A prussian blue complex and preparation method and use thereof

Abstract

The application discloses a Prussian blue compound and a preparation method and application thereof, and the preparation method is as follows: (1) uniformly dispersing a carbon source / nitrogen source, an iron salt and a nickel salt in ethanol, drying, and calcining under an inert atmosphere to obtain FeNi@NCT; (2) dispersing the FeNi@NCT in a sodium ferrocyanide aqueous solution, adjusting pH, standing, washing with deionized water, and drying to obtain a Prussian blue compound, and the Prussian blue compound is also called FeNiPBA / NCT. The preparation method is simple, efficient, green, has strong component adjustability, strong process scalability and is easy to enlarge. The Prussian blue compound prepared by the application has high crystallinity and high conductivity, as a positive electrode material, significantly improves the rate performance and cycle life of a sodium ion battery, and the electrochemical performance far exceeds that of a conventional modified strategy for preparing a Prussian blue positive electrode material, and overcomes the technical defects of the Prussian blue positive electrode material in the sodium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of battery cathode material synthesis technology, specifically relating to a Prussian blue composite, its preparation method, and its uses. Background Technology

[0002] Due to the widespread availability and low cost of sodium metal resources, rechargeable sodium-ion batteries have become a highly promising candidate for large-scale energy storage systems. Prussian blue analogues (PBAs) are ideal cathode materials for sodium-ion batteries due to their 3D open framework and multiple redox sites. However, low crystallinity, lattice strain accumulation, and slow ion / electron transport limit the rate performance and cycle stability of PBAs.

[0003] To address the aforementioned issues, several strategies have been proposed, including slowing down the synthesis reaction rate (NanoLett. 2022, 22, 1302–1310), inert metal doping (Adv. Funct. Mater. 2024, 34, 2314167), and carbon-based material composites (Adv. Energy Mater. 2024, 14, 2303015). However, a single strategy cannot comprehensively improve electrochemical performance. For example, improved crystallinity limits electronic conductivity, strain suppression results in a loss of intrinsic capacity, and composite construction leads to limitations in scalability. Summary of the Invention

[0004] The first objective of this invention is to overcome the shortcomings of the prior art and provide a Prussian blue complex.

[0005] The second objective of this invention is to provide a method for preparing a Prussian blue complex.

[0006] A third objective of this invention is to provide the use of a Prussian blue complex in the preparation of sodium-ion batteries.

[0007] The technical solution of this invention is summarized as follows:

[0008] A method for preparing a Prussian blue complex includes the following steps:

[0009] (1) Disperse the carbon source / nitrogen source, iron salt, and nickel salt uniformly in ethanol, dry them, and calcine them under an inert atmosphere to obtain FeNi@NCT; (2) Disperse the FeNi@NCT in an aqueous solution of sodium ferrocyanide, adjust the pH to 0.5-3 with hydrochloric acid, let it stand, wash it with deionized water, and dry it to obtain the Prussian blue complex, also known as FeNiPBA / NCT.

[0010] Preferably, the cation molar ratio of the iron salt and nickel salt in step (1) is 1-3:1, and the mass of the carbon source / nitrogen source is 2-4 times the total mass of the iron salt and nickel salt.

[0011] Preferably, the carbon / nitrogen source is melamine, urea, or dicyandiamide.

[0012] Preferably, the anions of the iron salt include chloride, sulfate, nitrate or acetate ions.

[0013] Preferably, the anion of the nickel salt includes chloride, sulfate, nitrate or acetate.

[0014] Preferably, the inert atmosphere is argon or nitrogen, the calcination temperature is 700-900℃, and the calcination time is 1 hour.

[0015] Preferably, the ratio of FeNi@NCT to a 0.02 mol / L sodium ferrocyanide aqueous solution is 1 g: 10-100 mL.

[0016] Preferably, the pH is 1, and the standing time is 12-36 hours;

[0017] A Prussian blue complex prepared by the above preparation method.

[0018] The above-mentioned Prussian blue composite is used in the preparation of sodium-ion battery cathodes.

[0019] Beneficial effects

[0020] The preparation method of this invention is simple, efficient, green, and pollution-free. It offers strong component tunability, high process scalability, and ease of scale-up, making it suitable for the production of materials in various other fields. The highly crystalline and highly conductive Prussian blue composite prepared by this invention, as a cathode material, significantly improves the rate performance and cycle life of sodium-ion batteries. Its electrochemical performance far surpasses that of Prussian blue cathode materials prepared using conventional modification strategies, overcoming the current technical shortcomings of Prussian blue cathode materials in sodium-ion batteries. Attached Figure Description

[0021] Figure 1 The images show the SEM images (a) and elemental distribution diagram (b) of FeNiPBA / NCT obtained in Example 1.

[0022] Figure 2 The images show the SEM images of FeNi@NCT (a), FePBA (b), and FeNiPBA (c) obtained in Comparative Examples 1-3.

[0023] Figure 3 The images show a comparison of the XRD patterns of the samples obtained in Example 1 and Comparative Examples 1-3.

[0024] Figure 4 The TGA comparison images are of the samples obtained in Example 1 and Comparative Examples 2-3.

[0025] Figure 5 This is a comparison chart of the rate performance of the samples obtained in Example 1 and Comparative Examples 2-3.

[0026] Figure 6 The electrochemical impedance spectroscopy (EIS) of the samples obtained in Example 1 and Comparative Examples 2-3 is shown as a comparison.

[0027] Figure 7 The graph shows a comparison of the diffusion coefficients fitted by constant flow intermittent titration tests on the samples obtained in Example 1 and Comparative Examples 2-3.

[0028] Figure 8 The graph shows a comparison of the long-cycle constant current charge-discharge performance of the samples obtained in Example 1 and Comparative Examples 1-3. Detailed Implementation

[0029] The technical solution of the present invention will be further described below with reference to specific embodiments. It should be noted that the following embodiments are only used for detailed description and explanation of the present invention, and the application scope of the present invention is not limited by the conditions in the embodiments.

[0030] Example 1

[0031] A method for preparing a Prussian blue complex includes the following steps:

[0032] (1) 3.528 g of melamine, 6 mmol (0.788 g) of anhydrous ferrous chloride and 3 mmol (0.388 g) of anhydrous nickel chloride were uniformly dispersed in 60 mL of ethanol, dried at 80 °C and calcined at 800 °C under a nitrogen atmosphere for 2 hours to obtain FeNi@NCT;

[0033] (2) Disperse 1g of FeNi@NCT in 50mL of 0.02mmol / L sodium ferrocyanide aqueous solution, adjust the pH to 1 with hydrochloric acid, let stand for 24 hours, wash with deionized water, and vacuum dry at 120℃ for 12 hours to obtain black Prussian blue composite powder. The Prussian blue composite is also known as FeNiPBA / NCT, where FeNiPBA is Prussian blue crystal and NCT is nitrogen-doped carbon nanotubes. (Anhydrous ferric chloride can also be used to replace anhydrous ferrous chloride. Other steps follow the same procedure as in this example to obtain black Prussian blue composite powder.)

[0034] FeNiPBA / NCT powder morphology as follows Figure 1 As shown in Figure a, FeNiPBA is uniformly distributed on NCT, the hollow nitrogen-doped carbon nanotubes have an inner diameter of 400-600 nm, the Prussian blue grain size is 40-60 nm, and Fe, Ni, C, N, and Na elements are uniformly distributed in the sample (see Figure a). Figure 1 b).

[0035] Example 2

[0036] A method for preparing a Prussian blue complex includes the following steps:

[0037] (1) 4.868 g of urea, 4.5 mmol (1.251 g) of ferrous sulfate and 4.5 mmol (1.183 g) of nickel sulfate were uniformly dispersed in 60 mL of ethanol, dried at 80 °C and calcined at 900 °C under a nitrogen atmosphere for 3 hours to obtain FeNi@NCT;

[0038] (2) Disperse 1g FeNi@NCT in 10mL of 0.02mmol / L sodium ferrocyanide aqueous solution, adjust pH=0.5 with hydrochloric acid, let stand for 36 hours, wash with deionized water, and vacuum dry at 120℃ for 12 hours to obtain black Prussian blue complex powder, the Prussian blue complex is also known as FeNiPBA / NCT.

[0039] Example 3

[0040] A method for preparing a Prussian blue complex includes the following steps:

[0041] (1) 13.524 g of dicyandiamide, 6.75 mmol (2.727 g) of ferric nitrate and 2.25 mmol (0.654 g) of nickel nitrate were uniformly dispersed in 60 mL of ethanol, dried at 80 °C and calcined at 700 °C under an argon atmosphere for 1 hour to obtain FeNi@NCT;

[0042] (2) Disperse 1g FeNi@NCT in 100mL of 0.02mmol / L sodium ferrocyanide aqueous solution, adjust pH=3 with hydrochloric acid, let stand for 12 hours, wash with deionized water, and vacuum dry at 120℃ for 12 hours to obtain black Prussian blue complex powder, the Prussian blue complex is also known as FeNiPBA / NCT.

[0043] By replacing the ferric nitrate of this embodiment with ferric acetate and the nickel nitrate of this embodiment with nickel acetate, and otherwise following the same procedure as in this embodiment, the corresponding Prussian blue complex was prepared.

[0044] Comparative Example 1

[0045] The morphology of the FeNi@NCT powder prepared in step (1) of Example 1 is as follows: Figure 2 As shown in a.

[0046] Comparative Example 2

[0047] 2 mmol of anhydrous ferrous chloride was dissolved in 40 mL of water to obtain solution A. Solution A was then added to 100 mL of 0.02 mol / L sodium ferrocyanide aqueous solution, mixed thoroughly, and allowed to stand for 24 hours. The solution was then washed with deionized water and vacuum dried at 120 °C for 12 hours to obtain blue FePBA powder. (See attached image) Figure 2 As shown in b, the particles are cubic.

[0048] Comparative Example 3

[0049] 1.33 mmol of anhydrous ferrous chloride and 0.67 mmol of anhydrous nickel chloride were dissolved in 40 mL of water to obtain solution B. Solution B was poured into 100 mL of 0.02 mol / L sodium ferrocyanide aqueous solution, mixed thoroughly, and allowed to stand for 24 hours. The mixture was then washed with deionized water and vacuum dried at 120 °C for 12 hours to obtain blue FeNiPBA powder. (See attached image) Figure 2 As shown in c, these are smaller cubic particles.

[0050] Depend on Figure 3 It can be seen that after in-situ co-precipitation, the FeNi@NCT metallic phase disappeared and a FeNiPBA / NCT cubic phase was formed, indicating that the composite was successfully synthesized; moreover, the full width at half maximum (FWHM) was significantly narrowed, indicating a significant improvement in crystallinity and a reduction in defects. Figure 4 It can be seen that, compared with Comparative Examples 2 and 3, the interstitial water content of Example 1 is significantly reduced.

[0051] Example 4

[0052] The FePBA and FeNiPBA prepared in Comparative Examples 2 and 3, and the FeNiPBA / NCT prepared in Example 1 were used as cathode materials in sodium-ion batteries.

[0053] The method is as follows: The above materials are mixed with Ketjen black and polyvinylidene fluoride in a mass ratio of 7:2:1, and N-methylpyrrolidone is used as a solvent to prepare a uniform slurry. The slurry is uniformly coated on aluminum foil and vacuum dried at 70°C for 12 hours. The resulting material is then cut into 12mm diameter circles to serve as the positive electrode (loading mass: 1-2 mg / cm³). 2 The negative electrode was a 15.6 mm diameter sodium sheet, and the separator was a 16 mm glass fiber membrane. A CR2032 coin-shaped battery was assembled using 1 mol / L NaClO4 / EC:DEC (1:1) + 5% FEC as the electrolyte in a glove box under an argon atmosphere with H2O and O2 contents below 0.01 ppm. Electrochemical performance was then tested. Rate performance testing and constant-current intermittent titration analysis were performed using a LAND-CT3002A battery tester with a voltage window of 2-4.2 V and rate test current densities ranging from 0.05 A / g to 2.0 A / g. Electrochemical impedance spectroscopy (EIS) was measured on an Autolab potentiostat (PGSTAT302N) with a frequency range of 100 kHz-10 MHz.

[0054] Figure 5 This is a comparison chart of the battery rate performance obtained in Example 4. It can be seen that the rate performance of the composite material is significantly improved. Figure 6 The smaller diameter semicircle in the high-frequency region and the larger slope straight line in the low-frequency region, as shown in the electrochemical impedance spectroscopy comparison diagram, can respectively prove that the impedance is smaller and the ion diffusion is faster. Figure 7 The diffusion coefficient comparison graph fitted by the constant current intermittent titration test shows that the sodium ion diffusion coefficient of FeNiPBA / NCT (Example 1) is an order of magnitude higher than that of the other comparative samples. The above analyses all indicate that the stronger rate performance of the composite obtained in Example 1 is mainly due to the rapid electron / ion diffusion promoted by the construction of the conductive network.

[0055] Example 5

[0056] The FeNi@NCT, FePBA, and FeNiPBA prepared in Comparative Examples 1, 2, and 3, and the FeNiPBA / NCT prepared in Example 1, were used as cathode materials in sodium-ion batteries. (See below) Figure 8 It can be seen that FeNiPBA / NCT retains 83.5% of its initial capacity after 2000 cycles at 1.0 A / g, which is significantly better than other comparative examples. The inhibition of its degradation mainly comes from Fe. 2+ and Ni 2+ The synthesis process slowly releases the enhanced intrinsic crystallinity and the reduced cyclic strain accumulation due to Ni doping.

[0057] Experiments have shown that the CR2032 coin-shaped battery prepared by the Prussian blue composite prepared in Example 2 or 3 according to the method of Example 4 has similar rate performance and cycle stability to the CR2032 coin-shaped battery prepared by the Prussian blue composite prepared in Example 1 according to the method of Example 4.

Claims

1. A method for the preparation of a Prussian blue complex, characterized in that Includes the following steps: (1) The carbon source / nitrogen source, iron salt and nickel salt are uniformly dispersed in ethanol, dried and calcined under an inert atmosphere to obtain FeNi@NCT; (2) Disperse the FeNi@NCT in an aqueous solution of sodium ferrocyanide, adjust the pH to 0.5-3 with hydrochloric acid, let it stand, wash with deionized water, and dry to obtain the Prussian blue complex, also known as FeNiPBA / NCT; the carbon source / nitrogen source is melamine, urea or dicyandiamide.

2. The production method according to claim 1, characterized by The cation molar ratio of the iron salt and nickel salt in step (1) is 1-3:1, and the mass of the carbon source / nitrogen source is 2-4 times the total mass of the iron salt and nickel salt.

3. The production method according to claim 1 or 2, characterized by The anions of the iron salt include chloride, sulfate, nitrate or acetate.

4. The production method according to claim 1 or 2, characterized by The anions of the nickel salt include chloride, sulfate, nitrate, or acetate.

5. The method of claim 1, wherein The inert atmosphere is argon or nitrogen, the calcination temperature is 700-900℃, and the calcination time is 1 hour.

6. The method of claim 1, wherein The ratio of FeNi@NCT to a 0.02 mol / L sodium ferrocyanide aqueous solution is 1 g: 10-100 mL.

7. The method of claim 1, wherein The pH is 1, and the standing time is 12-36 hours.

8. A Prussian blue complex prepared by any one of the preparation methods of claims 1 to 7.

9. The use of the Prussian blue composite of claim 8 in the preparation of a sodium-ion battery cathode.

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