Prussian blue positive electrode material, and preparation method therefor and use thereof

Abstract

A Prussian blue positive electrode material, and a preparation method therefor and a use thereof. The preparation method comprises the following steps: (1) respectively freezing a portion of a sodium ferrocyanide solution and a portion of a transition metal salt solution, crushing the frozen sodium ferrocyanide solution and the frozen transition metal salt solution at a low temperature and mixing same, and pressing and freezing to obtain a frozen mixed solution; (2) mixing the other portion of the sodium ferrocyanide solution and the other portion of the transition metal salt solution at a low temperature, and then performing heating treatment to obtain a seed crystal suspension; and (3) placing the frozen mixed solution in a backflow device, controlling the seed crystal suspension to flow back between a reaction kettle and the backflow device until the frozen mixed solution is completely dissolved, and then performing aging treatment to obtain a Prussian blue positive electrode material. According to the method, the reaction rate can be controlled, so that the reaction rate is low, particle agglomeration is reduced, and the electrical performance of the material is more excellent.

Description

A Prussian blue positive electrode material and its preparation method and application Technical Field

[0001] The present disclosure belongs to the technical field of battery materials and relates to a Prussian blue positive electrode material and a preparation method and application thereof. Background Art

[0002] In recent years, with the rapid development of new energy vehicles, the demand for lithium-ion batteries has increased. However, lithium resource production is insufficient to support this demand, making the development of new electrochemical energy storage systems particularly important. Sodium ions and lithium ions have similar properties, and sodium-ion batteries have similar performance and operating principles, offering promising development prospects. However, the development of sodium-ion batteries is limited by the cathode materials used. The main sodium-ion cathode materials include layered transition metal oxides, polyanionic compounds, and Prussian blue analogs.

[0003] Prussian blue analogs are considered one of the most promising sodium-ion cathode materials due to their high theoretical specific capacity, high sodium storage potential, and excellent cycling performance. Prussian blue is typically prepared by solution coprecipitation, resulting in a product containing a high concentration of lattice water and interstitial water, which leads to incomplete sodium ion diffusion channels and reduced electrode material kinetics. One reason for the introduction of lattice water is that the coprecipitation reaction is rapid, with crystal nucleation and growth occurring almost simultaneously. This results in low crystallinity and numerous defects in the lattice, which in turn introduces lattice water. Furthermore, the rapid reaction rate of coprecipitation can lead to crystal agglomeration, which is detrimental to the release of electrochemical performance.

[0004] CN115784258A discloses a method for preparing a manganese-based Prussian blue positive electrode material, comprising the following steps: (1) first mixing sodium ferrocyanide, a first soluble sodium salt and water to obtain a first mixed solution; (2) second mixing a soluble divalent manganese salt, a second soluble sodium salt and water to obtain a second mixed solution; (3) adding the first mixed solution, the second mixed solution and a complexing agent to a soluble sodium salt solution to carry out a coprecipitation reaction to obtain the manganese-based Prussian blue positive electrode material.

[0005] CN115367772A discloses a method for preparing a Prussian blue cathode material. The method adopts a high-speed shearing method to replace the traditional magnetic stirring or mechanical stirring method, so that the entire reaction system in the coprecipitation process is as close to the ideal reaction state as possible, and each ion is evenly dispersed in the solution and complexed with each other at the same probability. At the same time, the method controls the temperature of the coprecipitation and aging process to regulate the grain nucleation and growth process, so as to obtain a Prussian blue cathode material with high crystallinity, low defects, low water content and high sodium content.

[0006] The method described in the above scheme for preparing the Prussian blue positive electrode material only regulates the nucleation and growth process of the crystal by a simple method, resulting in low crystal crystallinity and a large number of defects in the lattice, thereby introducing lattice water and causing low electrical performance.

[0007] Summary of the Invention

[0008] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0009] The purpose of the present disclosure is to provide a Prussian blue positive electrode material and its preparation method and application. The present disclosure first prepares a Prussian blue raw material solution at a low temperature, freezes a portion, and heats a portion to form nuclei to obtain a seed suspension. The seed suspension is then controlled to reflux over the surface of the frozen solution and enter a reactor. The inner layer of ice slowly melts to control the reaction rate. The reaction rate is controlled by the reaction between the slowly melting frozen solution and the nuclei, so that the reaction rate is low, particle agglomeration is reduced, and the electrical properties of the material are improved.

[0010] To achieve this purpose, the present disclosure adopts the following technical solutions:

[0011] In a first aspect, the present disclosure provides a method for preparing a Prussian blue positive electrode material, the preparation method comprising the following steps:

[0012] (1) freezing the first portion of the sodium ferrocyanide solution and the first portion of the transition metal salt solution, crushing the frozen sodium ferrocyanide solution and the transition metal salt solution at low temperature, mixing them, and pressing and freezing them to obtain a frozen mixed solution;

[0013] (2) mixing the second portion of the sodium ferrocyanide solution and the second portion of the transition metal salt solution at low temperature and then heating the mixture to obtain a seed crystal suspension;

[0014] (3) placing the frozen mixed solution in a reflux device, controlling the seed crystal suspension to reflux between the reactor and the reflux device, and performing aging treatment after the frozen mixed solution is completely dissolved to obtain the Prussian blue positive electrode material.

[0015] The present disclosure does not limit the order of operations of step (1) and step (2). Step (1) can be performed first, or step (2) can be performed first.

[0016] During the preparation process of the Prussian blue positive electrode material disclosed in the present invention, two parts of sodium ferrocyanide solution and transition metal salt solution are respectively subjected to freezing and low-temperature mixing-heating nucleation treatment. The present invention can suppress the growth process through low-temperature mixing-heating nucleation treatment, and can make the crystals grow slowly by controlling the melting rate of the frozen solution. The nucleation and growth occur in steps, and the crystals have high crystallinity, few defects, and less lattice water.

[0017] In one embodiment, the concentration of the sodium ferrocyanide solution in step (1) is 0.1 to 3 mol / L, for example, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L or 3 mol / L.

[0018] In one embodiment, the transition metal salt in the transition metal salt solution includes any one of iron salt, manganese salt, cobalt salt or nickel salt, or a combination of at least two thereof.

[0019] In one embodiment, the concentration of the transition metal salt solution is 0.1 to 3 mol / L, for example, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L or 3 mol / L.

[0020] In one embodiment, the temperature of the freezing treatment in step (1) is -30 to -50°C, for example: -30°C, -35°C, -40°C, -45°C or -50°C.

[0021] In one embodiment, the freezing treatment time is 5 to 12 hours, for example, 5 hours, 6 hours, 8 hours, 10 hours or 12 hours.

[0022] In one embodiment, the temperature of the low-temperature crushing treatment in step (1) is <-10°C.

[0023] In one embodiment, the particle size of the material obtained after the low temperature crushing is less than 2 mm.

[0024] In one embodiment, the pressing pressure is 0.1-10 MPa, for example, 0.1 MPa, 1 MPa, 2 MPa, 5 MPa or 10 MPa.

[0025] In one embodiment, the first portion of sodium ferrocyanide solution and the second portion of sodium ferrocyanide solution have the same concentration.

[0026] In one embodiment, the volume ratio of the first part of sodium ferrocyanide solution to the second part of sodium ferrocyanide solution is (6-9):(1-4), for example: 6:4, 7:3, 8:2, 8.5:1.5 or 9:1, etc.

[0027] In one embodiment, the first portion of the transition metal salt solution and the second portion of the transition metal salt solution have the same concentration.

[0028] In one embodiment, the volume ratio of the first portion of transition metal salt solution to the second portion of transition metal salt solution is (6-9):(1-4), for example: 6:4, 7:3, 8:2, 8.5:1.5 or 9:1, etc.

[0029] The first part of the sodium ferrocyanide solution and the second part of the sodium ferrocyanide solution disclosed herein can be prepared by dividing one sodium ferrocyanide solution into two parts, or the two parts of the sodium ferrocyanide solution can be prepared separately. The first part of the transition metal salt solution and the second part of the transition metal salt solution can be prepared by dividing one transition metal salt solution into two parts, or the two parts of the transition metal salt solution can be prepared separately.

[0030] In one embodiment, the temperature of the low-temperature mixing in step (2) is 3 to 20°C, for example, 3°C, 5°C, 10°C, 15°C or 20°C.

[0031] In one embodiment, the temperature of the heating treatment is 30-50°C, for example, 30°C, 35°C, 40°C, 45°C or 50°C.

[0032] In one embodiment, the temperature-elevating treatment time is 0.5 to 1 h, for example, 0.5 h, 0.6 h, 0.7 h, 0.8 h or 1 h.

[0033] In one embodiment, the reflux rate of the seed suspension in step (3) is 10 to 200 mL / min, for example, 10 mL / min, 50 mL / min, 100 mL / min, 150 mL / min or 200 mL / min.

[0034] In one embodiment, the temperature in the reactor is 30-60°C, for example, 30°C, 35°C, 40°C, 50°C or 60°C.

[0035] In one embodiment, the temperature of the aging treatment in step (3) is 50-90°C, for example, 50°C, 60°C, 70°C, 80°C or 90°C.

[0036] In one embodiment, the aging treatment time is 2 to 30 hours, for example, 2 hours, 5 hours, 10 hours, 15 hours or 30 hours.

[0037] In one embodiment, the aging atmosphere includes any one of nitrogen, argon or helium, or a combination of at least two of them.

[0038] In a second aspect, the present disclosure provides a Prussian blue positive electrode material, which is prepared by the method described in the first aspect.

[0039] In a third aspect, the present disclosure provides a positive electrode plate, which comprises the Prussian blue positive electrode material as described in the second aspect.

[0040] In a fourth aspect, the present disclosure provides a sodium ion battery, comprising the positive electrode sheet as described in the third aspect.

[0041] Compared with the prior art, the present disclosure has the following beneficial effects:

[0042] (1) The present invention first prepares a Prussian blue raw material solution at a low temperature, freezes a portion of it, and heats a portion of it to form nuclei to obtain a seed suspension. Then, the seed suspension is controlled to reflux over the surface of the frozen solution and enter the reactor. The outer layer of the reactor is controlled to grow at 30 to 60°C, and the inner layer of ice slowly melts to control the reaction rate. The reaction rate is controlled by the reaction between the slowly melted frozen solution and the crystal nuclei, so that the reaction rate is low, the agglomeration of particles is reduced, and the electrical properties of the material are better.

[0043] (2) The freezing process described in the present disclosure can evenly disperse ions in the solution, preventing a sudden increase in local ion concentration and preventing their free movement. Instead, as the ice melts, it reacts with the surrounding crystal nuclei, resulting in a more uniform and sufficient reaction. The reflux device used can better enable the particles to melt and crystallize slowly and avoid agglomeration.

[0044] (3) The sodium ion battery made of the Prussian blue positive electrode material prepared by the method disclosed in the present invention has an initial discharge capacity of more than 140.67 mAh / g at 0.1C, and a discharge capacity of more than 131.04 mAh / g after 100 cycles.

[0045] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0047] FIG1 is a schematic diagram of an apparatus used in a method for preparing a Prussian blue cathode material according to an embodiment of the present disclosure, comprising: 1-frozen mixed solution; 2-reflux device; 3-pump; 4-reactor; 5-stirring rod; and 6-seed suspension.

[0048] FIG2 is a SEM image of the Prussian blue positive electrode material prepared in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0049] The technical solution of the present disclosure is further described below through specific implementation methods. It should be understood by those skilled in the art that the embodiments are only used to help understand the present disclosure and should not be regarded as specific limitations of the present disclosure.

[0050] Example 1

[0051] This embodiment provides a Prussian blue positive electrode material. The schematic diagram of the device used in the preparation method of the Prussian blue positive electrode material is shown in Figure 1, wherein 1 is a frozen mixed solution, 2 is a reflux device, 3 is a pump, 4 is a reactor, 5 is a stirring rod, and 6 is a seed crystal suspension. The preparation method is as follows:

[0052] (1) 1.5 mol of sodium ferrocyanide was dissolved in 1 L of deionized water to obtain a sodium ferrocyanide solution, and 1.5 mol of ferrous chloride was dissolved in 1 L of deionized water to obtain a ferrous chloride solution. 800 mL of the sodium ferrocyanide solution and 800 mL of the ferrous chloride solution were frozen at -40°C for 8 h, respectively. The frozen sodium ferrocyanide solution and ferrous chloride solution were crushed at -20°C to obtain a smooth-like sodium ferrocyanide solution and a smooth-like ferrous chloride solution. The smooth-like sodium ferrocyanide solution and the smooth-like ferrous chloride solution were then mixed evenly and pressed into a circular mold at a pressure of 1 MPa. The mixture was then frozen at -40°C for 8 h to obtain a frozen mixed solution that was frozen into balls.

[0053] (2) mixing the remaining sodium ferrocyanide solution and ferrous chloride solution at 10°C, then heating to 40°C and reacting for 0.7h to obtain a seed crystal suspension;

[0054] (3) The seed suspension was added to the reactor, and the frozen mixed solution was then placed in a reflux device with a reflux flow rate of 100 mL / min. The temperature was increased and the temperature within the 3 cm liquid thickness of the reactor wall was controlled to be 50°C. After the reaction was completed until the frozen mixed solution was completely melted, the mixed solution was heated to 60°C as a whole, and argon was introduced as a protective atmosphere. The mixture was kept warm and aged for 12 hours to obtain a suspension. The suspension was separated by solid-liquid separation, and the precipitate was washed with deionized water 3 times. The precipitate was then dried under a vacuum of 100 Pa and a temperature of 80°C for 12 hours to obtain a Prussian blue positive electrode material.

[0055] The SEM image of the Prussian blue-based cathode material is shown in FIG2 .

[0056] Example 2

[0057] This embodiment provides a Prussian blue positive electrode material, and the preparation method of the Prussian blue positive electrode material is as follows:

[0058] (1) 0.1 mol of sodium ferrocyanide was dissolved in 1 L of deionized water to obtain a sodium ferrocyanide solution, 0.1 mol of ferrous chloride was dissolved in 1 L of deionized water to obtain a ferrous chloride solution, 600 mL of the sodium ferrocyanide solution and 600 mL of the ferrous chloride solution were frozen at -30°C for 12 h, the frozen sodium ferrocyanide solution and the ferrous chloride solution were crushed at -15°C to obtain a smoothie-like sodium ferrocyanide solution and a ferrous chloride solution, and then the smoothie-like sodium ferrocyanide solution and the ferrous chloride solution were mixed evenly and pressed into a circular mold at a pressure of 0.1 MPa, and then frozen at -30°C for 12 h to obtain a frozen mixed solution that was frozen into balls;

[0059] (2) mixing the remaining sodium ferrocyanide solution and ferrous chloride solution at 3°C, then heating to 30°C and reacting for 1 hour to obtain a seed crystal suspension;

[0060] (3) The seed suspension was added to the reactor, and the frozen mixed solution was then placed in a reflux device with a reflux flow rate of 10 mL / min. The temperature was increased and the temperature within the 3 cm liquid thickness of the reactor wall was controlled to be 30°C. After the reaction was completed until the frozen mixed solution was completely melted, the mixed solution was heated to 50°C as a whole, and argon was introduced as a protective atmosphere. The mixture was kept warm and aged for 30 hours to obtain a suspension. The suspension was separated into solid and liquid, and the precipitate was washed with deionized water 3 times. The precipitate was then dried under a vacuum of 100 Pa and a temperature of 80°C for 12 hours to obtain a Prussian blue positive electrode material.

[0061] Example 3

[0062] This embodiment provides a Prussian blue positive electrode material, and the preparation method of the Prussian blue positive electrode material is as follows:

[0063] (1) 3 mol of sodium ferrocyanide was dissolved in 1 L of deionized water to obtain a sodium ferrocyanide solution, and 3 mol of ferrous chloride was dissolved in 1 L of deionized water to obtain a ferrous chloride solution. 900 mL of the sodium ferrocyanide solution and 900 mL of the ferrous chloride solution were frozen at -50°C for 5 h, respectively. The frozen sodium ferrocyanide solution and ferrous chloride solution were crushed at -18°C to obtain a smoothie-like sodium ferrocyanide solution and a smoothie-like ferrous chloride solution. The smoothie-like sodium ferrocyanide solution and the smoothie-like ferrous chloride solution were then mixed evenly and pressed into a circular mold at a pressure of 10 MPa. The mixture was then frozen at -50°C for 5 h to obtain a frozen mixed solution that was frozen into balls.

[0064] (2) mixing the remaining sodium ferrocyanide solution and ferrous chloride solution at 20°C, then heating to 50°C and reacting for 0.5h to obtain a seed crystal suspension;

[0065] (3) The seed suspension was added to the reactor, and the frozen mixed solution was then placed in a reflux device with a reflux flow rate of 200 mL / min. The temperature was increased and the temperature within the 3 cm liquid thickness of the reactor wall was controlled to be 60°C. After the reaction was completed until the frozen mixed solution was completely melted, the mixed solution was heated to 90°C as a whole, and argon was introduced as a protective atmosphere. The mixture was kept warm and aged for 2 hours to obtain a suspension. The suspension was separated into solid and liquid, and the precipitate was washed with deionized water 3 times. The precipitate was then dried under a vacuum of 100 Pa and a temperature of 80°C for 12 hours to obtain a Prussian blue positive electrode material.

[0066] Example 4

[0067] The only difference between this embodiment and embodiment 1 is that the temperature of the heating in step (2) is 20° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0068] Example 5

[0069] The only difference between this embodiment and embodiment 1 is that the temperature of the heating in step (2) is 60° C., and the other conditions and parameters are exactly the same as those in embodiment 1.

[0070] Example 6

[0071] The only difference between this embodiment and embodiment 1 is that the temperature in the reactor is 20° C., and other conditions and parameters are exactly the same as those in embodiment 1.

[0072] Example 7

[0073] The only difference between this embodiment and embodiment 1 is that the temperature in the reactor is 70° C., and other conditions and parameters are exactly the same as those in embodiment 1.

[0074] Comparative Example 1

[0075] This comparative example provides a Prussian blue positive electrode material, and the preparation method of the Prussian blue positive electrode material is as follows:

[0076] (1) 1.5 mol of sodium ferrocyanide was dissolved in 1 L of deionized water to obtain solution A, and 1.5 mol of ferrous chloride was dissolved in 1 L of deionized water to obtain solution B. Solution A and solution B were mixed at 10°C, then heated to 40°C, and reacted for 0.7 h to obtain seed solution D. The temperature was then increased to control the temperature at 60°C, argon gas was introduced as a protective atmosphere, and the mixture was kept warm and aged for 12 h to obtain a suspension.

[0077] (2) The suspension was separated, and the precipitate was washed three times with deionized water. The precipitate was then dried under a vacuum of 100 Pa and a temperature of 80° C. for 12 h to obtain a Prussian blue-based positive electrode material.

[0078] Comparative Example 2

[0079] This comparative example provides a Prussian blue positive electrode material, and the preparation method of the Prussian blue positive electrode material is as follows:

[0080] (1) 1.5 mol of sodium ferrocyanide was dissolved in 1 L of deionized water to obtain solution A, and 1.5 mol of ferrous chloride was dissolved in 1 L of deionized water to obtain solution B. Solution A and solution B were mixed, and then the temperature was raised to 60° C., argon gas was introduced as a protective atmosphere, and the suspension was kept warm for 12 h to obtain a suspension.

[0081] (2) The suspension was separated, and the precipitate was washed three times with deionized water. The precipitate was then dried under a vacuum of 100 Pa and a temperature of 80° C. for 12 h to obtain a Prussian blue-based positive electrode material.

[0082] Performance testing:

[0083] The Prussian blue cathode materials prepared in the examples and comparative examples were assembled into organic electrolyte system sodium ion half-cells, and electrochemical performance tests were performed. The test results are shown in Table 1:

[0084] Table 1

[0085] As can be seen from Table 1, it can be obtained from Examples 1-3 that the 0.1C first discharge specific capacity of the sodium ion battery prepared by the method of the present disclosure using the Prussian blue positive electrode material can reach more than 140.67 mAh / g, and the discharge specific capacity after 100 cycles can reach more than 131.04 mAh / g. A high reactant concentration will make the reaction rate faster, and the positive electrode material particles formed will be larger. A low reactant concentration will make the reaction rate slow, and the generated grains will be too fine, but the reactant concentration within a reasonable range has little effect on the material properties.

[0086] By comparing Example 1 with Examples 4-5, it can be seen that in the preparation process of the Prussian blue-based positive electrode material described in the present disclosure, the preparation heating temperature of the seed suspension will affect its performance. When the heating temperature is controlled at 30-50°C, the performance of the Prussian blue-based positive electrode material obtained is better. If the heating temperature is too low, it is difficult for the reactants to form a suitable crystal form, thereby affecting the material performance. If the heating temperature is too high, the crystallization rate will become too fast, resulting in a large number of crystal defects in the formed crystals, affecting the electrochemical properties of the material.

[0087] By comparing Example 1 with Examples 6-7, it can be seen that during the preparation process of the Prussian blue-based positive electrode material described in the present disclosure, the temperature of the reactor will affect its performance. When the temperature of the reactor is controlled at 30-60°C, the performance of the Prussian blue-based positive electrode material obtained is better. If the temperature of the reactor is too low, the reactants are difficult to grow into the expected crystal form, the material crystallinity is poor, and the performance of the positive electrode material is reduced. If the temperature of the reactor is too high, the material grows too fast, and a large number of defects will be generated during the crystallization process, affecting the electrochemical properties of the material.

[0088] From the comparison between Example 1 and Comparative Example 1, it can be seen that the freezing treatment disclosed in the present invention can evenly disperse the ions in the solution, does not cause a sudden increase in local ion concentration, and can prevent their free movement. Instead, as the ice melts and reacts with the surrounding crystal nuclei, the reaction is more uniform and sufficient.

[0089] As can be seen from the comparison between Example 1 and Comparative Example 2, the present disclosure first prepares a Prussian blue raw material solution at a low temperature, freezes a portion, and heats a portion to form nuclei to obtain a seed suspension. The seed suspension is then controlled to reflux over the surface of the frozen solution and enter the reactor. The outer layer of the reactor is controlled to grow at 30-60°C, and the inner layer of ice slowly melts to control the reaction rate. The reaction rate is controlled by the reaction between the slowly melting frozen solution and the crystal nuclei, resulting in a low reaction rate, reduced particle agglomeration, and better electrical properties of the material.

Claims

1. A method for preparing a Prussian blue positive electrode material, the preparation method comprising the following steps: (1) freezing the first part of the sodium ferrocyanide solution and the first part of the transition metal salt solution, crushing the frozen sodium ferrocyanide solution and the transition metal salt solution at low temperature, mixing them, and pressing and freezing them to obtain a frozen mixed solution; (2) mixing the second part of the sodium ferrocyanide solution and the second part of the transition metal salt solution at low temperature and then heating the mixture to obtain a seed crystal suspension; (3) placing the frozen mixed solution in a reflux device, controlling the seed crystal suspension to reflux between the reaction kettle and the reflux device, and performing an aging treatment after the frozen mixed solution is completely dissolved to obtain the Prussian blue positive electrode material.

2. The preparation method according to claim 1, wherein The concentration of the sodium ferrocyanide solution in step (1) is 0.1-3 mol / L.

3. The preparation method according to claim 1 or 2, wherein: The transition metal salt in the transition metal salt solution includes any one of iron salt, manganese salt, cobalt salt or nickel salt, or a combination of at least two of them.

4. The preparation method according to any one of claims 1 to 3, wherein The concentration of the transition metal salt solution is 0.1-3 mol / L.

5. The preparation method according to any one of claims 1 to 4, wherein: The temperature of the freezing treatment in step (1) is -30 to -50°C.

6. The preparation method according to any one of claims 1 to 5, wherein: The freezing treatment time is 5 to 12 hours.

7. The preparation method according to any one of claims 1 to 6, wherein: The temperature of the low temperature crushing treatment is <-10°C.

8. The preparation method according to any one of claims 1 to 7, wherein: The particle size of the material obtained after the low temperature crushing is less than 2mm.

9. The preparation method according to any one of claims 1 to 8, wherein: The pressing pressure is 0.1-10 MPa.

10. The preparation method according to any one of claims 1 to 9, wherein: The concentrations of the first part of sodium ferrocyanide solution and the second part of sodium ferrocyanide solution are the same.

11. The preparation method according to any one of claims 1 to 10, wherein: The volume ratio of the first part of sodium ferrocyanide solution to the second part of sodium ferrocyanide solution is (6-9):(1-4).

12. The preparation method according to any one of claims 1 to 11, wherein: The concentrations of the first portion of transition metal salt solution and the second portion of transition metal salt solution are the same.

13. The preparation method according to any one of claims 1 to 12, wherein: The volume ratio of the first part of transition metal salt solution to the second part of transition metal salt solution is (6-9):(1-4).

14. The preparation method according to any one of claims 1 to 13, wherein: The temperature of the low-temperature mixing in step (2) is 3 to 20° C.; Optionally, the temperature of the heating treatment is 30-50°C; Optionally, the temperature rising treatment time is 0.5 to 1 hour.

15. The preparation method according to any one of claims 1 to 14, wherein: The reflux rate of the seed suspension in step (3) is 10 to 200 mL / min; Optionally, the temperature in the reactor is 30-60°C.

16. The preparation method according to any one of claims 1 to 15, wherein: The temperature of the aging treatment in step (3) is 50 to 90° C. Optionally, the aging treatment time is 2 to 30 hours; Optionally, the aging treatment atmosphere includes any one of nitrogen, argon or helium, or a combination of at least two of them.

17. A Prussian blue positive electrode material, wherein the Prussian blue positive electrode material is prepared by the method according to any one of claims 1 to 16.

18. A positive electrode plate, comprising the Prussian blue positive electrode material according to claim 17.

19. A sodium ion battery, comprising the positive electrode sheet according to claim 18.

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