A Prussian blue-based cathode material, its heterogeneous nucleation preparation method and application, and its use as a cathode material for sodium-ion batteries and sodium-ion batteries.

Abstract

This invention discloses a Prussian blue-like cathode material, its heterogeneous nucleation preparation method and application, and its use as a cathode material for sodium-ion batteries and sodium-ion batteries, belonging to the field of inorganic functional material preparation technology. Method: Under stirring conditions, an aqueous solution containing zinc ions is added to an aqueous solution containing ferrocyanide ions and mixed. Under a protective atmosphere, a solution containing sodium ions and a solution containing ferrous ions are simultaneously and independently added dropwise to a suspension of zinc ferrocyanide crystal nuclei obtained under stirring conditions. The reaction is continued with stirring, then stirring is stopped, and the mixture is allowed to age under a protective atmosphere. The aged product is centrifuged, washed, dried, and ground to obtain the product. When the Prussian blue analogue synthesized using this method is used as a cathode material for sodium-ion batteries, it exhibits excellent electrochemical performance. This invention has a simple process and good reproducibility, providing an effective route for the preparation of key materials for high-performance sodium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of inorganic functional material preparation technology, specifically to a Prussian blue-based cathode material, its heterogeneous nucleation preparation method and application, as well as a sodium-ion battery cathode and a sodium-ion battery. Background Technology

[0002] Prussian blue and its analogues, due to their unique open-framework structure, high specific surface area, and tunable redox activity, show broad application prospects in electrochemical energy storage, catalysis, sensing, and biomedicine. In particular, as cathode materials for sodium-ion or potassium-ion batteries, their crystal size and morphology significantly affect the ion diffusion rate and the cycle stability of the material.

[0003] Currently, the conventional method for synthesizing Prussian blue and its analogues is the coprecipitation method, which involves directly mixing and reacting an iron source with a cyanide source in solution. However, this method suffers from drawbacks such as difficulty in controlling the nucleation process, high nucleation barriers, and a small number and non-uniform size of crystal nuclei. This results in Prussian blue crystals that are generally small in size, widely distributed, and prone to generating a large number of lattice defects and interstitial water, which is detrimental to the full realization of its electrochemical performance.

[0004] Therefore, how to develop a simple method to effectively regulate the nucleation and growth kinetics of Prussian blue and achieve the synthesis of large-size, high-quality crystals has become an urgent problem to be solved in this field. Summary of the Invention

[0005] In view of this, the present invention provides a Prussian blue-type cathode material, its heterogeneous nucleation preparation method and application, as well as a sodium-ion battery cathode and a sodium-ion battery.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a Prussian blue-based cathode material through heterogeneous nucleation includes the following steps:

[0008] (1) Under stirring conditions, an aqueous solution containing zinc ions is added to an aqueous solution containing ferrocyanide ions and mixed to obtain a zinc ferrocyanide crystal nucleus suspension;

[0009]

[0010] (2) Under a protective atmosphere, the solution containing sodium ions and the solution containing ferrous ions are simultaneously and independently added dropwise to the zinc ferrocyanide crystal nucleus suspension obtained in step (1) under stirring conditions. After the addition is completed, the reaction is stirred and then the stirring is stopped. The mixture is allowed to stand and age under a protective atmosphere.

[0011]

[0012] (3) Centrifuge, wash, dry and grind the product after aging in step (2) to obtain the Prussian blue cathode material.

[0013] Furthermore, in step (1), the stirring speed is 600 rpm and the mixing temperature is 20-60℃;

[0014] The aqueous solution containing ferrocyanide ions is an aqueous solution of one or both of potassium ferrocyanide or sodium ferrocyanide.

[0015] The aqueous solution containing zinc ions is an aqueous solution of one or two of zinc sulfate, zinc chloride, or zinc nitrate.

[0016] Step (1) Under stirring conditions, 50 mL of an aqueous solution containing zinc ions with a concentration of 0.01 mol / L is added to 50 mL of an aqueous solution containing ferrocyanide ions with a concentration of 0.1 mol / L and mixed to obtain a zinc ferrocyanide crystal nucleus suspension.

[0017] Step (2) Under a protective atmosphere, 180 mL of a 0.5 mol / L solution containing sodium ions and 45 mL of a 0.1 mol / L solution containing ferrous ions are simultaneously and independently added dropwise to the zinc ferrocyanide crystal nucleus suspension obtained in step (1) under stirring conditions.

[0018] Furthermore, in step (2), the method for preparing the solution containing sodium ions includes the following steps: adding 90 mmol NaCl, 0.045 mmol PVP and 0.1 g ascorbic acid to 180 mL distilled water, stirring thoroughly until all components are completely dissolved to obtain a solution containing sodium ions;

[0019] The preparation method of a solution containing ferrous ions includes the following steps: 4.5 mmol FeCl2·4H2O and 22.5 mmol trisodium citrate dihydrate powder are added to a sealed container and immediately sealed. The air in the container is completely replaced by repeatedly evacuating and filling with inert gas several times. Then, 45 mL of deoxygenated distilled water is slowly injected through a direct valve. The valve is closed, and the materials in the sealed container are stirred evenly. Finally, the mixture is allowed to stand and complex for 2 hours under a protective atmosphere to obtain a solution containing ferrous ions.

[0020] Furthermore, in step (2), the protective atmosphere is nitrogen or argon; the solution containing sodium ions and the solution containing ferrous ions are added dropwise at a flow rate of 1 mL / min by a peristaltic pump.

[0021] Furthermore, in step (2), after the addition is complete, continue stirring for 0.5-1 hour at a stirring speed of 600 rpm, and let it stand and age for 6-12 hours under a protective atmosphere.

[0022] Further, in step (3), the centrifugation speed is 10000 rpm, the centrifugation time is 10 minutes, the supernatant is discarded, the precipitate is washed three times with deionized water by centrifugation, and after each washing, deionized water is added and sonicated to redisperse the precipitate. The last wash uses a water-ethanol mixture with a volume ratio of 1:1, and all products are collected in the same centrifuge tube and placed in a vacuum drying oven. The oven is evacuated to 100-200 Pa and the drying temperature is maintained at 100-120℃. The vacuum drying time is 12 hours, and the particles are ground to a particle size of 1-2 micrometers.

[0023] The present invention also provides a Prussian blue cathode material prepared by the preparation method described above. The Prussian blue cathode material has a cubic phase structure, a primary particle size of 1-2 micrometers, a sodium content of not less than 1.82%, a vacancy defect rate of not more than 5%, and a water of crystallization of not more than 0.74%.

[0024] The present invention also provides an application of the Prussian blue-based cathode material as a cathode active material in sodium-ion batteries.

[0025] The present invention also provides a sodium-ion battery cathode, comprising the Prussian blue cathode material as the cathode active material.

[0026] The present invention also provides a sodium-ion battery, including the positive electrode of the sodium-ion battery.

[0027] Compared with existing technologies, the beneficial effects of this invention are as follows: The method of this invention introduces explosive nucleation of zinc ferrocyanide, and the resulting zinc ferrocyanide crystal nuclei provide a large number of high-surface-energy heterogeneous nucleation sites for subsequent reactions. This significantly reduces the nucleation barrier required for sodium hexacyanoferrate molecule deposition, allowing it to preferentially deposit directionally on the crystal nucleus surface rather than undergoing random homogeneous nucleation in solution. This controlled heterogeneous nucleation and growth process effectively guides the crystal growth of Prussian blue, promoting the formation of crystals with significantly increased size and higher crystallinity. Therefore, the Prussian blue material synthesized using the method provided by this invention exhibits excellent physical properties and electrochemical performance, laying a solid material foundation for its practical applications in energy storage and other fields. The synthesis method described in this invention is simple, requiring only a pre-nucleation reaction before the conventional co-precipitation step. It does not require complex template agents, high temperature and pressure, or special equipment, is low in cost, and has strong repeatability and controllability, making it suitable for large-scale industrial production.

[0028] This method effectively lowers the nucleation barrier of Prussian blue by utilizing zinc ferrocyanide crystal nuclei, guiding the crystals to preferentially deposit and grow at out-of-phase points rather than undergoing random homogeneous nucleation in solution, thus achieving precise control over crystal nucleation and growth kinetics. When the Prussian blue analogue synthesized using this method is used as a cathode material for sodium-ion batteries, it exhibits excellent electrochemical performance, achieving a first-cycle discharge specific capacity of 117 mAh / g at 0.2 C rate and a capacity retention of 76.41% after 1500 cycles at 1 C rate. This invention features a simple process with good reproducibility, providing an effective route for the preparation of key materials for high-performance sodium-ion batteries. Attached Figure Description

[0029] Figure 1 The XRD pattern of the heterogeneous nucleated iron-based Prussian blue cathode material synthesized in Example 1 of this invention;

[0030] Figure 2 Here is a SEM image of the heterogeneous nucleated iron-based Prussian blue cathode material synthesized in Example 1 of this invention;

[0031] Figure 3 Here is a SEM image of the conventional nucleated iron-based Prussian blue cathode material synthesized in Comparative Example 1 of this invention;

[0032] Figure 4 The charge-discharge curves of the heterogeneous nucleated iron-based Prussian blue cathode material synthesized in Example 1 of this invention are shown at a rate of 0.5C.

[0033] Figure 5 The charge-discharge curves of the heterogeneous nucleated iron-based Prussian blue cathode material synthesized in Example 1 of this invention at a 2C rate are shown.

[0034] Figure 6 The charge-discharge curves of the conventional nucleated iron-based Prussian blue cathode material synthesized in Comparative Example 1 of this invention are shown at a rate of 0.5C.

[0035] Figure 7 The charge-discharge curves of the conventional nucleated iron-based Prussian blue cathode material synthesized in Comparative Example 1 of this invention at a 2C rate are shown.

[0036] Figure 8 The long-cycle performance of the heterogeneous nucleated iron-based Prussian blue cathode material synthesized in Example 1 of this invention at a 1C rate;

[0037] Figure 9 This invention demonstrates the long-cycle performance of the conventional nucleated iron-based Prussian blue cathode material synthesized in Comparative Example 1 at a 1C rate. Detailed Implementation

[0038] 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.

[0039] Example 1

[0040] A method for preparing Prussian blue-based cathode materials through heterogeneous nucleation includes the following steps:

[0041] (1) Accurately weigh 2.1783 g (5 mmol) sodium ferrocyanide (Na4Fe(CN)6·10H2O) and place it in a 100 mL clean and dry beaker. Add 40 mL of deionized water and stir thoroughly on a magnetic stirrer until the solid is completely dissolved. Quantitatively transfer the resulting solution to a 50 mL volumetric flask. Wash the inner wall of the beaker several times with a small amount of deionized water. Transfer the washing liquid into the volumetric flask as well. Finally, dilute to the mark with deionized water and shake well to obtain a 0.1 mol / L sodium ferrocyanide aqueous solution, labeled as solution A.

[0042] (2) Accurately weigh 0.1438 g (0.5 mmol) of zinc sulfate heptahydrate (ZnSO4·7H2O) and place it in a 100 mL clean beaker. Add 40 mL of deionized water and sonicate for 20 min to disperse it completely. Quantitatively transfer the solution to a 50 mL volumetric flask. Wash the beaker several times with a small amount of deionized water. Combine the washing liquids and transfer them to the volumetric flask. Finally, dilute to the mark and shake well to obtain a zinc sulfate aqueous solution with a concentration of 0.01 mol / L, labeled as solution B.

[0043] (3) At 25°C and under vigorous stirring at 600 rpm, solution B was quickly poured into solution A. The solution immediately became turbid, and a zinc ferrocyanide crystal nucleus suspension was obtained, which was labeled as solution C.

[0044] (4) Accurately weigh 5.2598 g (90 mmol) NaCl, 1.8 g (0.045 mmol) PVP, and 0.1 g ascorbic acid, place them in a 300 mL sealed reaction vessel, then add 180 mL of distilled water, and stir thoroughly on a magnetic stirrer until all components are completely dissolved to obtain a homogeneous 0.5 mol / L solution containing sodium ions, labeled as solution D;

[0045] (5) In a 100 mL sealed sample bottle, add 0.8942 g (4.5 mmol) FeCl2·4H2O and 6.6173 g (22.5 mmol) trisodium citrate dihydrate powder in advance and quickly, and seal immediately. Repeatedly evacuate and fill with nitrogen several times to completely replace the air in the bottle. Then, slowly inject 45 mL of deoxygenated distilled water through the straight valve, close the valve, place the sample bottle on a magnetic stirrer and stir evenly. Under nitrogen atmosphere, let it stand for 2 hours to complex and label it as solution E.

[0046] (6) Under a nitrogen atmosphere, solutions D and E were simultaneously and independently added dropwise to solution C under stirring conditions by a peristaltic pump at a flow rate of 1 mL / min. After the addition was completed, stirring was continued for 0.5 hours at a stirring speed of 600 rpm. Then stirring was stopped and the solution was allowed to stand and age for 12 hours under a nitrogen atmosphere.

[0047] (7) Centrifuge the aged product at 10,000 rpm for 10 minutes. Discard the supernatant. Wash the precipitate with deionized water three times by centrifugation. After each wash, add deionized water and sonicate to redisperse the precipitate. For the last wash, use a water-ethanol mixture with a volume ratio of 1:1. Collect all the products into the same centrifuge tube and place it in a vacuum drying oven. Evacuate the oven to 200 Pa and maintain the drying temperature at 120°C for 12 hours. Grind the material under a nitrogen atmosphere until the particle size is 1-2 micrometers to obtain heterogeneous nucleated iron-based Prussian blue cathode material.

[0048] (8) The obtained heterogeneous nucleated iron-based Prussian blue cathode material, conductive agent (Super P) and binder (PVDF) are mixed in a mass ratio of 7:2:1. An appropriate amount of N-methylpyrrolidone (NMP) is added and ground into a uniform slurry. The slurry is then coated onto the current collector. The coated electrode is vacuum dried at 120°C for 12 hours and then used as the cathode of a sodium-ion battery to assemble a sodium-ion battery.

[0049] like Figure 1 The image shows the X-ray diffraction pattern of the heterogeneous nucleated iron-based Prussian blue cathode material synthesized in Example 1. Figure 1 It can be seen that the obtained product has a typical cubic Prussian blue crystal structure. The dried electrode sheets were sliced, pressed, weighed and recorded, and then used for the assembly and testing of sodium-ion batteries.

[0050] like Figure 2 As shown, it is a scanning electron microscope image of the material synthesized in Example 1. Figure 2As can be seen, the obtained heterogeneous nucleated iron-based Prussian blue cathode material consists of micron-sized particles with a primary particle size of approximately 1–2 micrometers. This indicates that the heterogeneous nucleation strategy effectively reduces the nucleation barrier and promotes the formation of large-sized crystals. Further compositional analysis shows that the material has a high sodium content (Na content of 1.82, theoretical value of 2), a low vacancy defect rate (5%), and only 0.74 units of water of crystallization, demonstrating excellent structural integrity.

[0051] Example 1: Electrochemical performance test results of sodium-ion batteries are as follows Figure 4 , 5 As shown in Figure 8, the test results show that the synthesized heterogeneous iron-based nucleated Prussian blue cathode material has excellent electrochemical capacity and rate performance: the first discharge specific capacity reaches 118 mAh / g at 0.5C rate, and it can still maintain a discharge specific capacity of 99 mAh / g at 2C high rate. The capacity retention rate after 1500 cycles at 1C is as high as 76.41%.

[0052] Comparative Example 1

[0053] (1) Following the same steps as in Example 1 (1), solution A is obtained;

[0054] (2) Following the same procedure as in Example 1 (4), solution D is obtained;

[0055] (3) Following the same procedure as in Example 1 (5), solution E is obtained;

[0056] (4) Under a nitrogen atmosphere, solutions D and E are simultaneously and independently added dropwise to solution A under stirring conditions by a peristaltic pump at a flow rate of 1 mL / min. After the addition is completed, stirring is continued for 0.5 hours at a stirring speed of 600 rpm. Then stirring is stopped and the solution is allowed to stand and age for 12 hours under a nitrogen atmosphere.

[0057] (5) Following the same steps (7) as in Example 1, conventional nucleated iron-based Prussian blue cathode materials are obtained.

[0058] (6) The conventional nucleated iron-based Prussian blue cathode material, conductive agent (Super P) and binder (PVDF) are mixed in a mass ratio of 7:2:1. An appropriate amount of N-methylpyrrolidone (NMP) is added and ground into a uniform slurry. The slurry is then coated onto the current collector. The coated electrode is then vacuum dried at 120°C for 12 hours.

[0059] like Figure 3 As shown, it is a scanning electron microscope image of the conventional nucleated iron-based Prussian blue cathode material synthesized in Comparative Example 1. Figure 3As can be seen, the obtained conventional nucleated iron-based Prussian blue cathode material consists of micron-sized particles, with small crystal size (approximately 0.5 micrometers) and non-uniform morphology. Analysis shows that the material has a low sodium content (Na content of 1.53%), a high vacancy defect rate (9%), and a high amount of water of crystallization of 0.94.

[0060] The conventional nucleated iron-based Prussian blue cathode material synthesized in Comparative Example 1 was used as the cathode material in the assembly of a sodium-ion battery, and the electrochemical performance test results are as follows: Figure 6 , 7 and Figure 9 As shown. Figure 6 and Figure 7 The figures show the charge-discharge curves of the material at 0.5C and 2C rates, respectively. The test results indicate that the synthesized conventional nucleated iron-based Prussian blue cathode material exhibits significantly worse electrochemical capacity and rate performance than Example 1: the first-cycle discharge specific capacity at 0.5C is 107 mAh / g, the first-cycle discharge specific capacity at 2C is 93 mAh / g, and the capacity retention after 1500 cycles at 1C is only 43.61%.

[0061] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a Prussian blue-based cathode material through heterogeneous nucleation, characterized in that, Includes the following steps: (1) Under stirring conditions, an aqueous solution containing zinc ions is added to an aqueous solution containing ferrocyanide ions and mixed to obtain a zinc ferrocyanide crystal nucleus suspension; (2) Under a protective atmosphere, the solution containing sodium ions and the solution containing ferrous ions are simultaneously and independently added dropwise to the zinc ferrocyanide crystal nucleus suspension obtained in step (1) under stirring conditions. After the addition is completed, the reaction is stirred and then the stirring is stopped. The mixture is allowed to stand and age under a protective atmosphere. (3) Centrifuge, wash, dry and grind the product after aging in step (2) to obtain the Prussian blue cathode material; In step (1), the stirring speed is 600 rpm and the mixing temperature is 20-60℃; The aqueous solution containing ferrocyanide ions is an aqueous solution of one or both of potassium ferrocyanide or sodium ferrocyanide. The aqueous solution containing zinc ions is an aqueous solution of one or two of zinc sulfate, zinc chloride, or zinc nitrate. Step (1) Under stirring conditions, 50 mL of an aqueous solution containing zinc ions with a concentration of 0.01 mol / L is added to 50 mL of an aqueous solution containing ferrocyanide ions with a concentration of 0.1 mol / L and mixed to obtain a zinc ferrocyanide crystal nucleus suspension. Step (2) Under a protective atmosphere, 180 mL of a 0.5 mol / L solution containing sodium ions and 45 mL of a 0.1 mol / L solution containing ferrous ions are simultaneously and independently added dropwise to the zinc ferrocyanide crystal nucleus suspension obtained in step (1) under stirring conditions. The Prussian blue cathode material has a cubic phase structure.

2. The method for preparing a Prussian blue-type cathode material by heterogeneous nucleation according to claim 1, characterized in that, In step (2), the method for preparing the solution containing sodium ions includes the following steps: adding 90 mmol NaCl, 0.045 mmol PVP and 0.1 g ascorbic acid to 180 mL distilled water, stirring thoroughly until all components are completely dissolved to obtain a solution containing sodium ions; The preparation method of a solution containing ferrous ions includes the following steps: 4.5 mmol FeCl2·4H2O and 22.5 mmol trisodium citrate dihydrate powder are added to a sealed container and immediately sealed. The air in the container is completely replaced by repeatedly evacuating and filling with inert gas several times. Then, 45 mL of deoxygenated distilled water is slowly injected through a direct valve. The valve is closed, and the materials in the sealed container are stirred evenly. Finally, the mixture is allowed to stand and complex for 2 hours under a protective atmosphere to obtain a solution containing ferrous ions.

3. The method for preparing a Prussian blue-type cathode material by heterogeneous nucleation according to claim 1, characterized in that, In step (2), the protective atmosphere is nitrogen or argon; the solution containing sodium ions and the solution containing ferrous ions are added dropwise at a flow rate of 1 mL / min by a peristaltic pump.

4. The method for preparing a Prussian blue-type cathode material by heterogeneous nucleation according to claim 1, characterized in that, In step (2), after the addition is complete, continue stirring for 0.5-1 hour at a stirring speed of 600 rpm, and let it stand and age for 6-12 hours under a protective atmosphere.

5. The method for preparing a Prussian blue-type cathode material by heterogeneous nucleation according to claim 1, characterized in that, In step (3), the centrifugation speed is 10000 rpm and the centrifugation time is 10 minutes. The supernatant is discarded and the precipitate is washed three times with deionized water. After each washing, deionized water is added and sonicated to redisperse the precipitate. The last washing uses a water-ethanol mixture with a volume ratio of 1:

1. All products are collected in the same centrifuge tube and placed in a vacuum drying oven. The oven is evacuated to 100-200 Pa and the drying temperature is maintained at 100-120℃. The vacuum drying time is 12 hours. The particles are ground to a particle size of 1-2 micrometers.

6. A Prussian blue-based cathode material prepared by the preparation method according to any one of claims 1-5, characterized in that, Its primary particle size is 1-2 micrometers, and the sodium content of the Prussian blue cathode material is not less than 1.82%, the vacancy defect rate is not higher than 5%, and the amount of water of crystallization is not higher than 0.74%.

7. The application of the Prussian blue-based cathode material as described in claim 6 as a cathode active material in a sodium-ion battery.

8. A sodium-ion battery positive electrode, characterized in that, The Prussian blue-based cathode material described in claim 6 is included as the cathode active material.

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

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