Preparation method of Prussian blue positive electrode material and positive electrode material thereof

Abstract

The invention relates to the technical field of positive electrode materials for energy storage of sodium-ion batteries, in particular to a preparation method of a Prussian blue positive electrode material and the positive electrode material thereof. The method is obtained based on the existing overflow method synthesis improvement, in the crystal forming process, the crystal nucleus forming step and the growth step are separated, the pH value of a mixed solution is adjusted in the two steps respectively, and meanwhile, a plurality of growth kettles are arranged to synchronously receive the mixed solution generated in a granulation kettle. On one hand, formation of crystal nucleuses can be facilitated and is matched with the feeding speed of raw materials, the situation that the raw materials are continuously supplied but not used for formation of the crystal nucleuses and are used for growth of generated crystal nucleuses is avoided, and it is guaranteed that the particle sizes of the crystal nucleuses in the growth stage are uniform, and the generation amount of the crystal nucleuses can meet the crystal growth requirement; meanwhile, the crystal can grow slowly, crystal defects are reduced, the Prussian blue type positive electrode material with better performance can be obtained, and it is ensured that the percent of pass of the Prussian blue type positive electrode material is increased.

Description

Technical Field

[0001] The invention relates to the technical field of positive electrode materials for sodium ion battery energy storage, and in particular to a preparation method of a Prussian blue positive electrode material and the positive electrode material. Background Art

[0002] The chemical formula of Prussian blue and its analogs (PBAs) can be expressed as A x M1[M2(CN)6]·nH2O (0≤x≤2), where A is an alkali metal ion (such as Na+, K+, etc.), M1 and M2 are transition metal ions with different coordination (such as Mn, Fe, Co, Ni, Cu, Zn, Cr, etc.), and nH2O is crystal water.

[0003] Prussian blue has a face-centered cubic structure. The metal M and ferrocyanide in the lattice are arranged according to Fe-C≡NM to form a three-dimensional skeleton structure. The Fe ions and M ions are arranged in a cube at the vertices, C≡N is located on the edges of the cube, and the embedded ions A + The lattice H2O molecules are in the cubic gaps. This unique three-dimensional open framework structure allows ions (such as Na+) to diffuse and embed / extract quickly in the material, thereby providing high ionic conductivity and fast charge and discharge performance. At the same time, Prussian blue material also has good chemical stability and environmental friendliness, as well as relatively low cost, so it has quickly become a research hotspot in the field of battery materials.

[0004] There are many methods for preparing Prussian blue cathode materials. In the invention "Prussian blue cathode material and continuous preparation method thereof and sodium ion battery" with authorization announcement number CN 115072741, sodium ferrocyanide solution, ammonia solution, acid solution and mixed solution A are added to the bottom liquid of the reactor in parallel to carry out a continuous coprecipitation reaction. During the reaction, the pH value of the reaction system is controlled to be 4-9, and the residence time of the reaction materials in the reactor does not exceed 20 hours; after the continuous coprecipitation reaction is stable, the reactor continuously overflows slurry, the overflowed slurry is subjected to solid-liquid separation, and the solid phase is aged, washed and dried to obtain the Prussian blue cathode material.

[0005] In the above-mentioned steps of synthesis by overflow method, only one reactor is used for the formation and growth of crystals. In the process of crystal formation, it is usually necessary to first granulate to obtain crystal nuclei, and then rely on the crystal nuclei to grow the crystals. In the granulation step of Prussian blue materials, when the pH value of the mixed solution is neutral or alkaline, it is conducive to the generation of crystal nuclei; and in the growth step of Prussian blue materials, when the pH value of the mixed solution is neutral or acidic, it is conducive to the growth of crystals. Therefore, the adjustment range of pH value in a single reactor is limited. And when the pH value is adjusted, it will affect both the crystal nucleus formation and the crystal growth process, and the conditions required for crystal nucleus formation and crystal growth conflict. Therefore, if the pH value is not adjusted properly, it is easy to cause large fluctuations, which ultimately leads to defects in the finished crystals and poor consistency of the crystals obtained during continuous production. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a Prussian blue positive electrode material, which is improved based on the existing overflow synthesis method. On the one hand, it can help the formation of crystal nuclei and match the feeding speed of raw materials, avoiding the situation that the raw materials are continuously supplied but not used for crystal nuclei formation but used for the growth of generated crystal nuclei, and ensures that the particle size of the crystal nuclei entering the growth stage is relatively uniform and the amount of crystal nuclei generated can meet the crystal growth requirements; at the same time, the present invention ensures that the crystals can grow slowly, reduces the generation of crystal defects, is conducive to obtaining Prussian blue positive electrode materials with better performance, and ensures that the qualified rate of Prussian blue positive electrode materials is improved.

[0007] The present invention is achieved through the following technical solutions.

[0008] A method for preparing a Prussian blue positive electrode material, characterized in that it comprises the following steps: S1. Prepare sodium ferrocyanide solution, transition metal source solution with iron-manganese molar ratio Fe:Mn=1:0~3, and precipitant solution, which are respectively recorded as A solution, B solution, and C solution; wherein the transition metal source solution is used to provide transition metals such as iron and manganese required for preparing Prussian blue positive electrode materials.

[0009] S2. Add water, a complexing agent and a sodium supplement to a granulation kettle and heat and stir to obtain an initial mixed solution; add liquid A, liquid B and liquid C to the initial mixed solution and stir to obtain a first mixed solution, and control the amount of liquid C added so that the pH value of the first mixed solution is 6-10; detect the particle size of the first mixed solution at the discharge port of the granulation kettle.

[0010] The feed port in the granulation kettle and other kettles is placed at the bottom and the discharge port is placed at the top. Therefore, in the process of continuously feeding into the granulation kettle, the first mixed liquid at the top will overflow into the growth kettle through the discharge port. In the granulation kettle, under this reaction environment, it is conducive to the generation of crystal nuclei, but not conducive to the further growth of crystal nuclei. Therefore, when the raw materials are continuously input, it is ensured that the raw materials are used to generate crystal nuclei instead of growing the already formed crystal nuclei. On the one hand, it ensures the large-scale generation of crystal nuclei, and on the other hand, it makes the particle size of the crystal nuclei produced in the granulation kettle more uniform.

[0011] S3. When the particle size in the first mixed liquid reaches 0.5~3μm, n groups of growth kettles receive the first mixed liquid overflowing from the granulation kettle, wherein n is an integer ≥2; liquid A, liquid B and liquid C are added to several of the growth kettles and stirred to obtain a second mixed liquid, and the amount of liquid C added is controlled to make the pH value of the second mixed liquid 4~7, which is more conducive to the growth of crystals; the particle size of the second mixed liquid is detected at the discharge port of the growth kettle.

[0012] Several groups of growth kettles are set up to simultaneously receive the first mixed liquid produced in the granulation kettle. On the one hand, this can make the receiving rate of the crystal growth link compatible with the production rate of the granulation link, thereby ensuring the smooth progress of the production steps; on the other hand, under the premise of rate adaptation, after several growth kettles are set up, each growth kettle receives less first mixed liquid provided by the granulation kettle, and accordingly, the feed amount of liquid A and liquid B in each growth kettle can be reduced. If n groups of growth kettles are set up, the feed amount of liquid A and liquid B in each growth kettle can be reduced to about 1 / n±1 / 8 of the feed amount of liquid A and liquid B in S2, which prolongs the residence time of the crystal, reduces the growth rate of the crystal, is more conducive to crystal formation, and makes the final crystal have fewer defects.

[0013] S4. When the particle size in the second mixed liquid reaches 6-20 μm, the aging kettle receives the second mixed liquid overflowing from the growth kettle.

[0014] S5. Centrifuge, wash and dry the third mixed solution overflowing from the aging kettle after aging to obtain a Prussian blue positive electrode material.

[0015] As a further improvement of the present invention, the total sodium concentration in the initial mixed solution in S2 is 1-6 mol / L, which ensures that the molar amount of sodium element is sufficient during the granulation process and that the material performance meets the standards.

[0016] As a further improvement of the present invention, in S2-S3, the ratio of the amount of liquid A to liquid B is controlled so that the ratio of the solute molar amount of liquid A to the solute molar amount of liquid B is 1:0.5-3; the amount of complexing agent added is controlled so that the concentration of the complexing agent in the first mixed solution is 2-3 mol / L, and the concentration of the complexing agent in the second mixed solution is 0.5-2 mol / L. In the granulation process, controlling a higher complexing agent concentration is conducive to particle dispersion; and in the growth process, controlling a lower complexing agent concentration is conducive to improving particle growth and improving material properties.

[0017] As a further improvement of the present invention, the complexing agent is any one or more of complexing agents such as sodium citrate, ammonia water, ethylenediamine, EDTA, etc.; the precipitating agent is any one or more of strong bases such as sodium hydroxide and potassium hydroxide; the sodium supplementer is any one or more of sodium salts such as sodium sulfate, sodium chloride, sodium carbonate, sodium bicarbonate, etc.

[0018] As a further improvement of the present invention, the solute concentration of the A solution is 0.1-0.5 mol / L, the solute concentration of the B solution is 0.5-3 mol / L, and the solute concentration of the C solution is 2-20 mol / L.

[0019] As a further improvement of the present invention, the reaction temperature in the granulation kettle described in S2 is 20~70°C, the reaction temperature in the growth kettle described in S3 is 20~50°C; and in the aging kettle described in S4, the reaction temperature during the aging process is 50~80°C.

[0020] As a further improvement of the present invention, the stirring speed of the granulation kettle described in S2 is 200~700 rpm; the stirring speed of the growth kettle described in S3 is 200~600 rpm; in the aging kettle described in S4, the stirring speed during the aging process is 100~400 rpm.

[0021] As a further improvement of the present invention, S3~S4 respectively include the following empty kettle start-up steps for the growth kettle and the aging kettle: before the growth kettle receives the first mixed liquid overflowing from the granulation kettle, and before the aging kettle receives the second mixed liquid overflowing from the growth kettle, water is added to the growth kettle and the aging kettle respectively, so that the stirring devices in the growth kettle and the aging kettle are both placed in water.

[0022] As a further improvement of the present invention, after the particle size of the first mixed liquid meets the standard, the residence time of the first mixed liquid in the granulation kettle is 0.5~10 h; after the particle size of the second mixed liquid meets the standard, the residence time of the second mixed liquid in the growth kettle is 4~24 h; and the aging time in the aging kettle is 2~12 h.

[0023] A Prussian blue positive electrode material, characterized in that it is prepared by using the above-mentioned method for preparing a Prussian blue positive electrode material.

[0024] The beneficial effects of the present invention include: (1) The granulation stage and the growth stage, which require different reaction conditions, are separated, ensuring that the raw materials input into the granulation kettle can be fully used for the generation of crystal nuclei rather than the growth of crystal nuclei, ensuring the high consistency of the particle size of the first mixed liquid when the granulation kettle is discharged, and thus making the crystals more consistent after the crystal nuclei grow in the growth kettle, reducing the occurrence of some crystals growing well while others growing poorly, and improving the qualified rate of crystals; (2) Multiple growth reactors simultaneously receive the first mixed liquid from the granulation reactor, so that the growth stage of the crystal can be adapted to the generation speed of the crystal nucleus in the granulation stage. Under this premise, the residence time of the crystal in the growth reactor is extended, ensuring the long-term and steady growth of the crystal, reducing the defects of the crystal, and improving the performance of the crystal; (3) The overall production system can be started once to ensure continuous production. In theory, there is no need for a second start-up. During the overall production process, the reaction utilization rate is greatly improved. In addition, since the production links of the granulation reactor and the growth reactor with different required reaction conditions are separated, the difficulty of controlling the parameters of related material addition during the production process is reduced, making it easier to make timely adjustments. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below based on implementation cases.

[0026] In order to make the purpose, technical scheme and advantages of the present invention more clear, the present invention is further described in detail in combination with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] In the embodiment of the present invention, the complexing agent used is sodium citrate, the precipitating agent is sodium chloride, and the sodium supplementing agent is ammonium carbonate. The feed inlets of the granulation kettle, the growth kettle, and the aging kettle used in this embodiment are all arranged at the bottom of the kettle, and the discharge port is arranged near the top of the kettle. Therefore, in this embodiment, the residence time = feed flow rate / total volume from the feed inlet to the discharge port.

[0028] Embodiment 1: A method for preparing a Prussian blue positive electrode material comprises the following steps: S1. Prepare a sodium ferrocyanide solution with a solute concentration of 0.1 mol / L, a mixed solution of ferric sulfate and manganese sulfate with a solute concentration of 0.5 mol / L as a transition metal source solution, wherein the iron-manganese molar ratio Fe:Mn=1:1, and a precipitant solution with a solute concentration of 2 mol / L, and record them as A solution, B solution, and C solution respectively.

[0029] S2. Add 300L of water, 28kg of complexing agent and 3kg of sodium supplement to a granulation kettle with a volume of 1000L to form an initial mixed solution, and the total sodium concentration in the initial mixed solution is 1 mol / L. Turn on the stirring device in the granulation kettle and set the stirring speed to 700 rpm; heat the initial mixed solution to a temperature of 70 ℃. Then add liquid A, liquid B and liquid C to form a first mixed solution. The ratio of the solute molar amount of liquid A to the solute molar amount of liquid B is 1:0.5; at the same time, the pH value of the first mixed solution is detected by an online pH value detection device to ensure that the pH value of the first mixed solution is controlled at about 7.5 after adding liquid C; the residence time of the first mixed solution in the granulation kettle is 1 h. Continue to add complexing agent to control the concentration of complexing agent in the first mixed solution to 2 mol / L. The particle size of the first mixed liquid is detected at the discharge port of the granulation kettle, and the pH value is adjusted according to the particle size result. If the particle size test value is larger than the stable value, the pH value is increased; if the particle size test value is smaller than the stable value, the pH value is decreased.

[0030] S3. In this embodiment, four groups of growth kettles are provided to simultaneously receive the first mixed liquid from the granulation kettle. Before receiving the first mixed liquid, the growth kettle is started with an empty kettle, and 300 L of water is added to the growth kettle with a volume of 1000 L so that the water can cover the stirring device in the kettle, and then the stirring device is turned on and the stirring speed is set to 200 rpm; at the same time, the water is heated to a temperature of 50 °C. When the particle size of the first mixed liquid detected at the discharge port in the granulation kettle reaches 2.5 μm, the four groups of growth kettles begin to receive the first mixed liquid from the granulation kettle. When the liquid level in the growth kettle stabilizes and begins to overflow from the discharge port, liquid A, liquid B and liquid C are added to the growth kettle to form a second mixed liquid. The ratio of the molar amount of the solute in liquid A to the molar amount of the solute in liquid B is 1:0.5, but in each growth kettle, the feed flow rate of liquid A and liquid B is 1 / 4 of that in S2, so that the residence time of the second mixed liquid in the growth kettle is 20 h; at the same time, the pH value of the second mixed liquid is detected by an online pH value detection device to ensure that the pH value of the second mixed liquid is controlled at about 6.5 after adding liquid C. Continue to add the complexing agent to control the concentration of the complexing agent in the second mixed liquid to 1 mol / L. Detect the particle size of the second mixed liquid at the discharge port of the granulation kettle, and adjust the pH value according to the particle size result. If the particle size test value is larger than the stable value, adjust the pH value upward, and if the particle size test value is smaller than the stable value, adjust the pH downward.

[0031] S4. Before receiving the second mixed liquid, the aging kettle is started with an empty kettle, and 300 L of water is added to the aging kettle with a volume of 1000 L, so that the water can cover the stirring device in the kettle, and then the stirring device is turned on, and the stirring speed is set to 100 rpm; at the same time, the water is heated to a temperature of 80 ° C. When the particle size of the second mixed liquid detected at the discharge port in the growth kettle reaches 15 μm, the aging kettle begins to receive the second mixed liquid from the growth kettle and age it. The specific aging step is a mature existing technology, so it will not be repeated in this embodiment. In this embodiment, the temperature in the aging kettle is controlled to 60 ° C, and the aging time is 8 h.

[0032] S5. Continuously input liquid A, liquid B, liquid C, complexing agent and other raw materials into the granulation kettle and the growth kettle, so that each kettle can operate continuously and stably. The growth kettle continuously receives the first mixed liquid output from the discharge port of the granulation kettle, and the aging kettle continuously receives the second mixed liquid output from the discharge port of the growth kettle.

[0033] S6. The aged third mixed solution overflowing from the aging kettle is centrifuged, washed, and dried to obtain a Prussian blue positive electrode material, wherein the centrifugation, washing, and drying steps are mature existing technologies and will not be repeated in this embodiment.

[0034] Embodiment 2: The difference between this embodiment and embodiment 1 is that: In S2 of this embodiment, the total sodium concentration in the initial mixed solution is 1 mol / L, the pH value of the first mixed solution is controlled at about 7.5, the concentration of the complexing agent in the first mixed solution is 3 mol / L, the residence time of the first mixed solution in the granulation kettle is 5 h, and the particle size of the first mixed solution detected at the discharge port of the granulation kettle is 1 μm; In S3 of this embodiment, the pH value of the second mixed solution is controlled at about 6.5, the concentration of the complexing agent in the second mixed solution is 2 mol / L, the residence time of the second mixed solution in the growth kettle is 5 h, and the particle size of the second mixed solution detected at the outlet of the growth kettle is 8 μm; In S4 of this embodiment, the temperature in the aging kettle is controlled to be 50° C. and the aging time is 6 h.

[0035] Embodiment 3: The difference between this embodiment and embodiment 1 is that: In S2 of this embodiment, the total sodium concentration in the initial mixed solution is 1 mol / L, the pH value of the first mixed solution is controlled at about 9, the complexing agent concentration in the first mixed solution is 2.5 mol / L, the residence time of the first mixed solution in the granulation kettle is 0.5 h, and the particle size of the first mixed solution detected at the discharge port of the granulation kettle is 3 μm; In S3 of this embodiment, the pH value of the second mixed solution is controlled at about 6, the concentration of the complexing agent in the second mixed solution is 1 mol / L, the residence time of the second mixed solution in the growth kettle is 10 h, and the particle size of the second mixed solution detected at the outlet of the growth kettle is 18 μm; In S4 of this embodiment, the temperature in the aging kettle is controlled to be 80° C. and the aging time is 3 h.

[0036] Embodiment 4: A Prussian blue positive electrode material prepared by the preparation method of Example 1 has a product qualification rate of 95%. The relevant testing requirements for the qualification rate are as follows: The production requirements for Prussian blue positive electrode materials are: in batteries prepared using Prussian blue positive electrode materials, the 0.1C charge discharge capacity is greater than 150 mAh / g, and the first efficiency is greater than 95%.

[0037] The button battery manufacturing process includes the following steps: (1) Mix the positive electrode material: carbon nanotube (CNT): PVDF (Solvay 5130) in a ratio of 90:5:5, and add N-methylpyrrolidone (NMP) to mix and slurry; (2) The slurry is coated and dried to obtain a pole piece surface with a pole piece surface density of 8 mg / cm 3 After rolling with a small roller press, the pole piece density is compacted to 1.2g / cm 3 , cut the pole piece into a circular pole piece with a diameter of 14 mm for later use; (3) In this embodiment, a sodium sheet is used as the counter electrode of the battery, sodium perchlorate electrolyte is selected, and a ceramic diaphragm of Xingyuan is selected. The diaphragm is cut into discs with a diameter of 16 mm and assembled into a CR2032 button battery in the order of positive electrode shell, positive electrode sheet, diaphragm, negative electrode sheet, gasket, spring and negative electrode shell.

[0038] The button cell was tested accordingly, the testing voltage was 2.0-4.0V, and the testing equipment was LAND. In this embodiment, 20 batches of Prussian blue positive electrode materials produced continuously were selected by the preparation method in Example 1, and the button cell production and testing methods were used for testing. The product qualification rate = qualified batch / total batch*100%, and the product qualification rate of the Prussian blue positive electrode material was 95%, which was relatively high.

[0039] Finally, it should be noted that the above implementation cases are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned implementation cases, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned implementation cases, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the implementation cases of the present invention.

Claims

1. A method for preparing a Prussian blue cathode material, characterized in that: The following steps are involved: S1. Prepare sodium ferrocyanide solution, transition metal source solution with iron-manganese molar ratio Fe:Mn=1:0~3, and precipitant solution, which are respectively recorded as A solution, B solution, and C solution; S2. Add water, complexing agent and sodium supplement to the granulation kettle and heat and stir to obtain an initial mixed solution; Adding liquid A, liquid B and liquid C to the initial mixed solution and stirring to obtain a first mixed solution, and controlling the amount of liquid C added so that the pH value of the first mixed solution is 6-10; detecting the particle size of the first mixed liquid at the discharge port of the granulation kettle; S3. When the particle size in the first mixed solution reaches 0.5 to 3 μm, n groups of growth reactors receive the first mixed solution overflowing from the granulation reactor, wherein n is an integer ≥ 2; Adding liquid A, liquid B and liquid C into a plurality of the growth kettles and stirring to obtain a second mixed liquid, and controlling the amount of liquid C added so that the pH value of the second mixed liquid is 4-7; detecting the particle size of the second mixed liquid at the discharge port of the growth kettle; S4. When the particle size of the second mixed solution reaches 6 to 20 μm, the aging reactor receives the second mixed solution overflowing from the growth reactor; S5. continuously inputting raw materials into the granulation kettle and the growth kettle, the growth kettle continuously receives the first mixed solution output from the discharge port of the granulation kettle, and the aging kettle continuously receives the second mixed solution output from the discharge port of the growth kettle; S6. Centrifuge, wash and dry the aged third mixed solution overflowing from the aging kettle to obtain a Prussian blue positive electrode material.

2. The method for preparing a Prussian blue positive electrode material according to claim 1, characterized in that: The total sodium concentration in the initial mixed solution in S2 is 1~6 mol / L.

3. The method for preparing a Prussian blue positive electrode material according to claim 1, characterized in that: In S2~S3, the ratio of the added amount of liquid A to that of liquid B is controlled so that the ratio of the solute molar amount of liquid A to the solute molar amount of liquid B is 1:0.5~3; the amount of complexing agent added is controlled so that the concentration of the complexing agent in the first mixed solution is 2~3 mol / L, and the concentration of the complexing agent in the second mixed solution is 0.5~2 mol / L.

4. The method for preparing a Prussian blue positive electrode material according to claim 1, characterized in that: The complexing agent is any one or more of sodium citrate, ammonia water, ethylenediamine, and EDTA; the precipitating agent is any one or more of sodium hydroxide and potassium hydroxide; and the sodium supplement is any one or more of sodium sulfate, sodium chloride, sodium carbonate, and sodium bicarbonate.

5. The method for preparing a Prussian blue positive electrode material according to claim 4, characterized in that: The solute concentration of the A solution is 0.1-0.5 mol / L, the solute concentration of the B solution is 0.5-3 mol / L, and the solute concentration of the C solution is 2-20 mol / L.

6. The method for preparing a Prussian blue positive electrode material according to claim 1, characterized in that: In the granulation kettle described in S2, the reaction temperature is 20~70°C, in the growth kettle described in S3, the reaction temperature is 20~50°C; in the aging kettle described in S4, during the aging process, the reaction temperature is 50~80°C.

7. The method for preparing a Prussian blue positive electrode material according to claim 1, characterized in that: The stirring speed of the granulation kettle described in S2 is 200~700 rpm; the stirring speed of the growth kettle described in S3 is 200~600 rpm; in the aging kettle described in S4, the stirring speed during the aging process is 100~400 rpm.

8. A method for preparing a Prussian blue positive electrode material according to any one of claims 6 or 7, characterized in that: S3-S4 respectively include the following empty kettle startup steps of the growth kettle and the aging kettle: Before the growth kettle receives the first mixed liquid overflowing from the granulation kettle, and before the aging kettle receives the second mixed liquid overflowing from the growth kettle, water is added to the growth kettle and the aging kettle respectively, so that the stirring devices in the growth kettle and the aging kettle are both placed in water.

9. The method for preparing a Prussian blue positive electrode material according to claim 1, characterized in that: After the particle size of the first mixed liquid meets the standard, the residence time of the first mixed liquid in the granulation kettle is 0.5~10 hours; after the particle size of the second mixed liquid meets the standard, the residence time of the second mixed liquid in the growth kettle is 4~24 hours; the aging time in the aging kettle is 2~12 hours.

10. A Prussian blue positive electrode material, characterized in that: The cathode material is prepared by the method for preparing a Prussian blue cathode material as described in any one of claims 1 to 9.