 is the particle size corresponding to a cumulative particle size distribution percentage of 10% for the positive electrode active material, D50 is the particle size corresponding to a cumulative particle size distribution percentage of 50% for the positive electrode active material, D90 is the particle size corresponding to a cumulative particle size distribution percentage of 90% for the positive electrode active material, and Dmax is the maximum particle size of the positive electrode active material.

[0067] Specifically, the minimum particle size Dmin of the positive electrode active material can be, but is not limited to, 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, etc. If the minimum particle size Dmin of the positive electrode active material is too small or too large, the sizes of the particles of different sizes will not form an optimal blend, thus reducing the compaction density of the positive electrode active material.

[0068] Specifically, the D10 of the positive electrode active material can be, but is not limited to, 2.2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6.0 μm, 6.2 μm, etc. If the D10 of the positive electrode active material is too small or too large, the particle sizes of different dimensions will not form an optimal blend, thus reducing the compaction density of the positive electrode active material.

[0069] Specifically, the D50 of the positive electrode active material can be, but is not limited to, 8.3 μm, 9 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, 21.7 μm, etc. If the D50 of the positive electrode active material is too small or too large, the particle sizes of different diameters will not form an optimal blend, thus reducing the compaction density of the positive electrode active material.

[0070] Specifically, the D90 of the positive electrode active material can be, but is not limited to, 23.1 μm, 23.5 μm, 24 μm, 24.5 μm, 25 μm, 25.5 μm, 26 μm, 26.5 μm, 27 μm, 27.5 μm, 28 μm, 28.5 μm, 29.0 μm, and 29.2 μm. If the D90 of the positive electrode active material is too small or too large, the particle sizes of different dimensions will not form an optimal blend, thus reducing the compaction density of the positive electrode active material.

[0071] Specifically, the Dmax of the positive electrode active material can be, but is not limited to, 30.7 μm, 31 μm, 31.5 μm, 32 μm, 32.5 μm, 33 μm, 33.5 μm, 34 μm, 34.5 μm, 35 μm, 35.5 μm, 36 μm, 36.5 μm, and 36.9 μm. If the Dmax of the positive electrode active material is too small or too large, the particle sizes of different dimensions will not form an optimal blend, thus reducing the compaction density of the positive electrode active material.

[0072] In this embodiment, by designing the particle size distribution of the positive electrode active material, Dmin, D10, D50, D90 and Dmax, the gaps formed by the accumulation of larger particles can be filled by smaller particles, and the gaps formed by smaller particles can be filled by even smaller particles. This results in the positive electrode active material having a high compaction density, which, when applied to a battery, results in a battery with a high energy density.

[0073] In some embodiments, the mass ratio w of the second active particle to the first active particle in the positive electrode active material is in the range of 1.5 ≤ w ≤ 4.

[0074] Specifically, in the positive electrode active material, the mass ratio w of the second active particle to the first active particle can be, but is not limited to, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4, etc.

[0075] In this embodiment, if the mass ratio w of the second active particle to the first active particle is too small, it indicates that the proportion of the second active particle is too low and the proportion of the first active particle is too high. This means that the gaps left after the second active particle stacking are insufficient to fill all the first active particles, and the excess first active particles are stacked separately, reducing the compaction density of the positive electrode active material. Conversely, if the mass ratio w of the second active particle to the first active particle is too high, it indicates that the proportion of the second active particle is too high and the proportion of the first active particle is too low. This results in more gaps left after the second active particle stacking, and insufficient second active particles to fill these gaps, still reducing the compaction density of the positive electrode active material. When the mass ratio w of the second active particle to the first active particle is in the range of 1.5 ≤ w ≤ 4, the ratio of the first active particle to the second active particle is more appropriate. The first active particles can just fill the gaps left after the second active particle stacking, resulting in a higher compaction density for the positive electrode active material. Consequently, when the positive electrode active material is used in a battery, the battery has a higher energy density.

[0076] In some embodiments, both the first active particle and the second active particle are sodium iron pyrophosphate (molecular formula Na4Fe3(PO4)2(P2O7)). Sodium iron pyrophosphate has excellent characteristics such as a high voltage plateau, high capacity, good rate performance, and high cycle stability.

[0077] It should be noted that the molecular formula Na4Fe3(PO4)2(P2O7) of sodium iron pyrophosphate in this application is merely a theoretical molecular formula obtained based on the valence states of each element. The ratio of sodium to phosphorus and the ratio of iron to phosphorus in the first and second active particles of this application should not be interpreted as the quantitative ratio in the molecular formula. The ratio of sodium to phosphorus and the ratio of iron to phosphorus in the first and second active particles of this application shall be based on the specific description in the corresponding embodiments of this application. The molecular formula should not be interpreted as a limitation on the specific elemental composition of the first and second active particles of this application.

[0078] Optionally, the molar ratio A1 of sodium (Na) and phosphorus (P) in the first active particle is in the range of 1.021 ≤ A1 ≤ 1.05.

[0079] Specifically, the molar ratio A1 of sodium and phosphorus in the first active particle can be, but is not limited to, 1.021, 1.023, 1.025, 1.028, 1.030, 1.032, 1.035, 1.038, 1.040, 1.042, 1.045, 1.048, 1.05, etc.

[0080] In this embodiment, when preparing the first active particles, if the molar ratio A1 of sodium and phosphorus in the raw materials used to prepare the first active particles is too small, the size of the first active particles will be too large, making it impossible to blend well with the larger second active particles, thus reducing the compaction density of the positive electrode active material. Increasing the molar ratio A1 of sodium and phosphorus in the raw materials used to prepare the first active particles can reduce the size of the first active particles. However, if the molar ratio A1 of sodium and phosphorus in the raw materials used to prepare the first active particles is too large, the proportion of sodium in the first active particles will be too high. When the positive electrode active material is applied to the battery, the excess sodium cannot contribute to the battery's capacity, thus reducing the volumetric energy density and gravimetric energy density of the first active particles, further reducing the specific capacity of the battery. In addition, if the molar ratio A1 of sodium and phosphorus is too large, the size of the first active particles will be too small or there will be too many small particles, which will also prevent them from blending well with the larger second active particles, reducing the compaction density of the positive electrode active material.

[0081] Optionally, the molar ratio B1 of iron (Fe) and phosphorus (P) in the first active particle is in the range of 0.735 ≤ B1 ≤ 0.748.

[0082] Specifically, the molar ratio B1 of iron and phosphorus in the first active particle can be, but is not limited to, 0.735, 0.736, 0.738, 0.740, 0.742, 0.744, 0.746, 0.748, etc.

[0083] In this embodiment, when preparing the first active particles, if the molar ratio B1 of iron (Fe) and phosphorus (P) in the raw materials used to prepare the first active particles is too small, the resulting first active particles will be too large, making it difficult to blend well with the larger second active particles and reducing the compaction density of the cathode active material. Increasing the molar ratio B1 of iron and phosphorus in the raw materials used to prepare the first active particles can reduce the size of the resulting first active particles. However, if the molar ratio B1 of iron and phosphorus in the raw materials used to prepare the first active particles is too large, the resulting first active particles will be too small or there will be too many small particles, which will also prevent them from blending well with the larger second active particles and reduce the compaction density of the cathode active material.

[0084] Optionally, the molar ratio A2 of sodium and phosphorus in the second active particle is in the range of 1.002≤A2≤1.018.

[0085] Specifically, the molar ratio A2 of sodium and phosphorus in the second active particle can be, but is not limited to, 1.002, 1.003, 1.005, 1.008, 1.01, 1.012, 1.014, 1.016, 1.018, etc.

[0086] In this embodiment, when preparing the second active particles, if the molar ratio A2 of sodium and phosphorus in the raw materials used to prepare the second active particles is too small, the sodium source will be insufficient, reducing the volumetric energy density and gravimetric energy density of the prepared second active particles. When the positive electrode active material is applied to a battery, this reduces the specific capacity of the battery. If the molar ratio A2 of sodium and phosphorus in the raw materials used to prepare the second active particles is too large, the size of the prepared second active particles will be too small, making it impossible to form a good composite with the small-diameter first active particles, thus reducing the compaction density of the positive electrode active material.

[0087] Optionally, the molar ratio B2 of iron and phosphorus in the second active particle is in the range of 0.705 ≤ B2 ≤ 0.73.

[0088] Specifically, the molar ratio B2 of iron and phosphorus in the second active particle can be, but is not limited to, 0.705, 0.706, 0.708, 0.710, 0.712, 0.714, 0.716, 0.718, 0.720, 0.722, 0.724, 0.726, 0.728, 0.73, etc.

[0089] In this embodiment, during the preparation of the second active particles, if the molar ratio B1 of iron (Fe) to phosphorus (P) in the raw materials used to prepare the second active particles is too small, the iron source in the resulting second active particles will be insufficient, thereby reducing the volumetric energy density and gravimetric energy density of the second active particles. When applied to a battery, this reduces the specific capacity of the battery. Conversely, if the molar ratio B1 of iron to phosphorus in the raw materials used to prepare the second active particles is too large, the amount of inactive iron in the resulting second active particles will increase, similarly reducing the volumetric energy density and gravimetric energy density of the second active particles. When applied to a battery, this also reduces the specific capacity of the battery.

[0090] The sodium-to-phosphorus ratio A1 and iron-to-phosphorus ratio B1 of the first active particle in this application embodiment, and the sodium-to-phosphorus ratio A2 and iron-to-phosphorus ratio B2 of the second active particle, can all be measured using inductively coupled plasma optical emission spectrometry (ICP-OES). During the preparation of the first and second active particles, A1, B1, A2, and B2 can be controlled by the proportions of the raw materials.

[0091] In some embodiments, the molar ratio A of sodium to phosphorus in the positive electrode active material is in the range of 1.008 ≤ A ≤ 1.04.

[0092] Specifically, the molar ratio A of sodium to phosphorus in the positive electrode active material can be, but is not limited to, 1.008, 1.01, 1.012, 1.014, 1.016, 1.018, 1.02, 1.022, 1.024, 1.026, 1.028, 1.03, 1.032, 1.034, 1.036, 1.038, 1.04, etc.

[0093] In this embodiment, when preparing the positive electrode active material, if the molar ratio A of sodium and phosphorus in the raw materials used to prepare the positive electrode active material is too small, the combination of large and small particles in the positive electrode active material will not be optimal, reducing the compaction density of the positive electrode active material. Furthermore, it will result in insufficient sodium source, reducing the volumetric energy density and gravimetric energy density of the obtained second active particles. When the positive electrode active material is applied to a battery, this reduces the specific capacity of the battery. Conversely, if the molar ratio A of sodium and phosphorus in the raw materials used to prepare the positive electrode active material is too large, the proportion of sodium in the obtained positive electrode active material will be excessive. When the positive electrode active material is applied to a battery, the excess sodium cannot contribute to the battery's capacity, thus reducing the volumetric energy density and gravimetric energy density of the positive electrode active material, further reducing the specific capacity of the battery. Additionally, if the molar ratio A1 of sodium and phosphorus is too large, the combination of large and small particles in the positive electrode active material will not be optimal, reducing the compaction density of the positive electrode active material.

[0094] Optionally, the molar ratio B of iron to phosphorus in the positive electrode active material is in the range of 0.714 ≤ B ≤ 0.748.

[0095] Specifically, the molar ratio B of iron to phosphorus in the positive electrode active material can be, but is not limited to, 0.714, 0.716, 0.718, 0.720, 0.722, 0.724, 0.726, 0.728, 0.73, 0.732, 0.734, 0.736, 0.738, 0.74, 0.742, 0.744, 0.746, 0.748, etc.

[0096] In this embodiment, when preparing the positive electrode active material, if the molar ratio B of iron (Fe) and phosphorus (P) in the raw materials used to prepare the positive electrode active material is too small, the combination of large and small particles in the positive electrode active material will not reach the optimal level, reducing the compaction density of the positive electrode active material. Furthermore, it will result in insufficient iron source in the positive electrode active material, thereby reducing the volumetric energy density and gravimetric energy density of the second active particles, and consequently reducing the specific capacity of the battery when applied to a battery. Conversely, if the molar ratio B1 of iron and phosphorus in the raw materials used to prepare the positive electrode active material is too large, the amount of inactive iron in the resulting positive electrode active material will increase, similarly reducing the volumetric energy density and gravimetric energy density of the positive electrode active material, and consequently reducing the specific capacity of the battery when applied to a battery. Furthermore, it will also result in the combination of large and small particles in the positive electrode active material not reaching the optimal level, reducing the compaction density of the positive electrode active material.

[0097] The powder compaction density of the positive electrode active material in this application embodiment ranges from 2.05 g / cm³. 3 Up to 2.35 g / cm 3 Specifically, it can be, but is not limited to, 2.05 g / cm³. 3 2.10 g / cm 3 2.15g / cm 3 2.20g / cm 3 2.25g / cm 3 2.30g / cm 3 2.35g / cm 3 wait.

[0098] In the embodiments of this application, when the numerical range a to b is involved, unless otherwise specified, the numerical value can be any value between a and b, including the endpoint value a and the endpoint value b.

[0099] The powder compaction density test method of this application is as follows: 2g to 3g of Na4Fe3(PO4)2(P2O7) powder is added into a mold with a diameter of 13mm, pressurized to 3 tons, held for 10s and then released. The mass and volume of the compressed cylinder are measured and the powder compaction density is calculated.

[0100] The compaction density of the electrode layers (the obtained positive electrode sheets) of the positive electrode active material in this application embodiment ranges from 2.4 g / cm³. 3 Up to 2.4 g / cm 3 Specifically, it can be, but is not limited to, 2.10 g / cm³. 3 2.15g / cm 3 2.20g / cm 3 2.25g / cm 3 2.30g / cm3 2.35g / cm 3 2.4g / cm 3 wait.

[0101] The method for testing the compaction density of the electrode layer in this application is as follows: the thickness of the aluminum foil and the mass of the aluminum foil cut into 12mm round pieces are measured in advance. Then, the thickness of the positive electrode sheet made of the positive electrode active material is measured, and the positive electrode sheet is cut into 12mm round pieces and weighed. The mass and volume of the positive electrode active material on the positive electrode sheet are calculated, and then the compaction density of the positive electrode active material on the positive electrode sheet is calculated.

[0102] The positive electrode active material of this application embodiment has a high powder compaction density and electrode layer compaction density.

[0103] The positive electrode active material of this application embodiment can be prepared by the method described in the following embodiments of this application. In addition, it can also be prepared by other methods. The preparation method of this application embodiment is only one or more preparation methods of the positive electrode active material of this application and should not be construed as a limitation on the positive electrode active material provided in the embodiments of this application.

[0104] Please see Figure 2 This application provides a method for preparing a positive electrode active material, comprising:

[0105] S201, preparing the first active particles, comprising: providing a first sodium source, a first phosphorus source, a first iron source and a first carbon source; stirring and mixing the first sodium source, the first phosphorus source, the first iron source and the first carbon source in a solvent to obtain a first slurry, and performing a first spray drying to obtain a first precursor powder; and performing a first sintering on the first precursor powder to obtain the first active particles, wherein the first active particles are sodium iron pyrophosphate.

[0106] S202, preparing the second active particles, includes: providing a second sodium source, a second phosphorus source, a second iron source, and a second carbon source; mixing the second sodium source, the second phosphorus source, the second iron source, and the second carbon source in a solvent to obtain a second slurry, and performing a second spray drying to obtain a second precursor powder; and performing a second sintering on the second precursor powder to obtain the second active particles, wherein the second active particles are sodium iron pyrophosphate, and the average particle size of the first active particles is smaller than the average particle size of the second active particles; and

[0107] S203, the first active particles and the second active particles are mixed to obtain the positive electrode active material, wherein the first active particles have a first peak 10 and the second active particles have a second peak 20 on the particle size distribution curve of the positive electrode active material, and the ratio r1 of the peak value of the first peak 10 to the peak value of the second peak 20 is in the range of 0.3≤r1≤0.8.

[0108] For a detailed description of the first active particle, the second active particle, and the positive electrode active material, please refer to the description in the corresponding section of the above embodiments, which will not be repeated here.

[0109] The positive electrode active material prepared by the method of this application embodiment includes a first active particle and a second active particle. The average particle size of the first active particle is smaller than that of the second active particle. On the particle size distribution curve of the positive electrode active material, the first active particle has a first peak 10, and the second active particle has a second peak 20. The ratio r1 of the peak value of the first peak 10 to the peak value of the second peak 20 is in the range of 0.3 ≤ r1 ≤ 0.8. By combining the first active particle and the second active particle, this application enables the smaller first active particle to fill the gaps formed by the accumulation of the larger second active particle, and there will not be too much first active particle left after filling the gaps. This results in a higher compaction density of the positive electrode active material, which leads to a higher energy density when applied to a battery.

[0110] Optionally, the first sodium source may include sodium dihydrogen phosphate, sodium pyrophosphate, sodium carbonate, sodium acetate, and amorphous sodium with non-fixed components. x Fe y P z O k At least one of the compounds, and of these compounds containing water of crystallization.

[0111] Optionally, the first phosphorus source may include sodium dihydrogen phosphate, sodium pyrophosphate, ammonium dihydrogen phosphate, etc., as well as amorphous Na with non-fixed composition. x Fe y P z O k At least one of the compounds, and of these compounds containing water of crystallization.

[0112] Optionally, the first iron source may include ferrous oxalate, ferric nitrate, ferrous sulfate, and amorphous Na with non-fixed composition. x Fe y P z O k At least one of the following compounds, and compounds containing water of crystallization. For example, ferrous oxalate can be replaced with ferrous oxalate dihydrate.

[0113] Optionally, the first carbon source is at least one selected from glucose, sucrose, starch, polyethylene glycol, ascorbic acid, citric acid, carbon nanotubes, graphene, etc. The first active particles prepared in this application have poor conductivity. Adding a first carbon source during the preparation of the first active particles can improve their conductivity.

[0114] Optionally, when preparing the first active particles, the molar ratio A1 of sodium to phosphorus in the first sodium source, the first phosphorus source, and the first iron source is in the range of 1.021≤A1≤1.05, and the molar ratio B1 of iron to phosphorus is in the range of 0.735≤B1≤0.748.

[0115] Specifically, in the first sodium source, the first phosphorus source, and the first iron source, the molar ratio A1 of sodium to phosphorus can be, but is not limited to, 1.021, 1.023, 1.025, 1.028, 1.030, 1.032, 1.035, 1.038, 1.040, 1.042, 1.045, 1.048, 1.05, etc. If the molar ratio A1 of sodium to phosphorus in the first sodium source and the first phosphorus source is too small, the size of the resulting first active particles will be too large, making it difficult to properly combine with the larger second active particles, thus reducing the compaction density of the positive electrode active material. Increasing the molar ratio A1 of sodium to phosphorus in the first sodium source and the first phosphorus source can reduce the size of the resulting first active particles. However, when the molar ratio A1 of sodium and phosphorus in the first sodium source and the first phosphorus source is too large, the proportion of sodium in the prepared first active particles is too high. When the positive electrode active material is applied to the battery, the excess sodium cannot play a role in the battery capacity, thereby reducing the volumetric energy density and gravimetric energy density of the first active particles, and further reducing the specific capacity of the battery. In addition, if the molar ratio A1 of sodium and phosphorus in the first sodium source and the first phosphorus source is too large, the size of the prepared first active particles will be too small or there will be too many small particles. Similarly, they cannot be well compounded with the larger second active particles, reducing the compaction density of the positive electrode active material.

[0116] Specifically, the molar ratio B1 of iron and phosphorus in the first phosphorus source and the first iron source can be, but is not limited to, 0.735, 0.736, 0.738, 0.740, 0.742, 0.744, 0.746, 0.748, etc. If the molar ratio B1 of iron and phosphorus in the first phosphorus source and the first iron source is too small, the resulting first active particles will be too large, making it difficult to blend well with the larger second active particles, thus reducing the compaction density of the cathode active material. Increasing the molar ratio B1 of iron and phosphorus in the raw materials can reduce the size of the resulting first active particles. However, if the molar ratio B1 of iron and phosphorus in the first phosphorus source and the first iron source is too large, the resulting first active particles will be too small or there will be too many small particles, similarly preventing good blending with the larger second active particles and reducing the compaction density of the cathode active material.

[0117] Optionally, in S201, the preparation of the first active particles includes: stirring the first sodium source, the first phosphorus source, the first iron source, and the first carbon source in water (understandably, the solvent can be water) and performing a first sand milling treatment to obtain a first slurry; placing the first slurry in a spray dryer for a first spray drying to obtain a first precursor powder; and performing a first sintering of the first precursor powder in a sintering furnace under an inert atmosphere (such as nitrogen, helium, argon, etc.) to obtain the first active particles, wherein the first active particles are sodium iron pyrophosphate.

[0118] In this embodiment, before the first spray drying, the raw materials (i.e., the first sodium source, the first phosphorus source, the first iron source, and the first carbon source) are first mixed by sand milling. The first sand milling can reduce the particle size of the raw materials, providing a prerequisite for the formation of sodium iron pyrophosphate. In addition, the first sand milling can fully mix the soluble and insoluble substances in the raw materials, avoiding uneven mixing of the raw materials when there are multiple insoluble raw materials, which would increase the probability of impurity phases in the final sodium iron pyrophosphate (first active particles).

[0119] Optionally, the solid content of the first slurry ranges from 20% to 40%. Specifically, the solid content of the first slurry can be, but is not limited to, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, etc. If the solid content of the first slurry is too low, the yield of the first active particles will be low, and too much solvent will cause the solvent to evaporate during the spray drying process, easily creating pores in the obtained first active particles and reducing the energy density of the obtained first active particles. If the solid content of the first slurry is too high, it will increase the difficulty of the first sand milling, or even prevent the first sand milling from being carried out sufficiently.

[0120] Optionally, the first milling process can be from 0.5 h to 4 h. Specifically, the first milling process can be, but is not limited to, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, etc. If the first milling time is too short, the size of the raw material will be too large, and the size of the final first active particles Na4Fe3(PO4)2(P2O7) will also be too large; if the first milling time is too long, it will not reduce the particle size of the raw material, but it will reduce the production efficiency of the first active particles.

[0121] Optionally, the rotation speed of the first sand mill can be from 1000 rpm to 4000 rpm. Specifically, the rotation speed of the first sand mill can be, but is not limited to, 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, 3500 rpm, 4000 rpm, etc. If the rotation speed of the first sand mill is too slow, the grinding effect on the insoluble raw materials in the first sodium source, first phosphorus source, first iron source, and first carbon source will be too poor, the size of the raw materials will be too large, and the synthesized sodium iron pyrophosphate will easily contain impurities; if the rotation speed of the first sand mill is too high, it will easily put a burden on the first sand mill.

[0122] Optionally, the temperature range for the first spray drying is 95°C to 120°C. Specifically, the temperature for the first spray drying can be, but is not limited to, 95°C, 98°C, 100°C, 103°C, 105°C, 108°C, 110°C, 113°C, 115°C, 118°C, and 120°C. If the temperature during the first spray drying is too low, the raw material will contain too much moisture, which will damage the particle morphology of the raw material. In addition, the moisture contains soluble raw materials, which are not uniformly combined with the insoluble raw materials during spray drying. The soluble raw materials will then be enriched again on the insoluble raw materials during sintering, resulting in the formation of impurity phases in the synthesized sodium ferric pyrophosphate. If the temperature during the first spray drying is too high, the solvent (water) will evaporate too quickly, easily leaving pores inside the first active particles, thereby reducing the compaction density. In addition, it wastes energy and increases the production cost of the first active particles.

[0123] Optionally, the first sintering temperature ranges from 450°C to 620°C; specifically, the first sintering temperature can be, but is not limited to, 450°C, 480°C, 500°C, 520°C, 540°C, 560°C, 580°C, 600°C, etc. If the first sintering temperature is too low, the crystallinity of the resulting first active particles will be too low, resulting in poor electrical performance; in addition, if the first sintering temperature is too low, the carbonization degree of the first carbon source will be reduced, thus reducing the conductivity of the first active particles; if the first sintering temperature is too high, Na4Fe3(PO4)2(P2O7) (the first active particles) will undergo phase separation, easily generating low-activity impurity phases, reducing the energy density of the first active particles, and consequently reducing the energy density of the battery when applied to a battery.

[0124] Furthermore, the temperature range of the first sintering is 500°C to 550°C. When the temperature of the first sintering is within this range, the resulting Na4Fe3(PO4)2(P2O7) particles can have higher conductivity and produce fewer low-activity impurity phases, resulting in higher energy density.

[0125] Optionally, the first sintering time can range from 2 hours to 48 hours. Specifically, the first sintering time can be, but is not limited to, 2 hours, 4 hours, 8 hours, 12 hours, 16 hours, 20 hours, 24 hours, 28 hours, 32 hours, 36 hours, 40 hours, 44 hours, 48 ​​hours, etc. If the first sintering time is too short, the crystallinity of the resulting first active particles will be too low, resulting in poor electrical performance; in addition, the carbonization degree of the first carbon source will decrease, reducing the conductivity of the first active particles. If the first sintering time is too long, Na4Fe3(PO4)2(P2O7) (the first active particles) will undergo phase separation, easily generating low-activity impurity phases, reducing the energy density of the first active particles, and consequently reducing the energy density of the battery when applied to a battery.

[0126] Optionally, the second sodium source may include sodium dihydrogen phosphate, sodium pyrophosphate, sodium carbonate, sodium acetate, and amorphous sodium with non-fixed components. x Fe y P z O k At least one of the compounds, and of these compounds containing water of crystallization.

[0127] Optionally, the second phosphorus source may include sodium dihydrogen phosphate, sodium pyrophosphate, ammonium dihydrogen phosphate, etc., as well as amorphous Na with non-fixed composition. x Fe y P z O k At least one of the compounds, and of these compounds containing water of crystallization.

[0128] Optionally, the second iron source may include ferrous oxalate, ferric nitrate, ferrous sulfate, and amorphous Na with non-fixed composition. x Fe y P z O k At least one of the following compounds, and compounds containing water of crystallization. For example, ferrous oxalate can be replaced with ferrous oxalate dihydrate.

[0129] Optionally, the second carbon source is at least one selected from glucose, sucrose, starch, polyethylene glycol, ascorbic acid, citric acid, carbon nanotubes, graphene, etc. The second active particles prepared in this application have poor conductivity. Adding a second carbon source during the preparation of the second active particles can improve their conductivity.

[0130] Optionally, when preparing the second active particles, the molar ratio A2 of sodium to phosphorus in the second sodium source, the second phosphorus source and the second iron source is in the range of 1.002≤A2≤1.018; and the molar ratio B2 of iron to phosphorus is in the range of 0.705≤B2≤0.73.

[0131] Specifically, in the second sodium source, the second phosphorus source, and the second iron source, the molar ratio A2 of sodium to phosphorus can be, but is not limited to, 1.002, 1.003, 1.005, 1.008, 1.01, 1.012, 1.014, 1.016, 1.018, etc. If the molar ratio A2 of sodium to phosphorus in the second sodium source, the second phosphorus source, and the second iron source is too small, the sodium source will be insufficient, reducing the volumetric energy density and gravimetric energy density of the obtained second active particles. When the positive electrode active material is used in a battery, this reduces the specific capacity of the battery. If the molar ratio A2 of sodium to phosphorus in the second sodium source, the second phosphorus source, and the second iron source is too large, the size of the obtained second active particles will be too small, making it impossible to form a good composite with the small-diameter first active particles, thus reducing the compaction density of the positive electrode active material.

[0132] Specifically, in the second sodium source, the second phosphorus source, and the second iron source, the molar ratio B2 of iron to phosphorus can be, but is not limited to, 0.705, 0.706, 0.708, 0.710, 0.712, 0.714, 0.716, 0.718, 0.720, 0.722, 0.724, 0.726, 0.728, 0.73, etc. If the molar ratio B2 of iron to phosphorus in the second sodium source, the second phosphorus source, and the second iron source is too small, the iron source in the resulting second active particles will be insufficient, thereby reducing the volumetric energy density and gravimetric energy density of the second active particles, and thus reducing the specific capacity of the battery when applied. If the molar ratio B2 of iron to phosphorus in the second sodium source, the second phosphorus source, and the second iron source is too large, the inactive iron in the resulting second active particles will increase, similarly reducing the volumetric energy density and gravimetric energy density of the second active particles, and thus reducing the specific capacity of the battery when applied.

[0133] Optionally, in S202, the preparation of the second active particles includes: stirring the second sodium source, the second phosphorus source, the second iron source, and the second carbon source in water (understandably, the solvent can be water) and performing a second sand milling treatment to obtain a second slurry; placing the second slurry in a spray dryer for a second spray drying to obtain a second precursor powder; and performing a second sintering of the second precursor powder in a sintering furnace under an inert atmosphere (such as nitrogen, helium, argon, etc.) to obtain the second active particles, wherein the second active particles are sodium iron pyrophosphate.

[0134] In this embodiment, before the second spray drying, the raw materials (i.e., the second sodium source, the second phosphorus source, the second iron source, and the second carbon source) are first subjected to a second sand milling process for mixing. The second sand milling can reduce the particle size of the raw materials, providing a prerequisite for the formation of sodium iron pyrophosphate. In addition, the second sand milling can fully and uniformly mix the soluble and insoluble substances in the raw materials, avoiding uneven mixing of the raw materials when there are multiple insoluble raw materials, which would increase the probability of generating impurities in the final sodium iron pyrophosphate (second active particles).

[0135] Optionally, the solid content of the second slurry ranges from 20% to 40%. Specifically, the solid content of the second slurry can be, but is not limited to, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, etc. If the solid content of the second slurry is too low, the yield of the second active particles will be low, and too much solvent will cause the solvent to evaporate during the spray drying process, easily creating pores in the obtained second active particles and reducing the energy density of the obtained second active particles. If the solid content of the second slurry is too high, it will increase the difficulty of the second sand milling, or even prevent the second sand milling from being carried out sufficiently.

[0136] Optionally, the second milling process can be from 0.5 h to 4 h. Specifically, the second milling process can be, but is not limited to, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, etc. If the second milling time is too short, the size of the raw material will be too large, and the size of the final obtained second active particles Na4Fe3(PO4)2(P2O7) will also be too large; if the second milling time is too long, it will not reduce the particle size of the raw material, but it will reduce the production efficiency of the second active particles.

[0137] Optionally, the rotation speed of the second sand mill can be from 1000 rpm to 4000 rpm. Specifically, the rotation speed of the second sand mill can be, but is not limited to, 1000 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm, 3500 rpm, 4000 rpm, etc. If the rotation speed of the second sand mill is too slow, the grinding effect on the insoluble raw materials in the second sodium source, second phosphorus source, second iron source, and second carbon source will be too poor, the size of the raw materials will be too large, and the synthesized sodium iron pyrophosphate will easily contain impurities; if the rotation speed of the second sand mill is too high, it will easily put a burden on the second sand mill.

[0138] Optionally, the temperature range for the second spray drying is 95°C to 120°C. Specifically, the temperature for the second spray drying can be, but is not limited to, 95°C, 98°C, 100°C, 103°C, 105°C, 108°C, 110°C, 113°C, 115°C, 118°C, and 120°C. If the temperature during the second spray drying is too low, the raw material will contain too much moisture, which will damage the particle morphology of the raw material. In addition, the moisture contains soluble raw materials, which are not uniformly combined with the insoluble raw materials during spray drying. The soluble raw materials will then be enriched again on the insoluble raw materials during sintering, resulting in the formation of impurity phases in the synthesized sodium ferric pyrophosphate. If the temperature during the second spray drying is too high, the solvent (water) will evaporate too quickly, easily leaving pores inside the second active particles, thereby reducing the compaction density. In addition, it wastes energy and increases the production cost of the first active particles.

[0139] Optionally, the second sintering temperature ranges from 450°C to 620°C; specifically, the second sintering temperature can be, but is not limited to, 450°C, 480°C, 500°C, 520°C, 540°C, 560°C, 580°C, 600°C, etc. If the second sintering temperature is too low, the crystallinity of the resulting second active particles will be too low, resulting in poor electrical performance; in addition, if the second sintering temperature is too low, the carbonization degree of the second carbon source will be reduced, thus reducing the conductivity of the second active particles; if the second sintering temperature is too high, Na4Fe3(PO4)2(P2O7) (the second active particles) will undergo phase separation, easily generating low-activity impurity phases, reducing the energy density of the second active particles, and consequently reducing the energy density of the battery when applied to a battery.

[0140] Furthermore, the second sintering temperature ranges from 500°C to 550°C. When the second sintering temperature is within this range, the resulting Na4Fe3(PO4)2(P2O7) particles can have higher conductivity and produce fewer low-activity impurity phases, resulting in higher energy density.

[0141] Optionally, the second sintering time can range from 2 hours to 48 hours. Specifically, the second sintering time can be, but is not limited to, 2 hours, 4 hours, 8 hours, 12 hours, 16 hours, 20 hours, 24 hours, 28 hours, 32 hours, 36 hours, 40 hours, 44 hours, 48 ​​hours, etc. If the second sintering time is too short, the crystallinity of the resulting second active particles will be too low, resulting in poor electrical performance; in addition, the carbonization degree of the second carbon source will decrease, reducing the conductivity of the second active particles. If the second sintering time is too long, Na4Fe3(PO4)2(P2O7) (the second active particles) will undergo phase separation, easily generating low-activity impurity phases, reducing the energy density of the second active particles, and consequently reducing the energy density of the battery when applied to a battery.

[0142] In some embodiments, during S203, when the first active particle is mixed with the second active particle, the mass ratio w of the second active particle to the first active particle is in the range of 1.5 ≤ w ≤ 4.

[0143] Specifically, the mass ratio w of the second active particle to the first active particle can be, but is not limited to, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4, etc. In this embodiment, if the mass ratio w of the second active particle to the first active particle is too small, it means that the proportion of the second active particle is too small and the proportion of the first active particle is too large. In this case, the gaps after the second active particle is stacked are not enough to fill all the first active particles, and the excess first active particles are stacked separately, reducing the compaction density of the positive electrode active material. If the mass ratio w of the second active particle to the first active particle is too large, it means that the proportion of the second active particle is too large and the proportion of the first active particle is too small. In this case, there are more gaps after the second active particle is stacked, and there are not enough second active particles to fill the gaps left after the first active particle is stacked, which will still reduce the compaction density of the positive electrode active material. When the mass ratio w of the second active particle to the first active particle is in the range of 1.5≤w≤4, the ratio of the first active particle to the second active particle is more appropriate. The first active particle can fill the gaps after the second active particle is stacked, so that the positive electrode active material has a high compaction density, and thus the battery has a high energy density when the positive electrode active material is applied to the battery.

[0144] Optionally, the first active particles and the second active particles can be mixed using a mixer such as a ball mill or a tube mixer.

[0145] When mixing the first active particles and the second active particles, the mixing speed can be from 200 rpm to 800 rpm (e.g., 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, etc.), and the mixing time can be from 2 h to 48 h (e.g., 2 h, 4 h, 8 h, 12 h, 16 h, 20 h, 24 h, 28 h, 32 h, 36 h, 40 h, 44 h, 48 h, etc.).

[0146] The positive electrode active material of this application will be further described below through specific embodiments.

[0147] Example 1

[0148] The positive electrode active material in this embodiment is prepared through the following steps:

[0149] (1) Preparation of the first active particles, including: stirring 178 g of sodium pyrophosphate (i.e., the first sodium source and the first phosphorus source), 145 g of ammonium dihydrogen phosphate (the first phosphorus source), 346 g of ferrous oxalate dihydrate (the first iron source), 20 g of glucose and 2.5 kg of water into a uniform slurry; spray drying at 105 °C to obtain the first precursor powder; placing the first precursor powder in a sintering furnace, under nitrogen protection, at a sintering temperature of 550 °C for 24 h, and cooling to obtain the first active particles (i.e. small particles Na4Fe3(PO4)2(P2O7));

[0150] (2) Preparation of the second active particles, including: stirring 172 g of sodium pyrophosphate (i.e., the second sodium source and the second phosphorus source), 146 g of ammonium dihydrogen phosphate (the second phosphorus source), 330 g of ferrous oxalate dihydrate (the second iron source), 20 g of glucose and 2.5 kg of water into a uniform slurry; spray drying at 105 °C to obtain the second precursor powder; placing the second precursor powder in a sintering furnace, under nitrogen protection, at a sintering temperature of 550 °C for 24 h, and cooling to obtain the second active particles (i.e., large particles Na4Fe3(PO4)2(P2O7));

[0151] (3) The second active particles and the first active particles are mixed in a tank mixer at a mass ratio of 6:4, at a speed of 400 rpm for 12 hours. After the mixing is completed, high-pressure compacted Na4Fe3(PO4)2(P2O7) powder (i.e. positive electrode active material) can be obtained.

[0152] Examples 2 to 7, Comparative Examples 1 to 6

[0153] The difference between Examples 2 to 7, Comparative Examples 1 to 6 and Example 1 lies in the different raw material ratios or the mass ratio w of the second active particle to the first active particle, as detailed in Table 1 below.

[0154] The particle size distribution parameters of the first active particles, second active particles, and positive electrode active materials prepared in each embodiment and comparative example are shown in Table 2 and Table 3.

[0155] The powder compaction density and positive electrode sheet compaction density of the positive electrode active materials of each embodiment and comparative example were tested, and the test results are shown in Table 3 below.

[0156] (1) Powder compaction density test method: Take 2g to 3g of Na4Fe3(PO4)2(P2O7) powder and add it into a mold with a diameter of 13mm. After pressing to 3 tons, hold the pressure for 10s and then release the pressure. Measure the mass and volume of the compressed cylinder and calculate the powder compaction density.

[0157] (2) Test method for compaction density of positive electrode sheet: Measure the thickness and mass of 12mm aluminum foil disc, then measure the thickness of the positive electrode sheet made from the positive active material of each embodiment and comparative example, cut the positive electrode sheet into 12mm discs and weigh them, thereby calculating the mass and volume of the positive active material on the positive electrode sheet, and then calculating the compaction density of the positive active material after it is made into a positive electrode sheet. The powder compaction density and electrode layer compaction density of the positive active material of each embodiment and comparative example are shown in Table 3 below.

[0158] Table 1. Parameters of the first active particle, second active particle, and positive electrode active material in each embodiment and comparative example.

[0159]

[0160] Table 2 Particle size distribution of the first and second active particles

[0161]

[0162]

[0163] Table 3. Particle size distribution, powder compaction density, and electrode layer compaction density of positive electrode active materials

[0164]

[0165] As shown in Tables 2 and 3, when 0.3 ≤ r1 ≤ 0.8 (as in Examples 1 to 7), the positive electrode active material has a high powder compaction density and electrode layer compaction density. When r1 is too small (e.g., Comparative Examples 1, 4, and 6), both the powder compaction density and electrode layer compaction density of the positive electrode active material decrease. This is because there are too few first active particles and too many second active particles, resulting in too many gaps formed after the second active particles accumulate. There are not enough first active particles to fill the gaps left by the second active particles, thus reducing the compaction density of the positive electrode active material. When r1 is too large (e.g., Comparative Examples 2, 3, and 5), both the powder compaction density and electrode layer compaction density of the positive electrode active material also decrease. This is because there are too many first active particles and too few second active particles, resulting in too few gaps formed after the second active particles accumulate. There are not enough gaps to accommodate the first active particles, and the excess first active particles accumulate alone, also reducing the compaction density of the positive electrode active material.

[0166] The test data in Tables 2 and 3 show that when 0.4 ≤ r2 ≤ 0.7, the positive electrode active material has a high powder compaction density and electrode layer compaction density. When r2 is too small, both the powder compaction density and electrode layer compaction density of the positive electrode active material will decrease; when r2 is too large, both the powder compaction density and electrode layer compaction density of the positive electrode active material will also decrease.

[0167] The test data in Tables 2 and 3 show that when 0.2 ≤ r3 ≤ 0.4, the positive electrode active material has a high powder compaction density and electrode layer compaction density. When r3 is too small, both the powder compaction density and electrode layer compaction density of the positive electrode active material will decrease; when r3 is too large, both the powder compaction density and electrode layer compaction density of the positive electrode active material will also decrease.

[0168] As shown in Tables 2 and 3, when the minimum particle size D'min of the first active particle is 0.1 μm ≤ D'min ≤ 0.8 μm; the median particle size D'50 of the first active particle is 0.5 μm ≤ D'50 ≤ 3 μm; the maximum particle size D'max of the first active particle is 1.2 μm ≤ D'max ≤ 5 μm; the minimum particle size D”min of the second active particle is 0.6 μm ≤ D”min ≤ 1.3 μm; the median particle size D”50 of the second active particle is 5 μm ≤ D”50 ≤ 8 μm; and the maximum particle size D”max of the second active particle is 32 μm ≤ D”max ≤ 38 μm, the obtained positive electrode active material has a high powder compaction density and electrode layer compaction density. Distributions of the first or second active particles exceeding these ranges will reduce the powder compaction density and electrode layer compaction density of the positive electrode active material.

[0169] As shown in Tables 2 and 3, when the particle size distribution of the positive electrode active material satisfies the following conditions: 0.1μm≤Dmin≤1.8μm, 2.2μm≤D10≤6.2μm, 8.3μm≤D50≤21.7μm, 23.1μm≤D90≤29.2μm, and 30.7μm≤Dmax≤36.9μm, the positive electrode active material has a high powder compaction density and electrode layer compaction density. Exceeding this range will reduce the powder compaction density and electrode layer compaction density of the positive electrode active material.

[0170] As shown in Tables 1 and 3, when the molar ratio A1 of sodium to phosphorus in the first active particle is 1.021 ≤ A1 ≤ 1.05, and the molar ratio B1 of iron to phosphorus in the first active particle is 0.735 ≤ B1 ≤ 0.748, the positive electrode active material has a high powder compaction density and electrode layer compaction density. This is because when the sodium-phosphorus ratio and iron-phosphorus ratio of the first active particle satisfy this relationship, the prepared first active particle can have a suitable particle size distribution. After being compounded with the second active particle, the positive electrode active material can have an even higher powder compaction density and electrode layer compaction density.

[0171] As shown in Tables 1 and 3, when the molar ratio A2 of sodium to phosphorus in the second active particle is 1.002 ≤ A2 ≤ 1.018 and the molar ratio B2 of iron to phosphorus in the second active particle is 0.705 ≤ B2 ≤ 0.73, the positive electrode active material has a high powder compaction density and electrode layer compaction density. This is because when the sodium-phosphorus ratio and iron-phosphorus ratio of the second active particle satisfy this relationship, the prepared second active particle can have a suitable particle size distribution. After being compounded with the first active particle, the positive electrode active material can have a higher powder compaction density and electrode layer compaction density.

[0172] As can be seen from the test data in Tables 1 and 3, when the mass ratio w of the second active particle to the first active particle in the positive electrode active material is in the range of 1.5≤w≤4, the positive electrode active material can have a high powder compaction density and electrode layer compaction density; if the mass ratio w of the second active particle to the first active particle is too large or too small, it will reduce the powder compaction density and electrode layer compaction density of the positive electrode active material.

[0173] Please see Figure 3 and Figure 4 This application also provides a battery 300, which includes an electrolyte; a positive electrode 310, the positive electrode 310 including the positive electrode active material of this application embodiment, the positive electrode 310 being immersed in the electrolyte; a separator 320 located on one side of the positive electrode 310 and immersed in the electrolyte; and a negative electrode 330 disposed on the side of the separator 320 opposite to the positive electrode 310 and immersed in the electrolyte.

[0174] The battery 300 in this application embodiment can be, but is not limited to, a sodium-ion battery 300.

[0175] Understandably, the positive electrode 310, the separator 320, and the negative electrode 330 are sequentially stacked to form an electrode assembly. The electrode assembly can be, but is not limited to, a wound structure, a stacked structure, etc., and this application does not specifically limit it in this regard.

[0176] Optionally, the electrolyte may include, but is not limited to, solvents and electrolyte salts.

[0177] Please see Figure 5 Optionally, the positive electrode 310 includes a positive current collector 311 and a positive active layer 312. The positive current collector 311 can be, but is not limited to, aluminum foil or aluminum sheet. The positive active layer 312 includes the aforementioned positive active material, a first conductive agent, a first binder, and a first thickener, etc.

[0178] Please see Figure 6 Optionally, the negative electrode 330 includes a negative electrode current collector 331 and a negative electrode active layer 332. The negative electrode current collector 331 can be, but is not limited to, copper foil or copper sheet. The negative electrode active layer 332 includes a negative electrode active material, a second conductive agent, a second binder, and a second thickener, etc.

[0179] Optionally, the diaphragm 320 can be, but is not limited to, at least one of polypropylene membrane (PP membrane), polyethylene membrane (PE membrane), ceramic diaphragm 320, etc.

[0180] Optionally, the battery 300 further includes a housing 340 and an end cap assembly 350, the housing 340 and the end cap assembly 350 forming a closed receiving cavity (not shown) for housing the electrolyte, the positive electrode 310, the separator 320, and the negative electrode 330. Understandably, the end cap assembly 350 electrically connects the positive electrode 310 and the negative electrode 330, respectively, and leads out the positive electrode 310 and the negative electrode 330 for electrical connection to external devices or other batteries 300.

[0181] In this application, the terms "embodiment" and "implementation" mean that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of these phrases in various locations throughout the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this application can be combined with other embodiments. Furthermore, it should be understood that the features, structures, or characteristics described in the various embodiments of this application can be arbitrarily combined to form yet another embodiment that does not depart from the spirit and scope of the technical solution of this application, provided there is no contradiction between them.

[0182] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. A positive electrode active material, characterized in that, The material includes a first active particle and a second active particle, wherein the average particle size of the first active particle is smaller than the average particle size of the second active particle; on the particle size distribution curve of the positive electrode active material, the first active particle has a first peak and the second active particle has a second peak, and the ratio r1 of the peak value of the first peak to the peak value of the second peak is in the range of 0.3≤r1≤0.8; both the first active particle and the second active particle are sodium iron pyrophosphate; the molar ratio A1 of sodium and phosphorus in the first active particle is in the range of 1.021≤A1≤1.05; and the molar ratio B1 of iron and phosphorus in the first active particle is in the range of 0.735≤B1≤0.

748.

2. The positive electrode active material according to claim 1, characterized in that, The ratio r2 of the valley between the first peak and the second peak to the peak value of the first peak is in the range of 0.4≤r2≤0.

7.

3. The positive electrode active material according to claim 1, characterized in that, The ratio r3 of the valley between the first peak and the second peak to the peak value of the second peak is in the range of 0.2≤r3≤0.

4.

4. The positive electrode active material according to claim 1, characterized in that, The minimum particle size D'min of the first active particle ranges from 0.1 μm to 0.8 μm; the median particle size D'50 of the first active particle ranges from 0.5 μm to 3 μm; the maximum particle size D'max of the first active particle ranges from 1.2 μm to 5 μm; the minimum particle size D''min of the second active particle ranges from 0.6 μm to 1.3 μm; the median particle size D''50 of the second active particle ranges from 5 μm to 8 μm; and the maximum particle size D''max of the second active particle ranges from 32 μm to 38 μm.

5. The positive electrode active material according to claim 1, characterized in that, The particle size distribution of the positive electrode active material satisfies the following: 0.1μm≤Dmin≤1.8μm, 2.2μm≤D10≤6.2μm, 8.3μm≤D50≤21.7μm, 23.1μm≤D90≤29.2μm, 30.7μm≤Dmax≤36.9μm, where Dmin is the minimum particle size of the positive electrode active material, D10 is the particle size corresponding to a cumulative particle size distribution percentage of 10% for the positive electrode active material, D50 is the particle size corresponding to a cumulative particle size distribution percentage of 50% for the positive electrode active material, D90 is the particle size corresponding to a cumulative particle size distribution percentage of 90% for the positive electrode active material, and Dmax is the maximum particle size of the positive electrode active material.

6. The positive electrode active material according to claim 1, characterized in that, In the positive electrode active material, the mass ratio w of the second active particle to the first active particle is in the range of 1.5≤w≤4.

7. The positive electrode active material according to any one of claims 1-6, characterized in that, The molar ratio A2 of sodium and phosphorus in the second active particle is in the range of 1.002≤A2≤1.018; the molar ratio B2 of iron and phosphorus in the second active particle is in the range of 0.705≤B2≤0.

73.

8. The positive electrode active material according to any one of claims 1-6, characterized in that, The molar ratio A of sodium to phosphorus in the positive electrode active material is in the range of 1.008 ≤ A ≤ 1.04; the molar ratio B of iron to phosphorus in the positive electrode active material is in the range of 0.714 ≤ B ≤ 0.

748.

9. A method for preparing a positive electrode active material, characterized in that, include: The preparation of the first active particles includes: providing a first sodium source, a first phosphorus source, a first iron source, and a first carbon source; stirring and mixing the first sodium source, the first phosphorus source, the first iron source, and the first carbon source in a solvent to obtain a first slurry, and performing a first spray drying to obtain a first precursor powder; and performing a first sintering on the first precursor powder to obtain the first active particles, wherein the first active particles are sodium iron pyrophosphate. The preparation of second active particles includes: providing a second sodium source, a second phosphorus source, a second iron source, and a second carbon source; mixing the second sodium source, the second phosphorus source, the second iron source, and the second carbon source in a solvent to obtain a second slurry, and then performing a second spray drying to obtain a second precursor powder; and performing a second sintering on the second precursor powder to obtain the second active particles, wherein the second active particles are sodium iron pyrophosphate, and the average particle size of the first active particles is smaller than the average particle size of the second active particles; and The first active particle and the second active particle are mixed to obtain the positive electrode active material, wherein the first active particle has a first peak and the second active particle has a second peak on the particle size distribution curve of the positive electrode active material, and the ratio r1 of the peak value of the first peak to the peak value of the second peak is in the range of 0.3≤r1≤0.8; both the first active particle and the second active particle are sodium iron pyrophosphate; the molar ratio A1 of sodium and phosphorus in the first active particle is in the range of 1.021≤A1≤1.05; and the molar ratio B1 of iron and phosphorus in the first active particle is in the range of 0.735≤B1≤0.

748.

10. The method for preparing the positive electrode active material according to claim 9, characterized in that, When preparing the first active particles, the molar ratio A1 of sodium to phosphorus in the first sodium source, the first phosphorus source and the first iron source is in the range of 1.021≤A1≤1.05, and the molar ratio B1 of iron to phosphorus is in the range of 0.735≤B1≤0.

748.

11. The method for preparing the positive electrode active material according to claim 9, characterized in that, When preparing the second active particles, the molar ratio A2 of sodium to phosphorus in the second sodium source, the second phosphorus source and the second iron source is in the range of 1.002≤A2≤1.018; the molar ratio B2 of iron to phosphorus is in the range of 0.705≤B2≤0.

73.

12. The method for preparing the positive electrode active material according to any one of claims 9-11, characterized in that, In the positive electrode active material, the mass ratio w of the second active particle to the first active particle is in the range of 1.5≤w≤4.

13. The method for preparing the positive electrode active material according to any one of claims 9-11, characterized in that, The solid content of the first slurry ranges from 20% to 40%; the temperature during the first spray drying ranges from 95°C to 120°C; and the temperature during the first sintering ranges from 450°C to 620°C. The solid content of the second slurry ranges from 20% to 40%; the temperature during the second spray drying ranges from 95°C to 120°C; and the temperature during the second sintering ranges from 450°C to 620°C.

14. A battery, characterized in that, include: Electrolyte; A positive electrode sheet, wherein the positive electrode sheet comprises the positive active material according to any one of claims 1-8 or the positive active material prepared by the preparation method of the positive active material according to any one of claims 9-13; A diaphragm is located on one side of the positive electrode plate, and The negative electrode is disposed on the side of the diaphragm opposite to the positive electrode.

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