Prussian blue-based positive electrode material, preparation method thereof, positive electrode sheet, sodium ion battery and electric device

Abstract

This invention discloses a Prussian blue-based cathode material and its preparation method, a cathode sheet, a sodium-ion battery, and an electrical device, relating to the field of sodium-ion battery cathode material technology. The Prussian blue-based cathode material comprises a first and a second particle with a bimodal particle size distribution and a reasonable ratio. The smaller particle size fills the gaps between the larger particles, significantly improving the material's tap density and structural stability, providing a material basis for the development of high-energy-density, high-power sodium-ion batteries. The bimodal particle size distribution also alleviates volume expansion stress during battery charging and discharging, reduces the risk of particle breakage, and improves the battery's cycle life. The preparation method uses a two-stage feeding process to control the feed solution concentration, precisely regulating the crystal growth kinetics of Prussian blue crystals at different stages, thereby obtaining a mixed particle material with a specific particle size ratio, providing a novel technical path for optimizing the performance of Prussian blue cathode materials.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery cathode material technology, and more specifically, to Prussian blue cathode materials and their preparation methods, cathode sheets and sodium-ion batteries, and electrical devices. Background Technology

[0002] Prussian blue cathode materials (such as Na2Fe[Fe(CN)6]) have become a research hotspot for sodium-ion battery cathode materials due to their advantages such as three-dimensional open framework structure, high theoretical capacity (about 170 mAh / g) and low-cost raw materials. Currently, the particle size distribution of commercial and research-developed Prussian blue cathode materials is relatively narrow. Although this single particle size distribution can ensure the performance of the material in specific scenarios, it has the following limitations: (1) There is a bottleneck in improving the tap density: the proportion of voids between uniform small particles is high, and the tap density is difficult to break through 0.5 g / cm. 3 (2) Insufficient scene adaptability: It cannot simultaneously meet the differentiated needs of high-rate discharge and high energy density.

[0003] Improving the problem of uniform particle size and poor application adaptability of Prussian blue cathode materials has become one of the technical challenges that urgently need to be addressed in this field.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide Prussian blue-based cathode materials and their preparation methods, cathode sheets, sodium-ion batteries, and electrical devices, in order to solve or improve the aforementioned technical problems.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a Prussian blue cathode material, which includes a first particle and a second particle with a bimodal particle size distribution, wherein the particle size D50 of the first particle is 3μm-8μm and the particle size D50 of the second particle is 0.5μm-3μm. The tap density of Prussian blue-based cathode materials is ≥0.5 g / cm³. 3 .

[0007] Secondly, the present invention provides a method for preparing a Prussian blue-type cathode material according to any of the foregoing embodiments, comprising the following steps: The first ferrocyanide solution and the first transition metal salt solution were added to the base solution respectively, and the reaction was carried out for 1 to 4 hours to obtain the first system. The second ferrocyanide solution and the second transition metal salt solution were added to the first system, and the reaction was continued for 2-6 hours to obtain the second system. After washing, filtering and drying the slurry of the second system, Prussian blue cathode material is obtained. Wherein, the concentration of the first ferrocyanide solution is less than the concentration of the second ferrocyanide solution, and the concentration of the first transition metal salt solution is less than the concentration of the second transition metal salt solution.

[0008] Thirdly, the present invention provides a positive electrode sheet, comprising a Prussian blue positive electrode material as described in any of the foregoing embodiments or a Prussian blue positive electrode material prepared by any of the foregoing embodiments.

[0009] Fourthly, the present invention provides a sodium-ion battery, including a positive electrode as described in the foregoing embodiments.

[0010] Fifthly, the present invention provides an electrical device including the sodium-ion battery of the aforementioned embodiments.

[0011] The present invention has the following beneficial effects: The Prussian blue cathode material provided in this invention features a bimodal particle size distribution. The optimal ratio of the first to the second particle size allows smaller particles to fill the gaps between larger particles, significantly improving the material's tap density and structural stability. This provides a material basis for the development of high-energy-density, high-power sodium-ion batteries. The bimodal particle size distribution can alleviate volume expansion stress during battery charging and discharging, reduce the risk of particle breakage, and improve battery cycle life.

[0012] The preparation method achieves precise control of the crystal growth kinetics of Prussian blue crystals at different stages by controlling the concentration of the feed solution through a two-stage feeding process, thereby obtaining mixed particulate materials with a specific particle size ratio, providing a new technical path for the performance optimization of Prussian blue cathode materials. Attached Figure Description

[0013] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 Here is a SEM image of Example 1; Figure 2 Here is a SEM image of Example 2; Figure 3 The image shown is a SEM image of Comparative Example 1. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0016] This invention achieves precise control of the crystal growth kinetics of Prussian blue cathode materials at different stages through a two-stage feeding process to control the feed concentration, thereby obtaining mixed particulate materials with a specific particle size ratio. This provides a novel technical approach for optimizing the performance of Prussian blue cathode materials. The bimodal particle size distribution structure of the Prussian blue cathode material significantly improves the tap density and structural stability of the material, providing a material foundation for the development of high-energy-density, high-power sodium-ion batteries. It can also alleviate the volume expansion stress during battery charging and discharging, reduce the risk of material particle breakage, and improve the cycle life of the battery. The specific implementation process is analyzed as follows: In a first aspect, the present invention provides a Prussian blue cathode material, which includes a first particle and a second particle with a bimodal particle size distribution, wherein the particle size D50 of the first particle is 3μm-8μm and the particle size D50 of the second particle is 0.5μm-3μm. The tap density of Prussian blue-based cathode materials is ≥0.5 g / cm³. 3 .

[0017] It should be noted that in the Prussian blue cathode material provided by this invention, the first particle is a large-diameter particle. Its rounded crystal structure and low specific surface area effectively improve the overall compaction density of the electrode, ensuring the structural stability and low interfacial impedance of the material. The second particle is a small-diameter particle, which can fully fill the gaps between the first particles, significantly reducing the porosity inside the electrode and providing more active reaction sites, ultimately achieving close packing of material particles at the microscale. Through the synergistic effect of the large-diameter and small-diameter particles, the electrode compaction density is improved compared to conventional single-particle-size materials, laying a core foundation for achieving high energy density.

[0018] The Prussian blue cathode material provided by this invention has a particle packing structure with a bimodal particle size distribution that can alleviate the volume expansion stress during battery charging and discharging, reduce the risk of material particle breakage, and improve the cycle life of the battery.

[0019] For example, the tap density of the Prussian blue-type cathode material is selected from 0.5 g / cm³. 3 0.6g / cm 3 0.7g / cm 3 0.8g / cm 3 0.9g / cm 31.0g / cm 3 Any one of them.

[0020] In an optional embodiment, the particle size D50 of the first particle is 3μm-8μm, and the particle size D50 of the second particle is 0.5μm-3μm.

[0021] In an optional embodiment, the morphology of the first particle and the second particle is independently either spherical or square; And / or, the chemical formula of Prussian blue-type cathode materials is Na x Mn y Fe 1-y [Fe(CN)6], 0<x≤2, 0≤y≤1.

[0022] It should be noted that in the above general formula, x represents the number of sodium ion sites occupied, and y represents the molar percentage of manganese in the transition metal sites. Adjusting the values ​​of x and y can achieve precise control of material capacity, voltage plateau and cycle stability.

[0023] Secondly, the present invention provides a method for preparing a Prussian blue-type cathode material according to any of the foregoing embodiments, comprising the following steps: The first ferrocyanide solution and the first transition metal salt solution were added to the base solution respectively, and the reaction was carried out for 1 to 4 hours to obtain the first system. The second ferrocyanide solution and the second transition metal salt solution were added to the first system, and the reaction was continued for 2-6 hours to obtain the second system. After washing, filtering and drying the slurry of the second system, Prussian blue cathode material is obtained. Wherein, the concentration of the first ferrocyanide solution is less than the concentration of the second ferrocyanide solution, and the concentration of the first transition metal salt solution is less than the concentration of the second transition metal salt solution.

[0024] It should be noted that the concentration of the first ferrocyanide solution is less than that of the second ferrocyanide solution, and the concentration of the first transition metal salt solution is less than that of the second transition metal salt solution. The significance of this setting is that when the former concentration is lower, fewer crystal nuclei are formed, providing the necessary conditions for the subsequent growth of crystal nuclei into larger particles. If the order is reversed, a large number of crystal nuclei are formed in the early stage, making it difficult for subsequent crystal nuclei to grow, and the crystal nuclei size is difficult to distinguish, making it impossible to generate materials with a bimodal particle size distribution.

[0025] The present invention does not specifically limit the reaction equipment, and it is reasonably selected according to the actual amount of material being processed. Specifically, in the embodiments of the present invention, the reaction equipment used is a reaction vessel.

[0026] Washing, filtration, and drying processes can be selected according to actual needs, and this invention does not impose any particular limitations. Specifically, in the embodiments of this invention, deionized water is used for washing, and the slurry is washed 3-5 times; pressure filtration is used for filtration; and vacuum drying is used for drying.

[0027] In an optional embodiment, the concentration of the first ferrocyanide solution is 0.2 mol / L-0.5 mol / L, the concentration of the second ferrocyanide solution is 0.8 mol / L-1.2 mol / L, the concentration of the first transition metal salt solution is 0.8 mol / L-1.0 mol / L, and the concentration of the second transition metal salt solution is 1.0 mol / L-2.0 mol / L.

[0028] For example, the concentration of the first ferrocyanide solution is selected as needed from any one of 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, and 0.5 mol / L, or other values ​​within the range of 0.2 mol / L to 0.5 mol / L. The concentration of the second ferrocyanide solution is selected as needed from any one of 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, and 1.2 mol / L, or other values ​​within the range of 0.8 mol / L to 1.2 mol / L. The concentration of the first transition metal salt solution is selected as needed from any one of 0.8 mol / L, 0.9 mol / L, and 1.0 mol / L, or other values ​​within the range of 0.8 mol / L to 1.0 mol / L. The concentration of the second transition metal salt solution may be selected from any one of 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L and 2.0 mol / L, or other values ​​in the range of 1.0 mol / L to 2.0 mol / L, as needed.

[0029] In an optional embodiment, the amounts of the first ferrocyanide solution and the second ferrocyanide solution are each independently selected from 18L to 23L, and the amounts of the first transition metal salt solution and the second transition metal salt solution are each independently selected from 10L to 20L.

[0030] For example, the amounts of the first ferrocyanide solution and the second ferrocyanide solution are independently selected from any one of 18L, 19L, 20L, 21L, 22L, and 23L, or other values ​​within the range of 18L-23L, according to actual needs. The amounts of the first transition metal salt solution and the second transition metal salt solution are independently selected from any one of 10L, 11L, 12L, 13L, 15L, 16L, 17L, 18L, and 20L, or other values ​​within the range of 10L-20L, according to actual needs.

[0031] In an optional implementation, the amount of base liquid used is 8L-15L; for example, the amount of base liquid used is selected from any one of 8L, 9L, 10L, 11L, 12L, 13L, 14L and 15L, or other values ​​within the range of 8L-15L, depending on actual needs.

[0032] In an optional embodiment, the base solution includes a complexing agent with a concentration of 1.0 mol / L to 2.0 mol / L and a sodium supplement with a concentration of 1.0 mol / L to 2.0 mol / L.

[0033] For example, the concentration of the complexing agent may be selected as needed from any one of 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.7 mol / L, 1.8 mol / L, and 2.0 mol / L, or other values ​​within the range of 1.0 mol / L to 2.0 mol / L. The concentration of the sodium supplement may be selected as needed from any one of 1.0 mol / L, 1.2 mol / L, 1.3 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, and 2.0 mol / L, or other values ​​within the range of 1.0 mol / L to 2.0 mol / L.

[0034] It should be noted that complexing agents can react with transition metal ions (such as Fe) in the reaction system solution. 2+ Mn 2+ Ni 2+ (e.g., ferrocyanide ions) form soluble complexes, slowly releasing transition metal ions, thereby controlling the reaction rate with ferrocyanide ions and achieving uniform, slow co-precipitation. Appropriate amounts of complexing agents can effectively control nucleation and growth rates, producing materials with good crystallinity, small and uniform particle size, and regular morphology (such as cubic nanoparticles). This is beneficial for improving the tap density, sodium ion diffusion rate, and structural integrity of the material, thus achieving excellent rate performance and cycling stability.

[0035] If the amount of complexing agent added is too small, the complexing effect will be insufficient, the precipitation reaction will be too rapid, and materials with poor crystallinity, large particles, and irregular morphology (such as blocky agglomerates) will easily be formed. The vacancy and water of crystallization content in the material may be high, resulting in poor structural stability and poor cycling performance. If the amount of complexing agent added is too large, the reaction will be excessively inhibited, which may lead to a decrease in yield or the formation of amorphous or poorly crystallized products. Excessive organic complexing agent residue may also introduce impurity carbon during subsequent calcination, affecting electrochemical performance.

[0036] In an optional embodiment, the complexing agent is selected from at least one of sodium hexametaphosphate, triethanolamine, sodium citrate, ascorbic acid, tartaric acid, glucose, or ethylenediaminetetraacetic acid.

[0037] In an optional embodiment, the salt type of the transition metal salt is independently selected from at least one of sulfate, nitrate, acetate or chloride; and the transition metal is independently selected from at least one of Mn, Fe, Ni, Co, Cu or Zn.

[0038] It should be noted that the types of the first and second transition metal salts can be reasonably selected according to actual needs. The two transition metal salt solutions can be the same transition metal and the same salt type, or the same transition metal and different salt types, or different transition metals and different salt types.

[0039] In an optional embodiment, the ferrocyanide is selected from sodium ferrocyanide or potassium ferrocyanide.

[0040] Thirdly, the present invention provides a positive electrode sheet, comprising a Prussian blue positive electrode material as described in any of the foregoing embodiments or a Prussian blue positive electrode material prepared by any of the foregoing embodiments.

[0041] Fourthly, the present invention provides a sodium-ion battery, including a positive electrode as described in the foregoing embodiments.

[0042] Fifthly, the present invention provides an electrical device including the sodium-ion battery of the aforementioned embodiments.

[0043] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0044] Example 1 This embodiment provides a method for preparing a Prussian blue-based cathode material, including the following steps: (1) The first ferrocyanide solution (sodium ferrocyanide solution, concentration 0.3 mol / L, volume 20 L) and the first transition metal salt solution (manganese sulfate / ferrous sulfate mixed solution, Mn / Fe molar ratio 1:1, concentration 0.9 mol / L, volume 4 L) were added to 10 L of the bottom solution respectively. The reaction system was placed in a reaction vessel and reacted at 50 °C for 1.5 hours to obtain the first system. The bottom solution included a complexing agent (sodium citrate) with a concentration of 1.7 mol / L and a sodium supplement agent (sodium sulfate) with a concentration of 1.0 mol / L.

[0045] (2) The second ferrocyanide solution (sodium ferrocyanide solution, concentration 0.6 mol / L, volume 15 L) and the second transition metal salt solution (manganese sulfate / ferrous sulfate mixed solution, Mn / Fe molar ratio 1:1, concentration 1.5 mol / L, volume 4 L) were added to the first system obtained in step (1), and the reaction was continued at 50 °C for 2.5 hours to obtain the second system; (3) After washing, filtering and drying the slurry of the second system obtained in step (2), Prussian blue cathode material with the chemical formula Na is obtained. 1.7 Mn 0.5 Fe 0.5 [Fe(CN)6]; the washing process involves washing the slurry with deionized water 3-5 times, the filtration process involves pressure filtration, and the drying process involves vacuum drying.

[0046] Example 2 This embodiment provides a method for preparing a Prussian blue-based cathode material, which differs from Example 1 only in that it includes the following steps: (1) The first ferrocyanide solution (sodium ferrocyanide, 0.3 mol / L, 20 L) and the first transition metal salt solution (manganese sulfate and ferrous sulfate mixed in a molar ratio of 1:1, 0.3 mol / L, 4 L) were added to 50 L of the base solution respectively, and reacted at 60 °C for 4 hours to obtain the first system; wherein, the concentrations of complexing agent and sodium supplement in the base solution were completely consistent with those in Example 1; (2) The second ferrocyanide solution (sodium ferrocyanide, 0.6 mol / L, 15 L) and the second transition metal salt solution (manganese sulfate and ferrous sulfate mixed in a molar ratio of 1:1, 0.6 mol / L, 4 L) were added to the first system obtained in step (1), and the reaction was continued at 60 °C for 6 hours to obtain the second system. (3) The washing, filtering, and drying post-processing parameters are completely consistent with those in Example 1, and the Prussian blue cathode material is finally obtained, with the chemical formula Na. 1.7 Mn 0.5 Fe 0.5 [Fe(CN)6], corresponding to a first particle D50 of 4.2 μm and a second particle D50 of 1.2 μm.

[0047] Comparative Example 1 This comparative example provides a single-particle-size Prussian blue cathode material, which is prepared using a conventional one-step co-precipitation method, including the following steps: (1) Preparation of ferrocyanide solution: Weigh sodium ferrocyanide decahydrate (purity 99%), dissolve it in deionized water, and make up to 30L to obtain a ferrocyanide solution with a concentration of 0.6mol / L; (2) Preparation of transition metal salt solution: Weigh manganese sulfate monohydrate (purity 98%) and ferrous sulfate heptahydrate (purity 98%), mix them evenly in a molar ratio of 1:1 and dissolve them in deionized water, and make up to 10L to obtain a transition metal salt solution with a total metal ion concentration of 1.5mol / L. (3) Preparation of the base solution: Deionized water, sodium citrate (complexing agent) and sodium sulfate (sodium supplement) are added sequentially to a 50L reactor and stirred until completely dissolved to obtain the base solution. The concentration of the complexing agent is 50g / L and the concentration of the sodium supplement is 195g / L, which is completely consistent with the base solution parameters of Example 1. (4) Coprecipitation reaction: The ferrocyanide solution from step (1) and the transition metal salt solution from step (2) are simultaneously and uniformly added dropwise to the bottom liquid of the reaction vessel; (5) Post-processing: After the reaction, the product slurry was filtered, washed three times with deionized water and once with ethanol, and then placed in a vacuum drying oven and dried at 80°C for 12 hours to obtain a single-particle-size Prussian blue cathode material with the chemical formula Na. 1.7 Mn 0.5 Fe 0.5 [Fe(CN)6], D50 is 5.0 μm.

[0048] Test Example 1 This test case was used to investigate the particle size distribution of the products obtained in Example 1, Example 2 and Comparative Example 1. The test was conducted using a laser particle size analyzer. The span was also summarized, with span = (D90-D10) / D50, which is used to characterize the width of the particle size distribution. The larger the value, the wider the particle size distribution. The relevant results are shown in Table 1.

[0049] Table 1 Test Results

[0050] As can be seen from the data in Table 1, the Prussian blue cathode materials prepared in Examples 1 and 2 both exhibit obvious bimodal particle size distributions, with span values ​​significantly higher than those of the single-particle-size Comparative Example 1. The tap density is more than 34% higher than that of Comparative Example 1, indicating that small particles can effectively fill the gaps between large particles, significantly increasing the packing density of the material, which is beneficial to improving the volumetric energy density of the battery.

[0051] Test Example 2 This test example analyzes the tap density of the Prussian blue cathode materials prepared in Example 1, Example 2 and Comparative Example 1. The relevant results are shown in Table 1.

[0052] As can be seen from the data in Table 1, the tap densities of Example 1 and Example 2 reached 0.85 g / cm³ and 0.78 g / cm³, respectively, which are 63.5% and 50% higher than the 0.52 g / cm³ of Comparative Example 1, respectively. This verifies the significant effect of the bimodal particle size packing structure on improving the tap density of the material. At the same time, as the concentration of the feed solution in both stages increases, the overall particle size of the prepared material decreases, and the tap density decreases slightly. This indicates that by adjusting the feed solution concentration parameters in the co-precipitation process, the tap density can be controllably adjusted in the range of 0.7 g / cm³-0.9 g / cm³, adapting to the different energy density requirements of different battery systems.

[0053] Test Example 3 This test example examines the electrochemical performance of the Prussian blue cathode materials prepared in Examples 1, 2, and Comparative Example 1. The prepared cathode materials were mixed with conductive agent Super P and binder PVDF at a mass ratio of 8:1:1 to prepare cathode sheets. CR2032 coin cells were assembled using metallic sodium as the negative electrode, and charge-discharge tests were conducted in the voltage range of 2.0V-4.0V. The relevant results are shown in Table 2.

[0054] Table 2 Electrochemical performance test results of different samples

[0055] As can be seen from the data in Table 2, compared with the single-particle-size Comparative Example 1, the sample of the example with bimodal particle size structure has significantly improved discharge specific capacity, initial coulombic efficiency and cycle stability. This indicates that the bimodal stacking structure can not only improve the tap density of the material, but also improve the ion transport dynamics inside the electrode, reduce polarization, and ultimately optimize the overall electrochemical performance.

[0056] Test Example 4 This test example analyzes the morphology of the Prussian blue cathode materials prepared in Examples 1, 2, and Comparative Example 1. The relevant results are shown in […]. Figure 1 (SEM morphology image of Example 1) Figure 2 (SEM morphology image of Example 2) Figure 3 (SEM morphology image of Comparative Example 1).

[0057] from Figure 1 and Figure 2 It can be seen that the material prepared in the examples contains both large, spherical particles of approximately 5 μm and small, square particles of 1 μm-2 μm. The small particles are uniformly filled in the gaps between the large particles, resulting in a dense overall packing. Figure 3 The comparative material has uniform particle size and obvious interparticle voids, which verifies that the two-step co-precipitation method can achieve the controllable synthesis of bimodal particle size structure, which is in complete agreement with the particle size distribution and tap density test results mentioned above.

[0058] In summary, the Prussian blue cathode material with a bimodal particle size distribution provided by this invention has the following characteristics: High tap density: By using a reasonable ratio of large to small particles, the small particles can fill the gaps between the large particles, significantly increasing the tap density of the material. Experiments show that when the ratio of large to small particles is certain, the tap density of the material is more than 30% higher than that of materials with a single particle size distribution, effectively improving the energy density of the battery.

[0059] Scenario-specific adaptability: The ratio of large to small particles can be adjusted according to different application scenarios. In scenarios with high energy density requirements, the proportion of large particles is increased to improve battery energy density by utilizing the high volumetric capacity of large particles; in scenarios with high power performance requirements, the proportion of small particles is increased to enhance the rate performance and cycle stability of the material by leveraging the advantages of short ion transport paths of small particles.

[0060] Structural stability optimization: The bimodal particle size distribution can alleviate the volume expansion stress during battery charging and discharging, reduce the risk of material particle breakage, and improve battery cycle life. Tests show that after 1000 cycles at 1C rate, the capacity retention of this material is about 15% higher than that of materials with a single particle size distribution.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A Prussian blue-based cathode material, characterized in that, The Prussian blue cathode material comprises a first particle and a second particle with a bimodal particle size distribution, wherein the particle size D50 of the first particle is 3μm-8μm and the particle size D50 of the second particle is 0.5μm-3μm. The tap density of the Prussian blue-based cathode material is ≥0.5 g / cm³. 3 .

2. The Prussian blue-based cathode material according to claim 1, characterized in that, The particle size D50 of the first particle is 3μm-8μm, and the particle size D50 of the second particle is 0.5μm-3μm.

3. The Prussian blue-based cathode material according to claim 1, characterized in that, The first particle and the second particle are independently spherical or square in shape, respectively; And / or, the chemical formula of the Prussian blue cathode material is Na x Mn y Fe 1-y [Fe(CN)6], 0<x≤2, 0≤y≤1.

4. The method for preparing Prussian blue-based cathode materials according to any one of claims 1-3, characterized in that, Includes the following steps: The first ferrocyanide solution and the first transition metal salt solution were added to the base solution respectively, and reacted at 40℃-60℃ for 1 hour to 4 hours to obtain the first system. The second ferrocyanide solution and the second transition metal salt solution were added to the first system, and the reaction was continued at 40℃-60℃ for 2-6 hours to obtain the second system. After washing, filtering and drying the slurry of the second system, Prussian blue cathode material is obtained. Wherein, the concentration of the first ferrocyanide solution is less than the concentration of the second ferrocyanide solution, and the concentration of the first transition metal salt solution is less than the concentration of the second transition metal salt solution.

5. The preparation method according to claim 4, characterized in that, The concentration of the first ferrocyanide solution is 0.2 mol / L-0.5 mol / L, the concentration of the second ferrocyanide solution is 0.8 mol / L-1.2 mol / L, the concentration of the first transition metal salt solution is 0.8 mol / L-1.0 mol / L, and the concentration of the second transition metal salt solution is 1.0 mol / L-2.0 mol / L. And / or, based on a 50L reactor, the amounts of the first ferrocyanide solution and the second ferrocyanide solution are each independently selected from 18L-23L, and the amounts of the first transition metal salt solution and the second transition metal salt solution are each independently selected from 10L-20L.

6. The preparation method according to claim 4, characterized in that, The amount of the base liquid used is 8L-15L; And / or, the base solution comprises a complexing agent with a concentration of 1.0 mol / L to 2.0 mol / L and a sodium supplement with a concentration of 1.0 mol / L to 2.0 mol / L.

7. The preparation method according to claim 4, characterized in that, The complexing agent is selected from at least one of sodium hexametaphosphate, triethanolamine, sodium citrate, ascorbic acid, tartaric acid, glucose, or ethylenediaminetetraacetic acid; And / or, the sodium supplement is selected from at least one of sodium sulfate, sodium nitrate, sodium acetate, and sodium chloride; And / or, the salt type of the transition metal salt is independently selected from at least one of sulfate, nitrate, acetate or chloride; the transition metal is independently selected from at least one of Mn, Fe, Ni, Co, Cu or Zn; And / or, the ferrocyanide is selected from sodium ferrocyanide or potassium ferrocyanide.

8. A positive electrode sheet, characterized in that, This includes the Prussian blue cathode material as described in any one of claims 1-3 or the Prussian blue cathode material prepared by the preparation method as described in any one of claims 4-7.

9. A sodium-ion battery, characterized in that, Including the positive electrode sheet as described in claim 8.

10. An electrical appliance, characterized in that, Including the sodium-ion battery as described in claim 9.

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