Prussian blue positive electrode material and preparation method and application thereof

Abstract

The application relates to the field of sodium ion batteries, in particular to a Prussian blue positive electrode material and a preparation method and application thereof; the preparation method steps comprise the following: S1, a proper amount of a chelating agent is weighed and dissolved in a ferric chloride solution to prepare a first mixed solution; S2, a proper amount of sodium ferrocyanide decahydrate is weighed and dissolved in a saturated sodium chloride solution to prepare a second mixed solution; S3, the first mixed solution and the second mixed solution are subjected to freezing treatment and crushing treatment in sequence to prepare a first powder and a second powder; S4, the first powder and the second powder are mixed uniformly in a low-temperature environment, then stirring reaction is carried out under the protection of inert gas, and centrifugal treatment is carried out; S5, the precipitate obtained through the centrifugal treatment is subjected to washing treatment and freeze-drying treatment, and a Prussian blue positive electrode material is obtained; the application provides the Prussian blue positive electrode material with high crystallinity; through freezing and crushing, the chelating agent is slowly released, Prussian blue vacancies are relieved, and the crystallinity of the Prussian blue is improved at low temperature.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion batteries, and more particularly to a Prussian blue cathode material, its preparation method, and its application. Background Technology

[0002] With the depletion of fossil fuels, other renewable energy sources such as wind and solar power have developed rapidly. However, these renewable energy sources are highly intermittent and have weak energy conversion and storage capabilities, limiting their application. Sodium-ion batteries, due to their abundant resources and low cost, have become the best candidate for energy storage systems.

[0003] Prussian blue and its analogues, which possess large 3D ion channels, facilitate the insertion and extraction of sodium ions, making them ideal cathode materials for sodium-ion batteries. However, the presence of numerous vacancies and coordinated water in the crystal structure of these materials occupies many electrochemical reaction sites. Furthermore, the presence of vacancies can cause structural collapse due to the migration of sodium ions, and the coordinated water in the structure reduces the conductivity of the material. Consequently, the material often exhibits low cycle stability and rate performance in practical applications. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a Prussian blue cathode material, its preparation method, and its applications.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first aspect of this invention is to provide a method for preparing a Prussian blue cathode material, comprising the steps of:

[0007] S1. Weigh an appropriate amount of chelating agent and dissolve it in ferric chloride solution, stir evenly, and prepare the first mixed solution;

[0008] S2. Weigh an appropriate amount of sodium ferrocyanide decahydrate and dissolve it in a saturated sodium chloride solution. Stir well to obtain a second mixed solution.

[0009] S3. The first mixed solution and the second mixed solution are subjected to freezing treatment and pulverization treatment respectively to obtain the first powder and the second powder.

[0010] S4. After mixing the first powder and the second powder evenly in a low-temperature environment, stir and react under inert gas protection and then centrifuge.

[0011] S5. The precipitate obtained by centrifugation is washed and freeze-dried to obtain the Prussian blue cathode material.

[0012] Preferably, in step S1, the molar mass of the chelating agent is 0.1 mol to 0.2 mol.

[0013] Preferably, in step S1, the chelating agent is sodium citrate and sodium carboxymethyl cellulose; the molar ratio of sodium citrate to sodium carboxymethyl cellulose is 1:(1~1.5).

[0014] Preferably, in step S3, the freezing temperature is -35℃ to -28℃, and the freezing time is 12h to 24h.

[0015] Preferably, in step S4, the temperature of the low-temperature environment is -10℃ to 0℃.

[0016] Preferably, in step S4, the stirring rate of the stirring reaction is 800 r / min, and the stirring reaction time is 23 h to 28 h.

[0017] Preferably, in step S4, the inert gas is nitrogen.

[0018] Preferably, in step S5, the washing process includes: washing the precipitate sequentially with deionized water and ethanol; the number of times the deionized water is washed is ≥3, and the number of times the ethanol is washed is >1.

[0019] Preferably, in step S5, the freeze-drying temperature is -60℃ to -40℃, and the freeze-drying time is 60h to 72h.

[0020] A second aspect of the present invention is to provide a Prussian blue cathode material prepared by the above-described preparation method.

[0021] A third aspect of the present invention is to provide a sodium-ion battery, comprising: a positive electrode shell, a positive electrode sheet, a first electrolyte, a separator, a second electrolyte, a negative electrode sheet, a gasket, and a negative electrode shell arranged sequentially; wherein the positive electrode sheet is composed of the Prussian blue positive electrode material, the conductive agent Super-P, VGCF, and the binder PVDF in a mass ratio of 8:0.5:0.5:1; the Prussian blue positive electrode material is prepared by the above preparation method or as described above.

[0022] Preferably, the negative electrode is a sodium electrode.

[0023] Preferably, both the first electrolyte and the second electrolyte are 1 mol / L NaPF6 solutions; the solvents of the NaPF6 solution are EC and DEC.

[0024] More preferably, in the solvent, the volume ratio of EC to DEC is 1:1.

[0025] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0026] (1) The present invention provides a Prussian blue cathode material with high crystallinity, less structural defects and water content, which is used as the cathode of sodium-ion batteries, so that sodium-ion batteries have good cycle performance and stability.

[0027] (2) After cryogenic pulverization, the chelating agent is released slowly, which can effectively alleviate the problem of Prussian blue vacancies.

[0028] (3) Low temperature will slow down the nucleation and precipitation of Prussian blue and increase the crystallinity of Prussian blue. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0031] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0032] Example 1

[0033] This embodiment provides a method for preparing Prussian blue cathode material, the steps of which include:

[0034] S1. Weigh 0.1 mol of chelating agent and dissolve it in 100 mL of ferric chloride solution, stir well to obtain the first mixed solution; the chelating agent is sodium citrate and sodium carboxymethyl cellulose (molar ratio of 1:1);

[0035] S2. Weigh an appropriate amount of sodium ferrocyanide decahydrate and dissolve it in 100 mL of saturated sodium chloride solution. Stir well to obtain the second mixed solution.

[0036] S3. The first mixed solution and the second mixed solution are subjected to freezing treatment and pulverization treatment respectively to obtain the first powder and the second powder; the freezing treatment temperature is -30℃ and the freezing treatment time is 12h;

[0037] S4. After mixing the first powder and the second powder evenly in a low temperature environment of -10℃, stir and react at a speed of 800r / min for 28h under nitrogen protection, and then centrifuge.

[0038] S5. The precipitate obtained by centrifugation is washed three times with deionized water, then washed twice with ethanol, and finally freeze-dried at -60°C for 60 hours to obtain the Prussian blue cathode material.

[0039] Example 2

[0040] This embodiment provides another method for preparing Prussian blue cathode material, the steps of which include:

[0041] S1. Weigh 0.1 mol of chelating agent and dissolve it in 100 mL of ferric chloride solution, stir well to obtain the first mixed solution; the chelating agent is sodium citrate and sodium carboxymethyl cellulose (molar ratio of 1:1.5);

[0042] S2. Weigh an appropriate amount of sodium ferrocyanide decahydrate and dissolve it in 100 mL of saturated sodium chloride solution. Stir well to obtain the second mixed solution.

[0043] S3. The first mixed solution and the second mixed solution are subjected to freezing treatment and pulverization treatment respectively to obtain the first powder and the second powder; the freezing treatment temperature is -30℃ and the freezing treatment time is 12h;

[0044] S4. After mixing the first powder and the second powder evenly in a low temperature environment of -5℃, stir and react at a speed of 800r / min for 25h under nitrogen protection, and then centrifuge.

[0045] S5. The precipitate obtained by centrifugation is washed three times with deionized water, then washed twice with ethanol, and finally freeze-dried at -50°C for 65 hours to obtain the Prussian blue cathode material.

[0046] Example 3

[0047] This embodiment provides another method for preparing Prussian blue cathode material, the steps of which include:

[0048] S1. Weigh 0.1 mol of chelating agent and dissolve it in 100 mL of ferric chloride solution, stir well to obtain the first mixed solution; the chelating agent is sodium citrate and sodium carboxymethyl cellulose (molar ratio of 1:1.2);

[0049] S2. Weigh an appropriate amount of sodium ferrocyanide decahydrate and dissolve it in 100 mL of saturated sodium chloride solution. Stir well to obtain the second mixed solution.

[0050] S3. The first mixed solution and the second mixed solution are subjected to freezing treatment and pulverization treatment respectively to obtain the first powder and the second powder; the freezing treatment temperature is -30℃ and the freezing treatment time is 24h;

[0051] S4. After mixing the first powder and the second powder evenly in a low temperature environment of 0°C, stir and react at a speed of 800r / min for 25h under nitrogen protection, and then centrifuge.

[0052] S5. The precipitate obtained by centrifugation is washed three times with deionized water, then washed twice with ethanol, and finally freeze-dried at -40°C for 72 hours to obtain the Prussian blue cathode material.

[0053] Example 4

[0054] This embodiment provides a sodium-ion battery, comprising: a positive electrode shell, a positive electrode sheet, a first electrolyte, a separator, a second electrolyte, a negative electrode sheet, a gasket, and a negative electrode shell arranged sequentially; wherein, the positive electrode sheet is composed of Prussian blue positive electrode material, conductive agent Super-P, VGCF, and binder PVDF in a mass ratio of 8:0.5:0.5:1; the negative electrode sheet is a sodium sheet; the first electrolyte and the second electrolyte are both 1 mol / L NaPF6 solutions; the solvent of the NaPF6 solution is EC and DEC (the volume ratio of EC to DEC is 1:1); the Prussian blue positive electrode material is prepared using the preparation method described in Example 1.

[0055] Comparative Example

[0056] This comparative example provides a method for preparing Prussian blue cathode material, the steps of which include:

[0057] Dissolve 0.05 mol each of sodium citrate and sodium carboxymethyl cellulose in beaker A containing 100 mL of ferric chloride solution. Then, weigh out sodium ferrocyanide decahydrate and dissolve it in beaker B containing 100 mL of saturated sodium chloride solution. Stir until homogeneous to form mixed solutions A and B. Slowly add mixed solution A dropwise to mixed solution B, stirring at 800 rpm for 18–24 h, and centrifuge. The entire reaction process is protected with nitrogen (N2) to prevent Fe from reacting. 2+ To prevent oxidation, the precipitate after centrifugation is washed multiple times with deionized water and ethanol, and then freeze-dried.

[0058] Detection Examples

[0059] Prussian blue cathode materials prepared by the preparation methods described in Examples 1-3 and Prussian blue cathode materials prepared by the preparation method described in the comparative example were combined with conductive agents and binders to prepare cathode sheets. Batteries were prepared by assembling cathode shell, cathode sheet, electrolyte, separator, electrolyte, negative electrode sheet, gasket, and negative electrode shell in that order. After the batteries were left to stand at room temperature for 2-3 hours, performance tests were conducted. The test results are shown in Table 1.

[0060] Table 1

[0061]

[0062] In summary, this invention provides a highly crystalline Prussian blue cathode material with fewer structural defects and water content, which is suitable for use as the cathode in sodium-ion batteries, resulting in good cycle performance and stability. After cryogenic pulverization, the chelating agent is slowly released, which can effectively alleviate the problem of Prussian blue vacancies. Low temperature slows down the nucleation and precipitation rate of Prussian blue, thereby increasing its crystallinity.

[0063] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A method for preparing a Prussian blue cathode material, characterized in that the steps include... include: S1. Weigh an appropriate amount of chelating agent and dissolve it in ferric chloride solution, stir evenly, and prepare the first mixed solution; S2. Weigh an appropriate amount of sodium ferrocyanide decahydrate and dissolve it in a saturated sodium chloride solution. Stir well to obtain a second mixed solution. S3. The first mixed solution and the second mixed solution are subjected to freezing treatment and pulverization treatment respectively to obtain the first powder and the second powder; the freezing treatment temperature is -35℃ to -28℃ and the freezing treatment time is 12h to 24h. S4. The first powder and the second powder are mixed evenly in a low-temperature environment, and then stirred and reacted under inert gas protection and centrifuged to obtain a precipitate; the temperature of the low-temperature environment is -10℃ to 0℃. S5. The precipitate obtained by centrifugation is washed and freeze-dried to obtain the Prussian blue cathode material; the freeze-drying temperature is -60℃ to -40℃ and the freeze-drying time is 60h to 72h.

2. The preparation method according to claim 1, characterized in that, In step S1, the molar mass of the chelating agent is 0.1 mol to 0.2 mol.

3. The preparation method according to claim 1, characterized in that, In step S1, the chelating agent is sodium citrate and sodium carboxymethyl cellulose; the molar ratio of sodium citrate to sodium carboxymethyl cellulose is 1:(1~1.5).

4. The preparation method according to claim 1, characterized in that, In step S4, the stirring rate of the stirring reaction is 800 r / min, and the stirring reaction time is 23 h to 28 h.

5. The preparation method according to claim 1, characterized in that, In step S5, the washing process includes: washing the precipitate sequentially with deionized water and ethanol; the number of times the precipitate is washed with deionized water is ≥3, and the number of times the ethanol is washed is >1.

6. A Prussian blue cathode material prepared by the preparation method according to any one of claims 1-5.

7. A sodium-ion battery, characterized in that, include: The positive electrode shell, positive electrode sheet, first electrolyte, separator, second electrolyte, negative electrode sheet, gasket, and negative electrode shell are arranged sequentially; the positive electrode sheet is composed of the Prussian blue positive electrode material, conductive agent Super-P, VGCF, and binder PVDF in a mass ratio of 8:0.5:0.5:1; the Prussian blue positive electrode material is prepared by the preparation method according to any one of claims 1-5 or as described in claim 6.

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